Schistosomiasis

Schistosomiasis, also known as bilharzia (bill-HAR-zi-a), is a slowly progressive disease that is increasing in incidence worldwide. It is most prevalent in agricultural areas in Asia, Africa, and South America.

The degree of infection determines the intensity of illness. If untreated, significant morbidity and even mortality can result.

Causes

Schistosomiasis is caused by blood flukes of the class Trematoda. Three major types of these parasites exist: Schistosoma mansoni and S.japonicum infect the intestinal tract; S. haematobium infects the urinary tract.

These cercariae penetrate the skin or mucous membranes and eventually work their way to the liver's venous portal circulation. There, they mature in 1 to 3 months. The adults then migrate to other parts of the body.

The female cercariae lay spiny eggs in blood vessels surrounding the large intestine or bladder. After penetrating the mucosa of these organs, the eggs are excreted in stool or urine. If the eggs hatch in fresh water, the first-stage larvae (miracidia) penetrate fresh­water snails, which act as passive intermediate hosts. Cercariae produced in snails escape into water and begin a new life cycle.

The parasite is transmitted through bathing, swimming, wading, or working in water contaminated with Schistosoma larvae, which are known as cercariae during their infective stage.

Signs and symptoms

Within days after becoming infected, you may develop a rash or itchy skin. Fever, chills, cough, and muscle aches can begin within 1-2 months of infection. Most people have no symptoms at this early phase of infection.

Eggs travel to the liver or pass into the intestine or bladder. For people who are repeatedly infected for many years, the parasite can damage the liver, intestines, lungs, and bladder.

Diagnostic tests 

The presence of ova in the urine or stool or a mucosal lesion biopsy confirms the diagnosis. A white blood cell count shows eosinophilia.

Treatment

Safe and effective oral drugs are available for the treatment of schistosomiasis. Praziquantel is the drug of choice for all species of Schistosoma. Travelers should be advised to contact an infectious disease or tropical medicine specialist. You will be given pills to take for 1-2 days. I've taken the cure myself and it is relatively painless.

Prevention

• Avoid swimming or bathing in water known to be contaminated or potentially contaminated
• Avoid bodies of water of unknown safety
• Eradication of snails (an intermediate host for the parasite) in areas used by humans.