Schistosomiasis

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An estimated 200 million people and many more domestic animals throughout the tropical and sub-tropical world suffer from the parasitic disease schistosomiasis (also known as bilharzia), while more than 400 million others are at risk of infection.

With the aid of cinemicrography, electron micrographs and graphics, this video gives a highly detailed account of each stage in the life-cycle of 'Schistosoma mansoni', one of the five principal species of schistosome and shows how certain characteristic features of the life-cycle of schistosomes help explain the failure to devise any effective vaccine against human schistosomiasis to date.

(00:00) The narrator explains that this video is based on the work of two research teams, one led by Dr Owen Standon at the Wellcome Laboratories of Tropical Medicine in the early 1950s, and the other led by Dr Diane McLaren in the 1980s at the National Institute for Medical Research. Dr McLaren's team used electron micrographs to study the schistosomes. Examples of magnifications are shown. Children are shown playing in water in Africa, and the narrator says that there is a good chance that the water is infected with parasites. A photograph of a boy with Bilharzia (Schistosomiasis) is shown. A male and female schistosome couple is shown. They are also shown through the vein wall of a hamster.

The earliest known recordings of the disease date from 1900BC in Egypt, and 3000-year-old mummies have been discovered with eggs inside them. The history of research into the disease is described. The main species of schistosome that affect humans are described. A world maps shows where the disease is endemic. The narrator explains that water snails play a large part in spreading the disease because they host the parasite before the parasites enter humans. However, killing snails to prevent the parasites spreading is difficult as they are hermaphrodites; only one snail needs to survive to breed.

There is an effective drug treatment, Praziquantel, which has a high cure rate. Other methods of control, such as preventing contamination of water supplies, are described.

(09:04) A water pump that provides clean water is shown. Posters and leaflets used to raise awareness of the disease are shown. The narrator explains that current research is directed at finding a vaccine for the parasitic disease. The life cycle of a schistosome is described from laying eggs, to hatching, to finding a snail host.

(18:07) The description of the life cycle of a schistosome continues. The parasites develop and escape from the snail and penetrate the skin of the new host. An example is shown using a mouse. Once in the body, the egg laying begins again. Some observations of schistosomes follow, including the physical transitions they make as they change from free-swimming organisms to parasites in the body. The reaction of the host to the parasite is also described. The narrator sums up the information given in the film and repeats that hopefully new research will lead to a vaccine preventing schistosomiasis.

Credits: Made by Douglas Fisher Productions for the Wellcome Trust.

Written by Dr. L.G. Goodwin, F.R.S., and Dr. Diane J. McLaren (National Institute for Medical Research, Mill Hill, London), directed and photographed by Douglas Fisher and narrated by Barry Paine.

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