Schistosomiasis, also known as bilharzia, is an infection caused by a parasitic worm that lives in fresh water in subtropical and tropical regions.
The parasite is most commonly found throughout Africa, but also lives in parts of South America, the Caribbean, the Middle East and Asia. The Travel Health Pro website has a map of where schistosomiasis is found.
You often don't have any symptoms when you first become infected with schistosomiasis, but the parasite can remain in the body for many years and cause damage to organs such as the bladder, kidneys and liver.
The infection can be easily treated with a short course of medicine, so see your GP if you think you might have it.
The worms that cause schistosomiasis live in fresh water, such as:
Showers that take unfiltered water directly from lakes or rivers may also spread the infection, but the worms aren't found in the sea, chlorinated swimming pools or properly treated water supplies.
You can become infected if you come into contact with contaminated water – for example, when paddling, swimming or washing – and the tiny worms burrow into your skin. Once in your body, the worms move through your blood to areas such as the liver and bowel.
After a few weeks, the worms start to lay eggs. Some eggs remain inside the body and are attacked by the immune system, while some are passed out in the person's urine or poo. Without treatment, the worms can keep laying eggs for several years.
If the eggs pass out of the body into water, they release tiny larvae that need to grow inside freshwater snails for a few weeks before they're able to infect another person. This means it's not possible to catch the infection from someone else who has it.
Many people with schistosomiasis don't have any symptoms, or don't experience any for several months or even years.
You probably won't notice that you've been infected, although occasionally people get small, itchy red bumps on their skin for a few days where the worms burrowed in.
After a few weeks, some people develop:
These symptoms, known as acute schistosomiasis, often get better by themselves within a few weeks. But it's still important to get treated because the parasite can remain in your body and lead to long-term problems (see below).
Some people with schistosomiasis, regardless of whether they had any initial symptoms or not, eventually develop more serious problems in parts of the body the eggs have travelled to.
This is known as chronic schistosomiasis.
Chronic schistosomiasis can include a range of symptoms and problems, depending on the exact area that's infected. For example, an infection in the:
Without treatment, affected organs can become permanently damaged.
Visit your GP if you develop the symptoms above and you've travelled in parts of the world where schistosomiasis is found, or if you're concerned that you may have been exposed to the parasites while travelling.
Tell your GP about your travel history and whether you think you may have been exposed to potentially contaminated water.
If your GP suspects schistosomiasis, they may refer you to an expert in tropical diseases. The diagnosis is usually made by testing a sample of your blood. In some cases, eggs may be seen in a sample or your urine or poo.
Schistosomiasis can usually be treated successfully with a short course of a medication called praziquantel, that kills the worms.
Praziquantel is most effective once the worms have grown a bit, so treatment may be delayed until eight weeks after you were infected, or repeated again after this time.
Steroid medication can also be used to help relieve the symptoms of acute schistosomiasis, or symptoms caused by damage to the brain or nervous system.
There's no vaccine for schistosomiasis, so it's important to be aware of the risks and take precautions to avoid exposure to contaminated water.
You can check whether the area you're visiting is known to have a problem with schistosomiasis using Travel Health Pro's country information section.
If you're visiting one of these areas:
Applying insect repellent to your skin or quickly drying yourself with a towel after getting out of the water aren't reliable ways of preventing infection, although it's a good idea to dry yourself as soon as possible if you're accidentally exposed to potentially contaminated water.
There's some evidence that applying insect repellent containing 50% DEET to exposed areas each night after showering kills the parasite in the skin before it moves deeper into the body.