What is Schistosomiasis and Where Is It Found?

The disease isn't found in the U.S., but it's extremely common worldwide

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Schistosomiasis is a disease caused by the larvae of a small, flat worm found in freshwater lakes. The larvae, which normally mature in snails that also live in those lakes, enter through your skin as you swim or bathe in the lake.

The worms that cause the disease aren't found in the United States, but it's a very common disease worldwide, infecting some 240 million people every year. It affects more people than any parasite other than malaria.

It is found in 70 countries, and is also called bilharzia or bilharziasis.

It is a disease that has had substantial impacts—it may have even increased the spread of HIV and hepatitis C.

What Exactly Is Schistosomiasis?

Schistosomiasis is a disease in humans, but it is just one step in the life cycle of the schistosoma worm. These worms require more than just humans for their life cycle; they require fresh water lakes and ponds with snails, as well as incomplete human sanitation.

The schistosome eggs are contained in human stool or urine, and are deposited in lakes where people do not have sufficient sanitation. These eggs hatch, and then in the next stage of development they live within the snails in the lake.

Larvae later emerge from the snails and spread into the water, where they will find a person who wades into the water. The larvae directly penetrate the person's skin, entering into their bloodstream.

They then pass through the lungs and other parts of the body until they land where they lay eggs, and the cycle begins again.

There are different types of Schistosomiasis caused by different species of the fluke. S. mansoni, S. haematobium, and S. japonicum cause the most disease. S. intercalatum and S.

 mekongi are less common.

S. mansoni is the most common, infecting over 80 million people worldwide. It is found in multiple areas in South America, the Caribbean, Africa, and the Middle East, and can cause severe damage to the liver. S. haematobium eggs are laid in the bladder or in female genital tract. It causes blood in the urine and can cause scarring where eggs are laid. It is found in Africa, in the Middle East, and in Corscia, France.

S. japonicum is found in China, the Philippines, and other parts of South East Asia, but despite its name, is very rare in Japan. It infects the liver and intestines, but in rare cases also can infect the brain, leading to seizures and neurological effects. S. intercalatum is found particularly in the Democratic Republic of the Congo and Cameroon. Its prevalence is dropping. It can cause bloody stool and an enlarged spleen. 

S. mekongi is similar to S. japonicum, but it is found along the Mekong River, especially in Cambodia and Laos.

Symptoms of Schistosomiasis

Some people feel itchy where the larvae enter the skin.

Others don't feel anything until several weeks later. Symptoms can include an itchy rash, fevers, a dry cough, and blood in the urine.

It's possible to develop Katayama syndrome (another name for schistosomiasis infection) two to 12 weeks after their first exposure to S. mansoni or S. japonicum. As the immature schistosome worm (schistosomula) first travels through the blood stream and then egg laying begins, some people develop fevers at night, cough (as the worms through the lungs), muscle aches, headache, and other pains.

In infections from the schistosoma species that travel into the veins around the liver, the person may experience an increased risk of cirrhosis of the liver and other liver problems, including liver cancer and colorectal cancer.S. haematobium travels to the bladder, but also can cause genital lesions in women. This is associated with increased risk of bladder cancer.

Schistosomiasis Treatment

There are drugs, like praziquantel, that can effectively treat the infection. However, the disease is often found late, when it already has damaged the liver or other organs, and that damage can't be undone.

It's also possible to be reinfected, and the worms and their eggs can persist for a long time.

Unfortunately, in many places where schistosomiasis is common, the resources for medical treatment aren't available. It is a disease of poverty—of people who don't have full waste sanitation. The effects are pretty substantial for the communities affected.

In some communities, most children become infected with schistosomiasis, which is associated with anemia, as well as growth stunting and other developmental effects.

These infections can be an important cause of disease in communities. S. haematobium leads to bladder scarring which increases pressure on and damages kidneys. It is also associated with bladder cancer. It is also associated with infertility. The late effects on the liver (and portal blood system) and the bladder and kidneys can be substantial for older members of a community.

The immature worms can get lost in the body. Some cause substantial lung problems. Others can get trapped in the brain and can cause paralysis, speech problems, and seizures.

More importantly, the genital lesions from S. haematobium and other schistosomiasis infections may place women at increased risk for acquiring HIV. In addition, Egypt has the highest rates of hepatitis C worldwide, which was thought to have been spread in part by dirty needles used in an anti-schistosomiasis campaign.

Sources:

Bustinduy AL et al. Expanding Praziquantel (PZQ) Access beyond Mass Drug Administration Programs: Paving a Way Forward for a Pediatric PZQ Formulation for Schistosomiasis. PLoS Neglected Tropical Diseases. 2016 Sep 22;10(9):e0004946.

Centers for Disease Control and Prevention. Parasites: Schistosomiasis fact sheet.

Kapoor S. Katayama syndrome in patients with schistosomiasis. Asian Pacific Journal of Tropical Biomedicine. 2014 Mar;4(3):244.

Kjetland EF et al. The first community-based report on the effect of genital Schistosoma haematobium infection on female fertility. Fertility and Sterility. 2010 Sep;94(4):1551-3.

Mekonnen Z et al. Schistosoma mansoni infection and undernutrition among school age children in Fincha'a sugar estate, rural part of West Ethiopia. BMC Research Notes. 2014 Oct 27;7:763.

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