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You’re back from safari but you seem to always be tired, can’t concentrate, and feel listless and sleepy. Your wife is fed up and you can’t make it through meetings at work without snoring. Remember cooling off in the Zambezi while your PH kept the crocs away with his .375 magnum? Remember walking through that stream while tracking that trophy dagga boy? Good news, bud: it is not only because you miss Africa and that you are way over 40 that you are feeling this way.

When your PH slapped you on your back and said that Africa becomes part of you, he meant it literally and figuratively: Africa is not only in your heart - you could be harbouring Africa’s common water-bourne parasite in your bloodstream.

The African bush is a place of beauty, tranquility and magnificence but is also home to some of the worlds most deadly diseases. One of them, lurking in streams, rivers and pools has a dark side to it which could cause life-threatening complications. It is a common, chronically debilitating and potentially lethal disease affecting an estimated 200 million people, half of whom live in Africa, with 600 million people being at risk.

It is called Bilharzia or Schistosomiasis.

Schistosomiasis is most prevalent in sub-Saharan Africa. This infection occurs throughout the tropics and sub tropics. It is endemic to 74 countries. Bilharzia is a parasitic infection caused by Schistosoma blood flukes.

Five species of Schistosoma infect humans:

Schistosoma mansoni and Schistosoma intercalatum cause intestinal schistosomiasis

Schistosoma haematobium causes urinary schistosomiasis

Schistosoma japonicum and Schistosoma mekongi cause Asian intestinal schistosomiasis

Shistosoma flukes have a complex life cycles involving specific freshwater snail species as intermediate hosts. Bilharzia eggs are released into the environment from infected individuals, hatching on contact with fresh water to release free-swimming miracidium.

Miracidia infect fresh-water snails by penetrating the snail’s foot.

Infected snails release large numbers of small, larvae called cercariae, capable of penetrating the unbroken skin of humans. Even brief exposure to contaminated water can result in infection.

Cercariae emerge constantly from the snail host in what is called a circadian rhythm. This is dependent on ambient temperature and light. Cercariae are highly mobile and can sink to maintain their position in the water or swim upwards if stimulated by water turbulence, shadows and by some chemical substances found on human skin.

Cercariae secrete enzymes that break down human skin and make penetration possible. "Swimmers itch" occurs 1 day after penetration. It is an itchy rash caused by the death of cercariae upon skin penetration. The rash resolves spontaneously within 10 days and is rare in endemic areas.

Free-swimming Miracidia which enter the snail by penetrating the snail’s foot.

As the cercaria penetrates the skin it transforms into a migrating schistosomulum stage. Here it stays in the skin for a few days while locating a small vein to transport it to the lungs of the human host. From here migration to the liver takes place.

Juvenile worms from some species develop oral suckers and the worms start feeding on red blood cells. Worms pair up and:

S. mansoni and S. japonicum relocate to the intestine or rectal veins

S. haematobium migrate from the liver to the venous plexus of the bladder, ureters, and kidneys.

Worms reach maturity in eight weeks, at which time they begin to produce eggs. Adult worms may produce 300 to 3000 eggs per day. Many of the eggs pass through the intestinal or bladder wall into the feaces or urine.

Some eggs released by the worm pairs become trapped in the veins, or will be washed back into the liver, where they will become lodged. Worm pairs can live in the body for an average of four and a half years, but may persist up to 20 years.

Trapped eggs mature normally, and elicit a vigorous immune response. The eggs themselves do not damage the body but due to the immune response severe complications may arise.

Skin vesicles on the foot, created by the penetration of Schistosoma


Schistosomiasis is a chronic disease. Many infections are asymptomatic, with mild anemia and malnutrition being common in endemic areas. Katayama fever however is a rare but potentially lethal illness occurring 1 to 3 months after the primary infection.

Symptoms include, fever, headache, chills, sweating, diarrhoea, cough, enlarged liver and glands and urticaria.

Clinical features of chronic Bilharzia include, fatigue, abdominal pain, cough and diarrhoea. Various systems can be involved.

Lung disease: Fatigue, dizzyness and chestpain may develop due to embolizing eggs.

Liver disease: Abdominal distension, enlarged liver, fluid accumulation in the abdomen, dilated bloodvessels in the oesophagus.

Intestinal disease: Embolizing eggs may cause chronic inflamation of the large bowel, bloody diarrhoea, anemia and rectal prolapse

Central nervous system disease: Epilepsy, paraplegia and bladder dysfunction.

Typhoid bacteria may colonize the adult worms providing a source of recurrent typhoid attacks.

CLICK HERE to watch the Wellcome animation

Diagnosis of Bilharzia is usually confirmed by serologic studies (a blood test) or by finding Bilharzia eggs on microscopic examination of stool or urine.

Bilharzia eggs can be found as soon as 6-8 weeks after exposure, but are not always detectable. Blood test in the exposed, asymptomatic traveler should ideally be performed 6-8 months following exposure.

Safe and effective drugs are available for the treatment of Bilharzia and your health care worker or Family physician will prescribe medication which will kill the adult Bilharzia worms.

How can I prevent Schistosomiasis?

Avoid swimming or walking in freshwater in countries in which schistosomiasis occurs.

Drink safe water.
You should either boil water for 1 minute or filter water before drinking it. Boiling water for at least 1 minute will kill any harmful parasites, bacteria, or viruses present. Iodine treatment alone will not guarantee that water is safe and free of all parasites.

Heat your bath water for 5 minutes at 150°F. Water held in a storage tank for at least 48 hours should be safe for showering.

Dr. Swart has been involved in Communicable disease control since 2004 and is an authority on Malaria, tropical and infectious diseases in Africa.

Vigorous towel drying after an accidental, very brief water exposure may help to prevent the Schistosoma parasite from penetrating the skin.
You should NOT rely on vigorous towel drying to prevent Bilharzia.

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