Schistosomiasis, also known as Bilharzia or Katayama fever, is a parasitic infection caused by the parasite schistosoma. There are five species of schistosoma that can infect humans and these species are endemic in tropical and subtropical areas. Africa bears the largest disease burden and children under 14 years old are most commonly affected. Freshwater snails are the intermediate host of the parasite. Exposure to contaminated fresh water is necessary for infection. Control of the schistosomiasis disease burden is often focused around control and removal of the freshwater snail intermediate species.
S. mansoni and S. haematobium are found in Africa. S. haematobium is the only species found in the Middle East. S. japonicum is endemic in Indonesia, China, and Southeast Asia. S. mekongi is found in Cambodia and Laos, and S. intercalatum, can be found in Central and West Africa.
Stages of infection
- Immediate - occurs hours to days after infection and is characterized by a maculopapular rash that is caused by parasite penetration through the skin. This infection is similar to swimmer’s itch, which occurs when non-human infecting species of Schistosomiasis penetrate the skin.
- Acute - occurs days to month after infection. Symptoms are fever, headache, generalized myalgias, bloody diarrhea, RUQ pain, and/or respiratory symptoms. On physical exam patients have tender hepatomegaly and splenomegaly. CBC often shows eosinophilia. CXR can show evidence of interstitial pneumonitis.
- Chronic - occurs months to years after initial infection and is caused by a granulomatous reaction to schistosoma eggs.
- GI/Liver - patients can develop ulceration or microabscess of the bowel and periportal fibrosis in the liver. Symptoms include alternating diarrhea and constipation, fecal occult blood, hepatomegaly and splenomegaly.
- GU - specifically from infection by S. haematobium. Symptoms include dysuria and hematuria.
- CNS - mechanism of egg deposition is unknown. Symptoms include seizures and transverse myelitis.
Gold standard is examination of the urine or stool for evidence of eggs. Serology testing can be used however it does not distinguish between a current and past infection.
Praziquantal, an antihelmithic medication, which acts by killing adult worms, is the treatment of choice. Dosing is 20mg/kg x2 doses given four hours apart. If infection occurs in Southeast Asia, current recommendations are to take 30mg/kg x2 doses given four hours apart. If there is concern that a patient is early in their infection course, you should repeat the dosing several weeks later in order to kill all adult worms.
Written by Grace Lagasse, MD