Schistosomiasis Snail Infection And How It Affects Man

Schistosomiasis Snail Infection And How It Affects Man
Schistosomiasis Snail Infection And How It Affects Man

Have you ever wondered if there’s anything like Snail infection during the course of rearing snails?

On the other hand, have you also thought if all snails are edible? Or you just pick snails for consumption assuming that all snails are healthy and nutritious?

Well here is a shocker; NOT ALL SNAILS ARE EDIBLE.  There are snails that host parasites that are transmitted to human beings directly and indirectly by snail infections in animals.

Handling and cooking of snails require extra care to avoid any health problems. If you are not sure of the specie, it’s better to avoid them totally (touching and eating).

In this resource, we would be discussing the most common snail infection and disease —Schistosomiasis.

Schistosomiasis also referred to as bilharzias, is a parasitic disease caused by the trematode worms (blood flukes) of the genus Schistosoma. It is the second most prevalent tropical disease after malaria and is a leading cause of death in many parts of the globe, and especially Africa where there are occurrences in over 40 countries in the continent. Nearly 192 million people are infected with the disease making Africa the most prevalent continent for schistosomiasis in the world.

A Freshwater Snail Host of Schistosome
A Freshwater Snail Host of Schistosome

Most human infections result from three species out of the six available species and they are Shaematobium, Smansoni and Sjaponicum.

The Shaematobium, which is the causative agent of urogenital schistosomiasis and Smansoni, which causes the intestinal form of the disease are the two species widely spread across Africa.

For instance in The Gambia, urogenital schistosomiasis is endemic in the eastern regions (Central River and Upper River Regions) of the country during the rainy season as a result of seasonal laterite pools formed in cuirasse depressions and few occurrences of the intestinal form of the disease.

Freshwater snails are hosts to the Schistosome parasites where they develop to the infective larval stage for human infection.

Snails of the genus Bulinus are the intermediate hosts of Shaematobium (causing urogenital schistosomiasis) while those of the genus Biomphalaria are the intermediate hosts of Smansoni (causing intestinal schistosomiasis).

These snails occur in most parts of the African continent.

The three other schistosome species belonging to the Shaematobium group (SbovisScurassoniSmattheei) in Sub-Saharan Africa are known to cause animal schistosomiasis in domestic livestock.

These schistosomes also use Bulinus snails as intermediate hosts and they overlap with Shaematobium in some endemic regions.

Schistosomiases in livestock such as cattle, sheep and goat also have potential impact on animal health and productivity. Either way, this disease gets through to human.

Schistosomiasis In A Snail Host
Schistosomiasis In A Snail Host

Identification Of Infected Snails

Identification and detection of schistosome infection in snails is an important aspect of transmission surveillance and a very necessary in unraveling the epidemiology of the disease in the prone endemic regions.

The cercarial shedding method in snails is still the best way to detect schistosome infection, but more rapid and direct techniques have been developed over the years and used as a complement to this long-standing traditional method.

These include simple approaches like the dot hybridisation and antibody detection methods.

Detection in the Bulinus snails is more complicated as they are known to carry different schistosome species necessitating the recent development of a molecular xenomonitoring PCR-based technique that can detect and differentially identify Shaematobium and Sbovis infections in Bulinus snails.

Transmission Of Schistosomiasis From Snail To Man

Schistosomiasis can be transmitted majorly via water bodies as certain freshwater snails are their host.

The infectious form of the parasite, known as cercariae, emerges from the snail into the water bodies such as rivers, lakes, streams etc.

Swimming and drinking of contaminated water are the major ways of transmission however; eating of infected animals is another way.

Man can become infected when the skin comes in contact with contaminated freshwater.

Diagnosis Of Schistosomiasis In Man

Stool or urine samples are examined through the microscope for parasite eggs (stool for S. mansoni or S. japonicum eggs and urine for S. haematobium eggs).

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.

An Infected Skin With Schistosome
An Infected Skin With Schistosome

Treatment Of Schistosomiasis In Man

There is no vaccination for schistosomiasis however, safe and effective medication is available for treatment of both urinary and intestinal schistosomiasis.

Praziquantel, a prescription medication, is taken for 1-2 days to treat infections caused by all schistosome species. DO NOT INDULGE IN SELF MEDICATION!

Prevention Of Schistosomiasis In Snails

Maintaining high hygienic standards in snail farms no matter the size will reduce the outbreak and spread of diseases in the snail farms.

Poor hygiene may predispose the snails to diseases and pathogens, which will affect their growth and reproduction.

The soil must be changed every two weeks and the snail pen cleaned before bringing in fresh treated soil into the snail house.

Walker et al., (1999), opined that snails ingest micro-organisms e.g. bacteria from the soil and their environment.

Prevention And Control Of Schistosomiasis In Man

The best way to prevent schistosomiasis is to take precautions noting that there are no vaccines.

Observing the following are ways of preventing transmission:

  1. Avoid swimming or wading in freshwater bodies of regions where schistosomiasis occurs. Swimming in the ocean and in chlorinated swimming pools is safe.
  2. Only drink safe potable water. If the mouth or lips come in contact with water containing the parasites, one is at risk of getting infected. When there are no other options, its best to bring your water to a rolling boil for at least 1 minute to kill any harmful parasites, bacteria, or viruses present. Iodine treatment alone WILL NOT GUARANTEE that water is safe and free of all parasites.
  3. Water to be used for bathing should also be brought to a rolling boil for 1 minute to kill any cercariae, and then cooled before bathing to avoid scalding. Water held in a storage tank for at least 1 – 2 days should be safe from snail infections for bathing.

    Clean Potable Water To Prevent Snail Infection
    Clean Potable Water To Prevent Snail Infection
  4. Elimination of species hosting snails should be done and mass drug treatment of the entire community is also encouraged. Infected animals should also be treated and prevented from coming across contaminated water.
  5. Chemicals can be used in water bodies frequently to eliminate the snails. This is however not totally safe for other water organisms. Snails can return to the water body if treatment is discontinued.

It is important for those who have had contact with potentially contaminated water overseas to visit their health care provider upon returning to discuss testing.

Conclusion

Snails are healthy, nutritious and friendly animals. However, there are some species that are not edible and harmful to man and animals due to snail infections.

In snail farming, it is important to take adequate care of the snails to avoid diseases and snail infections.

Schistosomiasis Snail Infection And How It Affects Man
Schistosomiasis Snail Infection And How It Affects Man

When handling or cooking snails, it is important to take extra care to prevent transmitting snail infections to man upon consumption. When in doubt of the snail specie, it is best to stay away!

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