Disease

Scanning electron microscope image of a blood fluke

Scanning electron microscope image of a Schistosoma flatworm, the parasite that causes schistosomiasis.

Biomphalaria snails play a key role in the transmission of intestinal schistosomiasis.

The disease is:

  • parasitic, affecting humans and other mammals
  • caused primarily by the flatworm Schistosoma mansoni
  • found throughout Africa, the Caribbean and South America
  • caught via contact with freshwater that is contaminated with larval forms of the parasite


Role of Biomphalaria in intestinal schistosomiasis transmission

The Schistosoma parasite has a very interesting life cycle:

  • Completion of the sexual phase requires a mammal (for example, humans).
  • It also needs to pass through a certain type of snail, where it undergoes asexual reproduction.

The snails have to be from the genus Biomphalaria and in East Africa B. choanomphala is particularly important. Their necessity for the parasite's life cycle means the distribution of the disease can be very accurately linked to the distribution of these snails.

In certain parts of East Africa, such as Lake Victoria, B. choanomphala snails are known to be the most effective host for the parasite. Habitats where these snails can be found often pose the highest risk for humans to contract the disease.

Due to the lack of facilities, people are often forced to wash clothes, bathe and collect cooking water directly from Lake Victoria. The gentle rocky shore of the lake, interspersed with aquatic plants, is a perfect B. choanomphala habitat and therefore these people are likely to be at very high risk of infection.

Current research, at the Natural History Museum and elsewhere, is looking in more detail at the distribution of B. choanomphala, and seeing whether we can use variables such as water chemistry and temperature to predict their distribution. If so, this will help us provide treatment and education about schistosomiasis to communities that appear to be most at risk.

  • Collection of shells of species involved in the life cycle of Schistosoma blood flukes
    Disease control

    Learn how thinking has changed since a failed attempt in the 1980s to control schistosomiasis by wiping out host snails, and potential ways the problem could be tackled while still maintaining mollusc diversity.