Disease Information Sheets
Schistosomiasis (Bilharzia)
Introduction
Schistosomiasis is a parasitic worm infection acquired through bathing in contaminated water. Although initially there may be no symptoms at all associated with the infection, in the long term it can cause serious illness including bladder cancer, and malnutrition, anaemia and learning difficulties in children. The parasite develops in fresh water snails, exits the snail into the water and then penetrates the skin of people bathing, wading, playing or swimming. Further development occurs in the person’s body, and eventually he or she will start excreting parasite eggs in urine or faeces. If these contaminate fresh water, the parasite can find new snail hosts and the life-cycle starts again.
How common is it?
Schistosomiasis is the parasitic disease with the second greatest impact worldwide (after malaria), with more than 200 million people infected. It is found in tropical and subtropical climates in 78 countries worldwide, although it has been estimated that at least 90% of people requiring treatment live in Africa. Because it is propagated by the contamination of water with human urine and faeces, it is a disease of poor areas that lack safe drinking water and sanitation. Agricultural and fishing populations are particularly affected, as are women doing domestic chores in infected water.
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Countries with high (red) & low (pink) risk of schistosomiasis in either hepatic-intestinal or urinary forms, or both.
Are travellers and/or expat workers at risk?
Yes. If you come into contact with contaminated fresh water, then you are at risk. Paddling, wading, swimming or washing in contaminated rivers, lakes, canals or ponds are risk activities. You may also be infected if you drink unsafe water, as the parasites may enter your body through the mucous membranes of the mouth.
What is the illness?
Most people have no early symptoms, but you may develop a rash or itchy skin within a few days of being infected (“swimmer’s itch”), and you may develop a fever and flu-like illness (“Katayama fever”) within a couple of months. The parasites that penetrate the skin mature into adult worms that sit in the blood vessels supplying the bladder or intestine and produce thousands of eggs. The presence of these eggs causes inflammation, and it is this that causes all the serious long-term illnesses associated with infection, often years later. Signs and symptoms of this chronic inflammation include bleeding into the gut or bladder and urinary or intestinal obstruction. Some eggs do not pass into the gut as they should, and are swept along the blood vessels into the liver, where they lodge. This results in liver pain and swelling, and eventually serious circulatory and breathing problems.
How is it treated?
There are safe and effective drugs for the treatment of schistosomiasis. However it is important to treat the disease before the serious long-term effects develop. If you think you could have contracted schistosomiasis, visit your doctor or travel health clinic for testing.
How can it be prevented?
There is no vaccine available, and no preventative drugs.
Avoid swimming, wading etc. in contaminated fresh water. Chlorination and salt kills the larvae, so well-maintained swimming pools and the sea are fine. Ignore advice from hotels or tourist associations that their local lake/river is safe and has no snails. If you decide to swim or dive in fresh water, bear in mind that your risk will be greatest near the shore - taking a boat to the middle of the lake and diving from there will be safer than diving directly from the shore.
Drink safe water - boil water for a minute or filter it before drinking. Iodine alone will not guarantee that the water is safe and free of all parasites. Boil bath/washing water for at least a minute or heat to 50ºC for 5 minutes. Water held in a storage tank for at least 1-2 days is safe for bathing as the larvae only live for up to 48 hours outside a host.