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.

How you get schistosomiasis

The worms that cause schistosomiasis live in fresh water, such as:

• ponds
• lakes
• rivers
• reservoirs
• canals

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 pee 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.

Symptoms of schistosomiasis

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:

• a high temperature (fever) above 38C
• an itchy, red, blotchy and raised rash
• a cough
• diarrhoea
• muscle and joint pain
• abdominal (tummy) pain
• a general sense of feeling unwell

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.

Long-term problems caused by schistosomiasis

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:

• digestive system can cause anaemia, abdominal pain and swelling, diarrhoea and blood in your poo
• urinary system can cause irritation of the bladder (cystitis), pain when peeing, a frequent need to pee, and blood in your pee
• heart and lungs can cause a persistent cough, wheezing, shortness of breath and coughing up blood
• nervous system or brain can cause seizures (fits), headaches, weakness and numbness in your legs, and dizziness

Without treatment, affected organs can become permanently damaged.

When to seek medical advice

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 finding eggs in a sample of your pee or poo. You may also be diagnosed by a blood test.

Treatments for schistosomiasis

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 a few weeks after you were infected, or repeated again a few weeks after your first dose.

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.

Preventing schistosomiasis

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:

• avoid paddling, swimming and washing in fresh water – only swim in the sea or chlorinated swimming pools
• boil or filter water before drinking – as the parasites could burrow into your lips or mouth if you drink contaminated water
• avoid medicines sold locally that are advertised to treat or prevent schistosomiasis – these are often either fake, substandard, ineffective or not given at the correct dosage
• don't rely on assurances from hotels, tourist boards or similar that a particular stretch of water is safe – there have been reports of some organisations downplaying the risks

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.