Schistosomiasis is a parasitic illness, which goes by several names, including bilharziasis and snail fever. It has been around since Egyptian times, mummies have actually been found with calcified eggs – dating back to 1500 BC. It is caused by one of five species of water borne flatworms, also called flukes. Fresh water snails are essential for part of the developmental stage of this parasite. The stage that causes human disease is called a cercaria. these are tiny, free swimming, pear shaped tadpole like objects. The cerceraie are stimulated by bright lights and warm day time temperatures, causing them to abandon their snail hosts and look for humans.
Survival time in the water is only 48 hours, so a human host is essential. The oily secretions of human skin attracts them to attach to the skin, they then release a substance that causes the ‘cement’ like substance that holds cells together to split, allowing the cercariae to burrow themselves into your body.
Penetration of intact skin takes between 30 seconds and 10 minutes, initial response is an itchy, rash – which may last for 1-2 days; this is usually followed by a period of six weeks during which worms enter the circulatory system and migrate to the veins of the abdominal cavity, where they reach sexual maturity and release eggs.
These eggs penetrate the walls of certain organs causing bleeding and obstruction. Over time this could leads to a chronic, disabling disease that can be fatal. Other symptoms that may be present include – fever (snail or safari fever), fatigue, loss of appetite, liver enlargement, cough and diarrhea. According to the WHO, in some African countries bladder cancer linked to the schistome is 32 times higher than that of simple bladder cancer in the US.
This incidence of disease is increasing among travelers, due to the increase in “off track” tourism. Infections in travelers are usually acquired by bathing, swimming, wading in infected waters, and also from drinking water. In a lot of these affected countries, local inhabitants swim, wash clothing and drink this very same water. Contaminated waters may include fresh water – lakes, streams – especially along the margins and slow moving waters. Risk is also increased in ditches and swimming pools that are inadequately chlorinated; also implicated is tap water that has been contaminated due to inadequate treatment or contamination.
Schistosomiasis is endemic in almost all of Africa, parts of SE Asia, parts of South America and some Caribbean islands. This affects 200 million people worldwide, out of this 1 million deaths can be attributed to it. Most human infections are caused by 3 species – Schistosomiasis Mansoni (53 countries in Africa, Eastern Mediterranean, Caribbean and S. America.)
Schistosomiasis Japonicum is endemic in seven countries in SE Asia and Western Pacific region. Schistosomiasis Haematobium is endemic in 54 countries in Africa and Eastern Mediterranean.
Diagnosis is usually by finding eggs of the parasite in urine or stool specimens. Prevention is by reducing the contamination of water. Worldwide demand for water has and is increasing; this requires more irrigation projects. Dams that are built for this purpose have been a big factor in causing spread of the disease. Almost half of the egyptian population is infected. The building of the Aswan Dam caused the propagation of S. Mansoni which causes schistosomiasis. W. Africa has seen a tremendous increase in infected persons around man made lakes.
Avoidance of contaminated water is the rule, but in case of exposure, studies have shown that using DEET (the mosquito repellant) can repel the cercariae. Vigorously wipe yourself with rubbing alcohol after exposure, has been suggested.