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Schistosomiasis (Bilharzia)

Introduction

This is a parasitic worm infection that is acquired by skin contact with fresh water in certain parts of the world. The parasite lives in both humans and fresh water snails.  Infected snails release microscopic infective parasites in to the water. These penetrate the skin of humans who have contact with the water. Currents can spread the parasites to areas well away from the contaminated water.

Infection can occur during swimming, bathing, paddling or undertaking watersports in infested fresh water, or by showering in water drawn directly from fresh water sources - this can occur in lakeside lodges/campsites.

Schistosomiasis occurs in fresh water lakes, ponds, rivers and streams in Africa, South America and parts of the Middle and Far East, particularly Lake Malawi, Lake Victoria and the Nile river.

This map below has been reproduced with permission of and acknowledgement to WHO (World Health Organisation). A full sized version of this map can be accessed by clicking on the map.

Schistosomiasis

The Illness

The initial infection usually produces no symptoms but itchy skin can develop where parasites enter the skin. Sometimes, two to four weeks later, fever, diarrhoea, cough or a rash occur as the parasites move around the body, this is acute schistosomiasis.

The parasites become adult worms after approximately 8-12 weeks inside the human body. They are 0.5-2 cm long and live in the veins around the bladder and bowel for an average of 2-8 years. The female parasite produces microscopic eggs which are passed out of the body in urine and bowel motions. If these enter fresh water they can infect snails and continue the life cycle. It is the eggs that can cause long term symptoms.

Most travellers have no symptoms, but it can cause blood in the urine, pain passing urine, change in the bowel habit, blood in the bowel motions, tummy/pelvic pain or genital lumps or bumps. Years later, long standing disease can lead to damage of the bladder, kidneys, bowel, liver and genital tract.

Diagnosis and Treatment

Oral medication called praziquantel can cure the infection. 

If you have had contact with fresh water in countries where schistosomiasis occurs, you should:

  • Attend your GP no sooner than 8 weeks after exposure even if you have no symptoms.
    • The infection cannot be diagnosed earlier if you have no symptoms.
    • Your GP will send a blood test to check for exposure to the parasite. If it is positive, you will be referred to an Infectious Diseases clinic for further tests and treatment.
  • Attend your GP on return if you have any symptoms of schistosomiasis.
    • Acute schistosomisis can be hard to diagnose, and you may be referred to a local Infectious Diseases clinic for tests.
    • Schistosomiasis is diagnosed by a blood test taken no sooner than 8 weeks after exposure.  If it is positive, you will be referred to an Infectious Diseases clinic for further tests and treatment.

Recommendations for Travellers

The infection is often missed because most infected people don’t have symptoms, but damage can occur years after infection. Because of the potential long term effects of the disease it is therefore recommended that travellers take precautions to prevent infection, rather than rely on treatment.

DOs

  • Check prior to travel if you are visiting countries where schistosomiasis occurs.
  • Swim only in chlorinated swimming pools or safe sea water in affected areas.
  • Check with a reliable source to ensure water facilities (showers, baths etc) at accommodation/recreational facilities are safe (many hotels/facilities draw water directly from nearby lakes, untreated, this water can transmit schistosomiasis).
  • Avoid activities in affected regions that may involve direct water contact, this includes paddling, swimming, diving, snorkelling, rafting, canoeing, water sports etc.
  • Only drink bottled or boiled water.
  • Visit your GP for asessment 8 weeks after return to the UK if you are concerned that you have been exposed, or earlier if you have symptoms. Early treatment stops the risk of long term damage. 

DON'T

  • Buy treatment for schistosomiasis overseas. This is often sold in resorts and may be counterfeit, taken at the wrong dose or taken too early to cure infection – the drug only works when taken at least 8 weeks after exposure.
  • Use insect repellent to prevent infection. There is no evidence that this works and most repellent is water-soluble and so will simply wash off.
  • Rely on vigorous towel drying of skin after water contact – there is no reliable evidence to prove that this works.
  • Rely on other travellers/locals to inform you if a water source is infected or not – try and find out from an official/reliable source.

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