What are these bladder snail parasites?

I collected some bladder snails several months ago. While checking them out one day, I noticed that they were now infested with worm-like ectoparasites.

Appearance and behavior

Here's a picture of a snail with a bunch of the worms hanging off of it's head, where they tend to congregate. I've also circled one of the worms crawling along the glass.

I sampled some of the worms and took a look at them under a microscope. Here's a video ("Video 1" below) I recorded of one of them crawling around. They have some notable characteristics.

First, they appear to have some sort of sucker mouth.

Second, they have some interesting "legs" tipped with hairs (?) at the ends of their tails. Here's a short video ("Video 2" below) of a worm writhing around that shows them off a little better than pictures do. They appear to be in pairs of two.

Animated clips from the linked videos:

Video 1 (left) and Video 2 (right)

The length of the worms ranges from 1-5 mm (edit: they get larger; see below).

Update: After keeping infected snails for a while longer, I believe that these worms only parasitize bladder snails when the worms are young (within the aforementioned size range). Larger, adult worms appear to be free-living and growing up to 1-1.5cm, and will actually crawl away when snails disturb them. Here is a picture of an adult specimen (along with some smaller ones), no microscope required:

Here's a much better picture of the hair-like legs, of which this adult specimen has numerous pairs:

Lastly, here's a very interesting detail: These worms are highly specialized, and do not seem to affect ramshorn or pond snails, which I have numerous of in the same tank, in the slightest. It's only the bladder snails that end up infested.


These snails were gathered in Canada, in a still-water area connected to the Oldman River. The river is accessible by cows and deer.


I have witnessed the snails shedding tons of cercariae into the water, which eventually disappear after a couple of hours (reinfect the snails?). I'm not sure if those are related to this worm, or if the snails are also infected with some other type of fluke.

Update: I now believe the aforementioned cercariae are unrelated to the worm in question. I managed to record an adult worm releasing numerous live young, which resemble tadpoles (trochophores?):

I've recorded a video of the worm giving birth that can be viewed here (left image below). The young seem to be stored in chambers inside of the parent, and then are pumped through the body and out the back end. While the young appear to be still in the video, some of them are quite active (right image below).

My theory at this point is that the young penetrate snails, grow inside of them, emerge and hang onto the host for a while, and then eventually dismount as free-living adults. Adult worms seem to be independent, while smaller worms hang off of the host the snail (feeding off of it?) until they're large enough to live freely.


I would like to eliminate these worms if possible (I can't gather more snails any time soon, and they eventually kill off smaller snails). My first attempt was dosing with praziquantel, which is supposedly effective against flukes while being snail-friendly. Unfortunately, three days later, one of the snails died, and the worms appear to be unharmed.

Update: I gathered some more snails, and attempted praziquantel once again. While it did not harm the snails, it also continued to be ineffective against the worms. I have been experimenting with Seachem ParaGuard, and the results seem to be positive for minor infestations, but not against fully mature worms.


After some research, my best guess is that they're trematodes from the class Digenea-- They appear have sucker mouths, can parasitize snails exclusively, can have a free-swimming form, and can shed cercariae. That said, I'm not terribly confident, and would ideally like to be able to identify them more specifically.

I have finally figured out what these are, and it turns out I greatly misunderstood their relationship with snails.

These worms are annelids of the genus Chaetogaster, specifically Chaetogaster limnaei limnaei.

Source: Page 653 of "Fresh-water biology" (1918)

Ch. l. limnaei is unique in its genus in that lives on the bodies and in the shells of snails, including Physa spp. like the Physa acuta snails in question. While the relationship was originally thought to be parasitic by early researchers, it turns out that it's actually commensalistic (or even mutualistic in some scenarios).

From this vantage point the worms feed on various microorganisms, such as rotifers and algae, and small particles stirred up by the host snail scavenging for food. They also feed upon the cercariae and metacercariae of fluke species that parasitize the snails, even able to protect the snails from getting infected in the first place.

That said, it's not all good-- Snails with heavy infestations of Ch. l. limnaei have been shown to be less active, spending more time in their shells rather than out and foraging for food (Stoll et al., 2013). Additionally, worms have been experimentally shown to consume tissues of their hosts when food is low or nonexistent (Stoll et al., 2013).

To respond to a few points from the question:

These worms are highly specialized, and do not seem to affect ramshorn or pond snails, which I have numerous of in the same tank, in the slightest. It's only the bladder snails that end up infested.

Ch. l. limnaei is not restricted to bladder snails, and will happily live on pond snail and ramshorn species. It's possible that the bladder snails had more severe fluke infestations which the worms found preferable.

My theory at this point is that the young penetrate snails, grow inside of them, emerge and hang onto the host for a while, and then eventually dismount as free-living adults. Adult worms seem to be independent, while smaller worms hang off of the host the snail (feeding off of it?) until they're large enough to live freely.

This worm is able to reproduce both asexually through budding, but also sexually as shown here. Sexual reproduction often occurs in the winter, where the worm lives freely and reproduces sexually before returning to snail hosts in the spring.

I would like to eliminate these worms if possible

I found a blog post by someone struggling with the same problem:

One day (do not know it exactly, probably few months later) I noticed that all worms disappeared. I did not know why they were gone.

Later I found the reason in the 1974 thesis. Chaetogaster limnaei limnaei is highly sensitive to temperatures above 24 °C. Such a temperature reduces or completely eliminates these worms. Therefore, If you transport worms from their natural environment to your tropical aquarium, there is no need to worry. If you have aquaria with aquarium heater, they are bound to be killed by high temperature. Worms are killed in summer heat as well.

This seems to be accurate, as with the onset of the summer heat, I no longer have any of these worms present on my snails. Now knowing what they were, it almost feels like a shame-- They were protectors, not foes.



The parasites that cause schistosomiasis live in certain types of freshwater snails. The infectious form of the parasite, known as cercariae, emerge from the snail, hence contaminating water. You can become infected when your skin comes in contact with contaminated freshwater. Most human infections are caused by Schistosoma mansoni, S. haematobium, or S. japonicum.

What is schistosomiasis?

Schistosomiasis, also known as bilharzia, is a disease caused by parasitic worms. Infection with Schistosoma mansoni, S. haematobium, and S. japonicum causes illness in humans less commonly, S. mekongi and S. intercalatum can cause disease. Although the worms that cause schistosomiasis are not found in the United States, more than 200 million people are infected worldwide.

What is schistosomiasis?

Schistosomiasis, also known as bilharzia, is a disease caused by parasitic worms. Infection with Schistosoma mansoni, S. haematobium, and S. japonicum causes illness in humans less commonly, S. mekongi and S. intercalatum can cause disease. Although the worms that cause schistosomiasis are not found in the United States, more than 200 million people are infected worldwide.

How can I get schistosomiasis?

Infection occurs when your skin comes in contact with contaminated freshwater in which certain types of snails that carry schistosomes are living.

Freshwater becomes contaminated by Schistosoma eggs when infected people urinate or defecate in the water. The eggs hatch, and if certain types of freshwater snails are present in the water, the parasites develop and multiply inside the snails. The parasite leaves the snail and enters the water where it can survive for about 48 hours. Schistosoma parasites can penetrate the skin of persons who are wading, swimming, bathing, or washing in contaminated water. Within several weeks, parasite mature into adult worms, residing in the blood vessels of the body where the females produce eggs. Some of the eggs travel to the bladder or intestine and are passed into the urine or stool.

What are the signs and symptoms of schistosomiasis?

Within days after becoming infected, you may develop a rash or itchy skin. Fever, chills, cough, and muscle aches can begin within 1-2 months of infection. Most people have no symptoms at this early phase of infection.

Eggs travel to the intestine, liver or bladder, causing inflammation or scarring. Children who are repeatedly infected can develop anemia, malnutrition, and learning difficulties. After years of infection, the parasite can also damage the liver, intestine, lungs, and bladder. Rarely, eggs are found in the brain or spinal cord and can cause seizures, paralysis, or spinal cord inflammation.

Symptoms of schistosomiasis are caused by the body's reaction to the eggs produced by worms, not by the worms themselves.

What should I do if I think I have schistosomiasis?

See your health care provider. If you have traveled to countries where schistosomiasis is found and had contact with freshwater, describe in detail where and for how long you traveled. Explain that you may have been exposed to contaminated water.

How is schistosomiasis diagnosed?

Your health care provider may ask you to provide stool or urine samples to see if you have the parasite. A blood sample can also be tested for evidence of infection. For accurate results, you must wait 6-8 weeks after your last exposure to contaminated water before the blood sample is taken.

What is the treatment for schistosomiasis?

Safe and effective drugs are available for the treatment of schistosomiasis. You will be given pills to take for 1-2 days.

Am I at risk?

If you live in or travel to areas where schistosomiasis occurs and your skin comes in contact with freshwater from canals, rivers, streams, ponds, or lakes, you are at risk of getting schistosomiasis.

In what areas of the world does schistosomiasis occur?

How can I prevent schistosomiasis?


Schistosomiasis is an important cause of disease in many parts of the world, most commonly in places with poor sanitation. School-age children who live in these areas are often most at risk because they tend to spend time swimming or bathing in water containing infectious cercariae.
If you live in, or travel to, areas where schistosomiasis is found and are exposed to contaminated freshwater, you are at risk. Areas where human schistosomiasis is found include:


Causal Agent:

Schistosomiasis is caused by digenetic blood trematodes. The three main species infecting humans are Schistosoma haematobium, S. japonicum, and S. mansoni. Two other species, more localized geographically, are S. mekongi and S. intercalatum. In addition, other species of schistosomes, which parasitize birds and mammals, can cause cercarial dermatitis in humans.

Life Cycle:

Eggs are eliminated with feces or urine. Under optimal conditions the eggs hatch and release miracidia , which swim and penetrate specific snail intermediate hosts. The stages in the snail include 2 generations of sporocysts and the production of cercariae. Upon release from the snail, the infective cercariae swim, penetrate the skin of the human host, and shed their forked tail, becoming schistosomulae. The schistosomulae migrate through several tissues and stages to their residence in the veins. Adult worms in humans reside in the mesenteric venules in various locations, which at times seem to be specific for each species. For instance, S. japonicum is more frequently found in the superior mesenteric veins draining the small intestine, and S. mansoni occurs more often in the superior mesenteric veins draining the large intestine. However, both species can occupy either location, and they are capable of moving between sites, so it is not possible to state unequivocally that one species only occurs in one location. S. haematobium most often occurs in the venous plexus of bladder, but it can also be found in the rectal venules. The females (size 7 to 20 mm males slightly smaller) deposit eggs in the small venules of the portal and perivesical systems. The eggs are moved progressively toward the lumen of the intestine (S. mansoni and S. japonicum) and of the bladder and ureters (S. haematobium), and are eliminated with feces or urine, respectively. Pathology of S. mansoni and S. japonicum schistosomiasis includes: Katayama fever, hepatic perisinusoidal egg granulomas, Symmers´ pipe stem periportal fibrosis, portal hypertension, and occasional embolic egg granulomas in brain or spinal cord. Pathology of S. haematobium schistosomiasis includes: hematuria, scarring, calcification, squamous cell carcinoma, and occasional embolic egg granulomas in brain or spinal cord.

Human contact with water is thus necessary for infection by schistosomes. Various animals, such as dogs, cats, rodents, pigs, hourse and goats, serve as reservoirs for S. japonicum, and dogs for S. mekongi.

Life cycle image and information courtesy of DPDx.


Infection occurs when skin comes in contact with contaminated freshwater in which certain types of snails that carry the parasite are living. Freshwater becomes contaminated by Schistosoma eggs when infected people urinate or defecate in the water. The eggs hatch, and if the appropriate species of snails are present in the water, the parasites infect, develop and multiply inside the snails. The parasite leaves the snail and enters the water where it can survive for about 48 hours. Schistosoma parasites can penetrate the skin of persons who come in contact with contaminated freshwater, typically when wading, swimming, bathing, or washing. Over several weeks, the parasites migrate through host tissue and develop into adult worms inside the blood vessels of the body. Once mature, the worms mate and females produce eggs. Some of these eggs travel to the bladder or intestine and are passed into the urine or stool.

Symptoms of schistosomiasis are caused not by the worms themselves but by the body&primes reaction to the eggs. Eggs shed by the adult worms that do not pass out of the body can become lodged in the intestine or bladder, causing inflammation or scarring. Children who are repeatedly infected can develop anemia, malnutrition, and learning difficulties. After years of infection, the parasite can also damage the liver, intestine, spleen, lungs, and bladder.

Common Symptoms

Most people have no symptoms when they are first infected. However, within days after becoming infected, they may develop a rash or itchy skin. Within 1-2 months of infection, symptoms may develop including fever, chills, cough, and muscle aches.

Chronic schistosomiasis

Without treatment, schistosomiasis can persist for years. Symptoms of chronic schistosomiasis include: abdominal pain, enlarged liver, blood in the stool or blood in the urine, problems passing urine, and increased risk of bladder cancer.

Rarely, eggs are found in the brain or spinal cord and can cause seizures, paralysis, or spinal cord inflammation.


Stool samples can be examined microscopically for parasite eggs (S. mansoni or S. japonicum) or urine (S. haematobium). The eggs tend to be passed intermittently and in small amounts and may not be detected, so it may be necessary to perform a blood (serologic) test.


Those who have had contact with potentially contaminated water overseas should see their health care provider after returning from travel to discuss testing.

Stem Cells Discovered in Deadly Parasitic Flatworms

The flatworms that cause the tropical disease schistosomiasis can live and reproduce inside infected humans for decades. In a new study, researchers identified the stem cells that may be responsible. The discovery could lay the groundwork for new strategies to treat the devastating disease caused by the parasite.

Schistosomiasis, also known as bilharzia or snail fever, primarily affects people living in the tropical regions of developing countries. Children who are repeatedly infected can develop anemia, malnutrition and learning difficulties. After years of infection, the parasite can damage the liver, intestine, lungs and bladder. Rarely, it can also cause seizures, paralysis or spinal cord inflammation. More than 200 million people have this disease and more than 700 million people are at risk of infection.

Microscopic Schistosoma parasites infect people who are wading, swimming or bathing in freshwater inhabited by infected snails. The parasites, known as schistosomes, burrow into human skin and then grow inside blood vessels. Female worms produce eggs that can travel to the intestine, liver, bladder or other organs. The eggs can be released back into the water through urine or feces, starting the cycle again.

Dr. Phillip Newmark and colleagues at the University of Illinois have spent years studying flatworms. They knew that planarians, non-parasitic worms popular in biology classrooms, have a type of stem cell known as a neoblast. Neoblasts allow planarians to regenerate damaged organs and body parts. The scientists wondered whether schistosomes might have a similar type of stem cell. Their study, described in Nature on February 28, 2013, was funded in part by NIH’s Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) and National Institute of Allergy and Infectious Diseases (NIAID).

The scientists used a labeling technique to identify a population of cells from schistosomes that was able to grow and divide. They found that these cells had a distinct structure and pattern of gene expression similar to neoblasts. When the researchers used a fluorescent marker to tag the cells, they detected the marker in new cells 3 days later. This ability to divide and produce new cells is a key characteristic of stem cells.

The scientists injected schistosome-infected mice with a marker to look at the pattern of tagged cells at several time points. They located the tag in intestinal cells and in body wall muscle cells of the parasite after 7 days. This revealed that the cells could turn into different types of cells (differentiate), another key behavior of stem cells.

The team next turned their attention to signal pathways that might exist within these stem cells. Using their knowledge of planarians, they focused on the fibroblast growth factor (FGF) receptor family, which is expressed in proliferating planarian cells. They identified a gene, SmfgfrA, in the adult stem cells that codes for the parasite’s version of a FGF receptor. Using a technique called RNA interference (RNAi), they turned off the gene and found that it’s required for maintenance of the stem cells in the worm.

“We started with the big question: How does a parasite survive in a host for decades?” says Newmark. “That implies that it has ways of repairing and maintaining its tissues. This study gives us insight into the really interesting biology of these parasites, and it may also open up new doors for making their life cycle a lot shorter.”

How Is NIAID Addressing This Critical Topic?

NIAID-supported investigators study many aspects of schistosomiasis to find new ways to prevent and treat the disease. Research is directed at the various life-stages of parasite itself as well as the freshwater snails that serve as an intermediate host.

Like other so-called neglected tropical diseases (NTDs), schistosomiasis generally impacts the world’s poorest people. Learn about NIAID research efforts on other NTDs.

The NIAID-funded Schistosomiasis Research Center provides investigators with a number of resources to advance their studies, including egg and larval parasites, snails and molecular reagents and other tools needed to conduct research.

This video describes the resources available from the Schistosomiasis Research Center.

To learn about risk factors for schistosomiasis and current prevention and treatment strategies visit the Centers for Diseases Control and Prevention (CDC) schistosomiasis site.

MEDICAL microbiology

  • A living organism which receives nourishment and shelter from another organism where it lives is called parasites.
  • A parasite does not necessarily cause disease.
  • Simply parasitism is living in association with the host.
  • The parasite derives all benefits from the association and the host may either not be harmed or may suffer the consequences of this association, a parasite disease.
  • A parasite is an organism that is entirely dependent on another organism, referred to as its host, for all or part of its life cycle and metabolic requirements.

  • All are flagellates.
  • They have one or more whip like flagella for locomotion at some stage of their life cycle. In some cases, there is the presence of undulating membrane (Eg. Trypanosoma).
  • The mastigophore includes the intestinal and genitourinary flagellates and the blood and tissue flagellates.
  • The intestinal and genitourinary flagellates are Giardia, Trichomonas, Dientamoeba, Chilomastik, etc.
  • The blood and tissue flagellates are Trypanosoma, Leishmania, etc.
  • They reproduce asexually by binary fission.
  • They are all typically amoeboid and include Entamoeba, Endolimax, Iodamoeba, Naegleria, Acanthamoeba, etc. amoebae consist of a shapeless mass of moving cytoplasm which is divided in to granular endoplasm and clear ectoplasm.
  • They move by pushing out the ectoplasm to form pseudopodia (false feet) into which the endoplasm then low.
  • Amoebae reproduce asexually by simply dividing into two (binary fission)
  • These are tape-like, segmented and hermaphrodite organism. They have suckers in their head and in some species also hooks that attach he tapewor to its host.. It consists of a head (scolex) and many proglottids.
  • Alimentary canal and body cavity are absent. Examples are Diphyllobothrium, Taenia, Echinococcus, Hymenolepsis, etc.
  • They are leaf-like unsegmented organism. Sexes are not separate except Schistosomes which are diecious. They don’t have hooks and suckers in their head. Alimentary canal is present but is not complete (anus absent).
  • The body cavity is absent.
  • Examples are Schistosoma, Gastrodiscoides, Fasciolopsis, Fasciola, Clonorchis, Heterophyes, etc.
  • Their body is elongated, cylindrical and unsegmented. Sexes are separate (diecious). They also lack hooks and suckers.
  • They possess the complete alimentary canal and body cavity. Examples are:
  • History of discovery of the parasite
  • Geographical distribution
  • Habitat inside the human host
  • Morphology and life cycle
  • Modes of infection: Reservoir host, source of infection, portal of entry, vehicle of transmission
  • Effects of the parasites: pathogenic lesions, clinical manifestations
  • Immunological responses
  • Methods for specific diagnosis
  • Approved therapy for eradication of parasitic infection
  • Prophylactic measures for the prevention of parasitic infection of the individual as well as of the community.
  1. Ectoplasm: the external hyaline portion its function is protective, locomotive and sensory.
  2. Endoplasm: the internal granular portion its function is nutritive and reproductive
  1. Pseudopodia: prolongation of temporary ectoplasmic process, seen in Rhizopodea (E. histolytica)
  2. Flagella: long delicate thread-like filaments, seen in Zoomastigophorea. (Giardia intestinalis)
  3. Cilia: fine needle-like filaments covering the entire surface of the body, seen in Ciliatea. (B. coli)
  4. Contractile vacuoles: situated inside the endoplasm excretory function.
  5. Rudimentary digestive organ, such as cytostome (cell mouth) and cytopharynx, seen in Balantidium coli.
  6. Cyst wall: a thickened resistant wall, seen in the cystic stage

  • A protozoal parasite may multiply vigorously by asexual method for a long time, and later by a change of process it either has recourse to sexual method of reproduction or undergoes encystment for a change of its host.
  • The sexual method of reproduction often occurs in a different host other than the one utilized for asexual multiplication the process is known as alternation of generation accompanied by alternation of host, as seen in Plasmodia.
  • A protozoal parasite may pass its life cycle in one or two hosts.

  1. These are leaf-shaped, unsegmented flat worms, called flukes.
  2. Size varies from 1 mm to several cm in length.
  3. The organs of attachment are two strong muscular cup-shaped depressions, called suckers. The one surrounding the mouth is called the oral sucker and the other, on the ventral surface of the body, is called the ventral sucker (acetabulum).
  4. Sexes are not separate, i.e., each individual worm is hermaphrodite (monoecious) except the Schistosomes.
  5. Body cavity is absent.
  6. The alimentary canal is present but incomplete. The anus is absent. The oesophagus bifurgates in front of the ventral sucker in to a pair of blind intestinal caeca or crura which may be simple (as in C. sinensis) or branched (as in F. hepatica) or may reunite to form a single caecum (as in Schistosomes).
  7. Excretory and Nervous systems are present.
  8. Excretory system consists of “flame cells” and collecting tubules which opens posteriorly, in to excretory pore.
  9. Reproductive system is highly developed and complete in each individual. The genital organ lie between the two branches of the intestine.
  10. The worm is oviparous, since eggs are liberated.
  11. Eggs are all operculated (with lid) (except those of Schistosomes) and can developed only in water. Trematode eggs do not float in saturated solution of common salt
  1. The Nematodes are unsegmented worms with out any appendage. They are elongated and cylindrical in appearance both ends often pointed.
  2. The size show a great variation (5 mm- up to 1 m) D. medinensis measuring 1 meter or more.
  3. The body is covered with a tough cuticle.
  4. The worm possesses a body cavity in which the various organs, such as digestive and genital systems float.
  5. Excretory and nervous system are rudimentary.
  6. The alimentary canal is complete, consisting of an oral aperature, mouth cavity, oesophagus, intestine and a subterminal anus.
  7. The nematodes of man are all diecious helminths. The male is generally smaller than the female and its posterior end is curved or coiled Ventrally.
  8. Females are either viviparous (produce larvae) or oviparous (lay eggs)
  9. The discharged eggs may hatch directly into infective larvae or they may require special conditions in which to hatch and up to three developmental stages before becoming infective larvae. Each stage involves a shedding of the old cuticle (moulting).
  • by contamination of food or drink
  • by contamination of the skin or mucous membrane
  • by the agency of insect host
  • by contamination of food or drink- gain entrance in to the digestive tract. Example Cysts of E. histolytica, eggs of A. lumbricoides after contaminating with food or drink the infective forms may remains in the flesh of some intermediate hosts
  • beef containing the larval stages of T. saginata
  • pork containing the larval forms of T. solium
  • crab or crayfish containing metacercerial forms of P. westermani
  • sometimes the intermediate host harbouring the infective form may be taken up as a whole eg: Cyclops infected with a larval forms of Dracunculus medinensi are ingested with water
  • the infective forms may come out its intermediate host and encyst in aquatic plants, eaten as food by man. Eg: metacercarial forms of F. hepatica
  • by contamination of the skin or mucous membrane
  1. the filariform larvae of A. duodenale, N. americanus which abound in damp soil, may penetrate the unbroken skin of an individual walking over such places bare-footed.
  2. The cercarial forms of S. haematobium and S. mansoni and S. japonicum in infected water, may penetrate the skin of a person coming in contact with such water.
  3. by the agency of insect host
  4. an infected blood sucking arthropod may introduce the organism directly in to the blood or in to the skin or in to the skin layers at the time of obtaining a blood-meal.
  5. Eg: Leishmania by Phlebotomous (sandfly)
  6. Wuchereria by Culicin mosquitoes
  7. Plasmodia by Anopheline mosquitoes
  8. In this group, the parasites undergo a biological development for a certain period before becoming infective to man.
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Cloves are another effective remedy for parasites, as they help to destroy the eggs before they have a chance to hatch.

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As a sign of gratitude for how my husband was saved from Schistosomiasis , i decided to reach out to those still suffering from this.My husband suffered Schistosomiasis and it was really tough and heartbreaking for me because he was my all and the symptoms were terrible, we tried various therapies prescribed by our neurologist but none could cure him. I searched for a cure and i saw a testimony of so many people who was cured from Schistosomiasis . and so many other with similar body problem, and they left the contact of the doctor who had the herbal cure to Schistosomiasis . I never imagined Schistosomiasis has a cure not until i contacted him and he assured me my husband will be fine. I got the herbal medication he recommended and my husband used it and in one months he was fully okay even up till this moment he is so full of life. Schistosomiasis has a cure and it is a herbal cure contact the doctor for more info on [email protected] on how to get the medication. Thanks for reading my testimony .

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What is bilharzia, snail fever, or schistosomiasis?

Bilharzia, or “snail fever,” is a disease caused by a parasitic worm. The worm, or fluke, has several different species. It affects the intestines and the urinary system preferentially, but because it lives in the blood vessels, it can harm other systems in the body too.

The World Health Organization (WHO) describe bilharzia — now mostly known as schistosomiasis — as both an acute and chronic disease. Symptoms appear as the body reacts to the parasite’s presence, but complications can persist long-term.

The disease can affect different parts of the body, including the lungs, the nervous system, and the brain. The area of damage will depend on the species of parasite.

Bilharzia is not usually fatal immediately, but it is a chronic illness that can seriously damage the internal organs. In children, it can lead to reduced growth and problems with cognitive development.

Some types of bilharzia can affect birds and mammals, such as water buffalo.

Share on Pinterest Schistosomiasis or bilharzia is passed on by a parasite that is present in fresh water in some places.

According to the WHO , the infection starts when a person comes into direct contact with fresh water where certain types of water snail carry the worm.

The parasites enter the body when a person is swimming, washing, or paddling in contaminated water. They can also become infected by drinking the water or eating food that a person has washed in untreated water.

The infective form of the fluke is known as cercariae. The cercariae emerge from the snails, pass through a person’s skin when they are in the water, and develop into adult worms that live in the individual’s blood.

Depending on the type of worm, bilharzia can affect:

  • the intestines
  • the urinary system, increasing the risk of bladder cancer
  • the liver
  • the spleen
  • the lungs
  • the spinal cord
  • the brain

The infection cycle of the parasite begins when the worm’s eggs enter fresh water through the feces and urine of humans who already have the infection.

The eggs hatch in the water, releasing tiny larvae, and the larvae reproduce inside the water snails.

After they have infected water snails, the worm’s cercariae, are released. The cercariae can survive for up to 48 hours.

The cercariae can penetrate human skin and enter the bloodstream. There, they travel through the blood vessels of the lungs and liver, and then to the veins around the bowel and bladder.

After some weeks, the worms are mature. They mate and start producing eggs. These eggs pass through the walls of the bladder, the intestine, or both. Eventually, they leave the body through urine or feces. At this point, the cycle starts again.

A person with schistosomiasis cannot pass it on to another person. Humans only become infected through contaminated water where the snails are living.

More than 200 million people have bilharzia worldwide, according to the Centers for Disease Control and Prevention (CDC), although the parasite is not present in the United States.

Places where the parasite occurs include :

  • Africa, including Egypt and the Nile Valley
  • South America and parts of the Caribbean
  • Southeast Asia
  • Yemen, in the Middle East

Bilharzia can affect people of any age in an affected area, but those who are most at risk include:

  • children
  • people who swim, work, or have other contacts with freshwater rivers, canals, lakes, and streams

Bilharzia does not occur in the U.S., but people have developed the rash known as swimmer’s itch, or cercarial dermatitis, after exposure to a related species of schistosomes, the parasite that causes bilharzia.

Health authorities have investigated outbreaks of cercarial dermatitis in Stubblefield Lake in northern New Mexico, and one in Prospect Lake in the heart of Colorado Springs, Colorado.

Americans are at risk of infection if they travel to areas where the disease exists. Anyone who is visiting these regions should check with a doctor about any precautions they may need to take.

A world of parasites

When we humans look at a landscape, whether African savanna or Australian coral reef, we see the other host species, like ourselves. But the lions and zebras and fish are just homes for most of the life hidden in front of us.

All told, 40 percent of known animals are parasites, and those are just the ones that have been described. Scientists think that’s only about 10 percent of all the parasites out there, leaving potentially millions more yet to be discovered. Parasitic wasps alone probably outnumber any other group of animals, even beetles.

Most species, it turns out, are parasitized by multiple others. Take humans: Despite our efforts to be unhospitable, we’re excellent hosts. More than a hundred different parasites have evolved to live in or on us, many of them now dependent on us for their species’ continued existence.

Parasites proliferate because every living thing is a smorgasbord of nutrients and energy, and being a top predator isn’t the only way to get a bite of that bounty. Parasites opt out of the arms race between predator and prey entirely, choosing an easier path. It’s clever, when you think about it, and it’s exactly why parasitism is so common. “Nature abhors a vacuum. If there’s an opportunity, someone’s going to evolve to fill it,” says Wood.

Parasitism has evolved as a way of life again and again, over billions of years, from the smallest and simplest microbes to the most complex vertebrates. There are parasitic plants, parasitic birds, a bewildering array of parasitic worms and insects, and even a parasitic mammal—the vampire bat, which survives by drinking the blood of cows and other mammals. Of the 42 major branches on the tree of life, called phyla, 31 are mostly parasites.

Yet we have barely begun to identify all the parasites, much less learn their lifestyles or monitor their populations. “That’s just not something that we’ve ever really prioritized,” says Skylar Hopkins, an ecologist at North Carolina State University. So a few years ago, Hopkins pulled together a group of scientists interested in parasite conservation, and they started sharing what they knew. In 2018 they presented research at the Ecological Society of America conference. Then, in October 2020, they published the first-ever global plan for saving parasites in a special issue of the journal Biological Conservation.

There should be, potentially, millions of parasite species that are threatened, and probably a lot that have already gone extinct.

One of the things Hopkins and her colleagues have noticed is what they call the paradox of co-extinction. Since parasites by definition need other species, they’re particularly vulnerable to the phenomenon. Take, for example, the endangered pygmy hog-sucking louse. It lives only on another critically endangered species, the pygmy hog, which is disappearing from the grasslands it inhabits in the foothills of the Himalaya.

“There should be, potentially, millions of parasite species that are threatened, and probably a lot that have already gone extinct,” Hopkins says. “But the weird thing is that we’ve hardly documented any parasite extinctions.”

Wood says she has been hunting for historical data on parasite abundance for more than a decade, for any parasite—on land or in the water. “I’ve had my eyes peeled,” she says, and so far, she has found a grand total of two useful data sets: one from a research cruise in the late 1940s and the other in a lab notebook kept by one of her mentors.

With so little information, “we have no idea whether parasites are playing the same role now that they did in the past,” Wood says. “I think that’s a travesty.”

The poster child for parasite conservation, if there is one, is the California condor louse, an ironic victim of the conservation movement itself. In the 1970s, desperate to save the California condor, biologists began rearing the birds in captivity. Part of the protocol was to de-louse every bird with pesticides, on the assumption that parasites were bad for condors, though it’s not clear they actually were. The California condor louse hasn’t been seen since.

Similarly, the New England medicinal leech hasn’t been seen for over a decade, and overfishing has probably done in the marine fluke Stichocotyle nephropis, which depended on endangered rays and skates to complete its life cycle. Untold other parasitic worms, protozoans, and insects are presumed to have gone down with the ship, so to speak, as their hosts died out.

Mass spectrometry

Mass spectrometry is an analytical method used to determine the elemental composition of a sample or molecule. It can be used for both qualitative and quantitative measurements. Not only is it an important method for protein analysis, it is also widely used in space missions to characterise the composition of heavenly bodies. The principle consists of ionising the molecules or molecule fragments in the sample and then measuring their mass-to-charge ratios.

The machine used for this method, a mass spectrometer, is generally composed of three sections (see image below):

  • The mass analyser, where electromagnetic fields are applied to separate the ions by their mass-to-charge ratio. These fields exert forces on the ions the electric field may speed up or slow down a charged particle, and its direction may be altered by the magnetic field. The magnitude of the deflection of the moving ion’s trajectory depends on its mass-to-charge ratio: according to Newton’s second law of motion, lighter ions are deflected by the magnetic force more than heavier ions.

A schematic representation of a mass spectrometer

This information is then used to determine the chemical element composition of the original sample.

What are these bladder snail parasites? - Biology

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What is schistosomiasis?

Schistosomiasis is a disease caused by a parasite worm that lives in certain types of freshwater snails. The parasite leaves the snail and enters the water where is can enter a person&rsquos body through the skin when a person wades or swims in contaminated freshwater.

Within days of becoming infected, a person may develop a rash or itchy skin. Fever, chills, cough, and muscle aches may begin within one to two months of infection. Most people have no symptoms early on, but left untreated, schistosomiasis can cause more serious health problems.

Children who are repeatedly infected can develop anemia, malnutrition, and learning difficulties. After years of infection, the parasite can also damage the liver, intestine, spleen, lungs, and bladder.

Who is at risk?

Travelers going to countries in Africa, South America, the Middle East, China, and Southeast Asia can get schistosomiasis. The freshwater snails that carry schistosomiasis are found in streams, rivers, and lakes in many countries around the world. Anyone who swims, bathes, or wades in freshwater streams, rivers, ponds, lakes, or untreated pools where snails that carry schistosomiasis live can get infected.

Many travelers who get schistosomiasis traveled to sub-Saharan Africa to popular tourist destinations. These include rivers and water sources such as Lake Malawi, Lake Tanganyika, Lake Victoria, the Omo River, the Zambezi River, and the Nile River.

Adventure travelers, Peace Corps volunteers, missionaries, soldiers, and ecotourists may be more likely to get schistosomiasis because of their work and activities. Local claims that there is no schistosomiasis in a body of freshwater are not reliable and precautions should be taken to prevent exposure.

What can travelers do to prevent schistosomiasis?

If you are visiting or live in an area where schistosomiasis is a concern:

  • Avoid swimming, bathing, or wading in freshwater sources, such as lakes, rivers, ponds, and wetlands. Swimming in the ocean and in chlorinated swimming pools is safe.
  • Drink safe water.
    • Although schistosomiasis is not transmitted by swallowing contaminated water, if contaminated water touches your mouth or lips, you could become infected.
    • Because water coming directly from canals, lakes, rivers, streams, or springs may be contaminated with other infectious organisms, bring your water to a rolling boil for one minute or filter water before drinking it. A rolling boil for at least one minute will kill any harmful parasites, bacteria, or viruses present.
    • Iodine treatment alone WILL NOT GUARANTEE that water is safe and free of all parasites.

    If you traveled and feel sick, particularly if you have a fever, talk to a healthcare provider and tell them about your travel. Avoid contact with other people while you are sick.

    Snails are invertebrate animals, belonging to the Phylum Mollusca. This group of organisms (except slug) possess a unique feature, known as “shell” which is a major characteristic of the group [1]. The snails inhabits a wide range of habitats because they are found not only in freshwater environment but also in other ecological niches [2].

    Some snails are medically important because they transmit disease-causing trematodes in humans and other animals [3]. Most of the diseases caused by snail-borne trematodes are prevalent in the tropic and sub-tropic regions of the world, and the medical and economic burden of these diseases are often neglected which is why they are called neglected tropical diseases (NTDs). The distribution of the diseases caused by snail-borne trematodes especially schistosomiasis is focal. Hence, the parasites distribution is strongly dependent on the intermediate snail hosts distribution [4, 5].

    Firstly, the continued transmission of snail-borne trematode infections in most endemic areas is facilitated by the presence and distribution [6, 7] of these important snail intermediate hosts that provide suitable environment for the development of trematode parasites [8].

    Secondly, poor access to basic infrastructure by most inhabitants living in endemic settings [9] and the limitation of chemotherapy (the main control strategy in Africa) to effectively control the burden of schistosomiasis led to the call for the implementation of integrated control strategies through the incorporation of snail control to achieve the goal of schistosomiasis elimination [3]. More so, the high risk population largely depend on water bodies domiciled by the snail hosts for their daily and economic activities.

    Several studies have been done to unravel the identity of the “supposed enemy” whose influence is of great public health importance and with pronounced burden amongst people living in marginalized settings of the tropic and sub-tropic regions [10,11,12].

    Therefore, it is important to develop the platform that will monitor and identify snail distribution and infected snails, to help improve control efforts of the diseases caused by snail-borne trematodes. Also, a lot of achievements have been recorded in the identification of some snail hosts of medical and veterinary importance using both morphological and molecular approaches [13,14,15,16] and these have provided information that helped improve schistosomiasis control efforts.

    There are continued efforts at improving the development of biomarkers that are effective in differentiating schistosome parasites and also provide insights into factors influencing host-parasites compatibilities on local scales [17, 18].

    Despite all the efforts, it is obvious that more reliable genomic information is required for snail intermediate hosts populations to help improve control programmes [19, 20] particularly in the schistosomiasis endemic regions of Africa. It is imperative to develop tools that will detect and quantify genetic differences and changes in snail populations and also closely monitor the spread of these genetic variants that have the potentials to affect control strategies [21].

    Great tasks lie ahead and more commitment is required to ensuring the elimination of schistosomiasis from endemic regions of Africa.

    Though, snail hosts studies are crucial especially in Africa as we prioritize NTDs elimination but only few studies have established snail hosts differentiation on local scales [15, 22, 23].

    Therefore, it is imperative to provide adequate information on snail host population structure and diversity both on national and continental scales using molecular approaches in order to strengthen control programmes in Africa. Such information is important for reliable decision making and efficient control implementation. This should be a pre-requisite for setting up effective control programmes that will be supported by active surveillance response system in endemic areas especially in sub-Saharan Africa where the disease burden is enormous but control efforts are limited due to poor funding and lack of political will.

    As suggested by Rollinson et al. [24] that a global awareness be raised to provide adequate support for the elimination of schistosomiasis in endemic countries, it is believed that the support will be more effective by updating the genomic status of snail hosts of trematode parasites where available and also establish reliable comprehensive genome identification database where information is lacking across Africa.

    This paper summarize the available information on the progress made in controlling schistosomiasis transmission through snail intermediate hosts studies using molecular approaches and also identify areas where actions are required to be taken for effective integrated control efforts to be achieved in Africa.

    The predominant snail intermediate hosts implicated for transmitting schistosome parasites in Africa is shown in Table 1.

    The male and female adult schistosome worms dwell inside the blood stream of humans. Schistosoma mansoni and S. haematobium are responsible for intestinal schistosomiasis and urinary schistosomiasis respectively [25] (Fig. 1). S. haematobium is located in the venous plexus and it drains the infected person’s urinary bladder while S. mansoni is located in the mesenteric veins and it drains both the large and small instestines.

    Typical life cycle of schistosome parasites [84]

    Schistosome eggs equipped with spines are deposited by the female schistosome parasites into the small venules of the portal and perivesical systems. The eggs migrate towards the bladder and ureter (S. haematobium) and the lumen of the intestine (S. mansoni) and are released into the environment with urine or feces. The accumulation of eggs deposited in the venules cause its blockage and this burst the veins and allows eggs and blood to access the urinary bladder and the intestine and this leads to the characteristic symptom of blood in urine and feces. When the eggs are released into the freshwater bodies, they hatch into miracidia and penetrate a suitable snail intermediate host of the genus Bulinus (with species such as Bulinus truncatus, B. globosus, B. senegalensis, B. forskalii, B. camerunensis, B. africanus and B. tropicus) or Biomphalaria (with species such as Biomphalaria pfeifferi, Bi. Choanomphala, Bi. alexandrina, Bi. sudanica), both serve as snail hosts of S. haematobium and S. mansoni respectively. The schistosome parasites develop and multiply into the infective cercariae within the snail hosts and are released into the water bodies by the snails. Humans become infected when they have contact with waterbodies that are infested with active cercariae [25].

    Figure 2 shows the distribution of schistosomiasis on the African continent [26].

    Distribution of schistosomiasis in Africa [26]

    Tables 2 and 3 shows the identified Bulinus sp. and Biomphalaria sp. and their accession numbers selected from the GenBank. Source: [27]

    Snail molecular studies: identification of snail taxa

    The use of molecular tools in species identification and exploring host-parasite compatibilities has provided answers to complex evolutionary questions over the years. Though, before the advent of molecular methods in differentiating snail hosts, intermediate snail hosts identification were largely done using morphological descriptions such as shell shape, shell size, nature of aperture, observations on the radula and reproductive system to assess taxonomic variations [28, 29]. However, its applications have enhanced the establishment of database platforms to deepen our understanding on snail hosts diversity and population structure [5, 30]. More importantly, its’ usage in differentiating the complex Bulinus group [31] which is the major snail intermediate hosts of S. haematobium, a prominent schistosome parasites causing serious morbidity across Africa especially in sub-Saharan Africa.

    Advances in the production of effective genetic markers such as random amplified polymorphic DNA (RAPDs) ribosomal gene (rRNA), and the mitochondrial cytochrome oxidase I (COI) have created robust and reliable taxonomy [31] which has improve our knowledge on the epidemiology of schistosomiasis [12].

    Though the use of molecular approaches in differentiating snail hosts population structure have been applied on local scales across Africa but it is yet to be fully explored. For instance, [14] identified B. forskalii, Bi. pfeifferi and B. truncatus using molecular methods in N’Djamena, Chad [22]. Comprehensively identified five snail hosts (B. globosus, B. forskalii, Bi. pfeifferi, Lymnaea natalensis and Indoplanorbis exutus) of trematode parasites in Nasarawa State, north central, Nigeria using mitochondrial gene cytochrome oxidase I (cox1). The study assessed the phylogenetic relationship of these snails and established that B. globosus from Nasarawa State, Nigeria clusters with B. globosus sequence data from other West African countries such as Burkina Faso, Senegal and Niger when BLAST, using nucleotide blast homology on genbank forming a monophyletic lineage but forms paraphyletic relationship with B. globosus species from East Africa. B. forskalii also followed similar pattern, as it cluster to form a monophyletic relationship with species from Burkina Faso (Mogtedo barrage), Niger (Tondia) and Senegal (Thiekeene Hulle) while Bi. pfeifferi from Nigeria clustered with Bi. pfeifferi species from Senegal (Lake De Guirs), Kenya (Kibwezi), Uganda (Lake Albert) and Zimbabwe (Chiweshe) to form a monophyletic relationship. Indoplanorbis exutus formed a paraphyletic relationship with species from Asia. Information is lacking on the phylogenic status of Indoplanorbis exutus and Lymnaea natalensis from Africa, there is need to prioritize the establishment of reliable genome database for these snails across Africa considering their veterinary importance. Similarly, [32] characterized Bulinus truncatus using PCR-RFLP technique and assessed their infection status with Dra I gene repeat in Southwest Nigeria while [23] established the population structure of B. globosus, B. forskalii, B. camerunensis and B. senegalensis in schistosomiasis endemic communities of Ogun state, Southwestern Nigeria through the application of PCR-RFLP on the snails ribosomal ITS region.

    Molecular tools application is not limited to elucidating relationships across snail hosts taxa. The application of PCR DraI and sm17 in the early detection of S. haematobium and S. mansoni in infected snail intermediate hosts of the Bulinus sp. and Bi. pfeifferi respectively have helped strengthen snail surveillance and boost schistosomiasis control efforts [33, 34]. Also, the simultaneous usage of PCR, DraI PCR and Sh110 SmSl PCR were effective in differentiating schistosome parasites that infected snails within the Bulinus group in Morocco [35]. Table 4 shows the summary of intermediate snail host studies carried out in different parts of Africa.

    Snail genome studies: implication for effective control programme

    The need to meet the goals of schistosomiasis elimination prompted the pursuit of an integrated control approach [3, 36] and contributions from different stakeholders [31] have provided baseline information and vigor for the pursuit of efficient implementation of control efforts in Africa [15, 37,38,39,40].

    It is observed that environmental factors play significant role in the population size of snail host’s natural populations. The effects of these environmental conditions greatly affect gene flow between populations and induces important variations in population size [29]. Their hermaphroditic capabilities enable self or cross fertilization and allows for different genetic consequences [41]. Also, the fitness impact of parasites on the snail mating systems affects the genetic structure of the snail hosts population [42, 43]. Good understanding of local fluctuation in geographic origin, population size and snail hosts’ reproductive potentials are fundamental to improving our knowledge on the demographic stochasticity of natural population’s genetic structure [43].

    The investigation of snail genetics role in trematode parasite infections variation using molecular approaches is vital to understanding their epidemiology. The assessment of the genetic differentiation of Bulinus snails from different ecological zones across Cameroon, Egypt and Senegal revealed high genetic diversity within Bulinus populations sampled from the three countries with the highest diversity observed within populations of B. forskalii and B. senegalensis [39], but this is contrary to findings on Biomphalaria pfeifferi in Madagascar which was reported to have high level of inter-population variation [44]. Utilizing the use of molecular markers[45], showed that there was high intra-population diversity with high levels of population structure but low level gene flow among populations of Biomphalaria choanomphala along Lake Victoria covering Tanzania, Kenya and Uganda. The study identified consistent parasitism as the major influencing factor [46] indicated that Biomphalaria species of African origin were derived from the neotropical natives and that proto-Biomphalaria glabrata is the progenitor of the African species through the trans-Atlantic colonization of Africa.

    Findings have shown that schistosome parasites development inside the snail host is influenced by both the host and parasite genes [17, 47]. This has increase stakeholders consciousness to unsnarl the schistosome parasites and snail genes that influence this intrinsic association [48, 49]. This led to the development of genetic markers for the identification of resistant genes within the snail hosts. Detailed elucidation of snail hosts population structure and the identification of genetic markers for parasite resistance will further boost the resolve of effective integrated control approach for schistosomiasis elimination in Africa [37]. Observed from investigation on identified refractory strains to S. mansoni in Bi. alexandrina population from Egypt that refractory character within the snail hosts population is hereditary and therefore advised that snails that are actively resistant to schistosome parasites should be cultured to encourage biological control of snail intermediate hosts in a natural population.

    Furthermore, it was established that snail hosts infection with schistosome parasites is species specific and often localized [50], efforts should be made to identify and document snail hosts that have refractory characters across regions. The introduction of snail hosts with parasite resistant genes into the natural population to replace the susceptible snail species in endemic areas will discourage schistosomiasis transmission and also reduce damage to the natural ecosystem through the use of molluscicides.

    More importantly, it is necessary to encourage the extensive study of snail genome differentiation on a large scale due to the current global changes that have led to changes in the modification of the geographical distribution of species prompting hybridization, such hybridization is already known to occur in schistosomes and offspring have been shown to have superior virulence and invasive capacities [51]. This is an emerging public health concern particularly because of the changing geographic distribution of humans, domestic animals and wildlife [52]. Prioritizing snail studies is essential and there is need to update the snail hosts genome library for Africa in order to boost the realization of schistosomiasis elimination through active integrated control mechanisms. This is important because of the dynamic changes in climatic and environmental conditions which play key roles in the distribution of the snail intermediate hosts and the development of schistosome parasites.

    Large-scale assessment of snail intermediate hosts genome will create the platform to determine the degree of variability among and within snail populations across the continent and give an overview of schistosomiasis distribution in Africa with current realities.

    Determination of snail intermediate hosts population genetics and diversity using biomarkers is shown in Fig. 3

    Determination of snail intermediate hosts population genetics and diversity using biomarkers

    Gaps analysis: three research priorities identified

    Though, molecular approaches to differentiating snail intermediate hosts are key to combating the menace of this debilitating disease in Africa [17]. However, studies on snail biology should not be limited to the application of molecular methods because there are other aspects of snail studies that are essential and should be taken seriously.

    Firstly, snail identification using shell morphology and bionomics studies are essential to understanding the distribution pattern of snail hosts and transmission dynamics of schistosomiasis and other disease causing snail-borne trematodes at local scales across the continent [53, 54]. We observed that there is dearth of knowledge and lack of expertise in the area of malacology in Africa, this might be due to lack of interest from individuals as it is believed that the application of molecular methods is more acceptable and efforts are geared towards establishing collaborations that will help access such platforms. However, the knowledge and expertise of snail identification using shell morphology requires highly trained professionals to enhance capacity building due to its importance in disease surveillance and should be prioritized in order to achieve the goal of schistosomiasis elimination in Africa.

    Secondly, the application of Geographical Information System (GIS) and remote sensing technologies to map and define the spatial limits of snail hosts distribution is an important area that requires utmost attention. Though it has been applied in some parts of Africa on local scales [55,56,57], but information on the geospatial distribution of important snail intermediate hosts is lacking in most African countries. Mapping and predicting snail hosts distribution on national and continental scales to establish comprehensive GIS database will help characterize the different eco-zones with relevance to the prevalent diseases, thus provide information that will enhance optimizing the use of available resources [58], and also strengthen the drive for effective schistosomiasis control on the continent.

    Thirdly, there is urgent need to aggresively create awareness by educating the larger society especially people in the endemic areas through the mass media and other communication platforms on the importance of these planorbid snail hosts in schistosomiasis epidemiology. Experience in the field have shown that most locals who live around waterbodies in most endemic settings have little or no knowledge of the snails and are not aware of the danger their presence poses to their well-being. Hence, it is important to consistently create awareness on snail hosts control. The locals should be equipped with information that will spur them to ensuring that the snails does not thrive in their environment and also be mandated to urgently report snail hosts presence in any waterbody around their domain to the relevant health authorities promptly.

    In addition to the aforementioned three gaps on snail biology, there are other areas that requires attention. This includes effort to put infrastructure in place or consistently modify the environment to discourage the continued presence and distribution of snail hosts and schistosomiasis transmission in most endemic countries. The environment in most endemic countries are characterized by factors that influence the distribution of snail hosts of schistosome parasites as a result of poor environmental management [59,60,61,62]. The presence of aquatic plants such as Eichhornia crassipes within and around waterbodies enhance the occurrence, distribution and abundance of snail hosts because it serves as a good source of food, provide shelter and oviposition sites for the snails [63,64,65]. Environmental modification through active removal of aquatic plants and silts from waterbodies renders the habitat unfriendly to the snail hosts [66, 67]. The indiscriminate disposal of human wastes due to lack of sanitary facilities and poor access to potable water sources for domestic purposes also add to the sources of infection in the environment, this facilitates easy access of schistosome parasites in feces or urine from infected persons to waterbodies and snail intermediate hosts.

    Despite the public health significance of schistosomiasis globally especially in Africa where about 95% of global schistosomiasis is concentrated [68, 69], the use of micro-array platforms to decipher the intricate interplay between the parasites and the snail hosts is scarce. There is need for drastic improvement in the application of immunomic and next-generation sequencing platforms regarding schistosomiasis and other NTDs [70,71,72,73,74,75]. Efforts should be geared towards identifying genes that are actively involved in snail’s immune responses in order to initiate defence mechanisms that will block schistosome parasites survival in the snails [76]. Molecular tools application is vital for efficient snail surveillance and has great potential, as it is important for snail hosts and trematode parasites identification and also useful in defining the level of species biodiversity [5, 22, 31, 77] these are pre-requisite to blocking schistosomiasis transmission effectively [78]. The lack of reference laboratories to carry out early diagnosis of schistosomiasis cases on infected people is a big challenge to the pursuit of schistosomiasis elimination in Africa. This debacle also extends to poor or absence of platform for researchers to execute evidence-based research on snail hosts. Such platforms, if available would help strengthen schistosomiasis surveillance and capacity building within the continent.

    The challenge of insufficient supply of praziquantel due to scarcity of funds and the resistance of schistosome parasites to the drug of choice [79] led to the increasing call for the use of molluscicide to curtail snail distribution, but molluscicide application is yet to be substantially utilized in many countries endemic for schistosomiasis in Africa. This is partly due to reliance on prioritized chemotherapy treatment of school-aged children with praziquantel, which is not very effective due to the high re-infection rate few weeks after treatment or due to insensitivity or poor knowledge about snail hosts’ role in schistosomiasis transmission.

    This might also be attributed to the perceived negative impact that niclosamide, the molluscicide of choice have on fishes, an important protein source and means of generating income for people living in rural settings. Therefore, it is advised that the molluscicide formulation be improved to ensure that it has less negative impact on the environment and biodiversity [80], but retain its potency against snail hosts [81].

    The exploration of the molluscicidal properties of plants such as Phytolacca dodencandra and Millettia thonningii and some other plants with similar properties [82] should be considered. The distribution of these molluscicidal plants in areas identified as schistosomiasis hotspots in endemic areas will help curtail the distribution of snail hosts. However, it is important to effectively monitor the plants when cultivated in large scale because of their toxic properties.

    The use of biological techniques for snail hosts control is long overdue in Africa, measures should be taken to effectively apply natural predators or encourage biotechnological methods to induce infecundity in the snails [83]. Figure 4 shows the mechanism for efficient schistosomiasis transmission interruption.

    Watch the video: Fighting bladder snail infestation in my planted tank (December 2021).