Bilharzia, or schistosoma, is a parasitical worm that causes schistosomiasis in humans. Schistosomas are classified as trematodes, or flukes. They are present in bodies of water such as rivers and human reservoirs throughout Africa, Asia and the Caribbean. Overall, bilharzia affects around 200 million people worldwide.
The Parasite
The mode of transmission depends on the presence of snails in the water. The bilharzia parasite hatches from eggs excreted in the stool of infected individuals. The eggs come from people who urinate or defecate in the water, or from runoff from inappropriately treated public waters. The motile larvae that emerge from the eggs infect the snails, where they mature. Afterward, they emerge from the snails and infect humans, repeating the cycle.
Transmission
The initial point of entry of the parasite is through the skin. When going though the skin, the parasite can cause a local reaction, producing itching and a raised, red rash, called cercarial dermatitis.
Illness
After the parasites enter a human host, they go through the blood stream into the lungs. From there, they travel via the venous systems to different parts of the body. A few weeks after exposure, the parasites cause a non-specific illness with fever, generalized body aches, nausea and vomiting, and abdominal pain.
Complications
If the number of worms infecting the individual initially is large enough, it can cause diarrhea, enlargement of the liver, and inflammation of the colon and the bladder. In the bladder, the infection can lead to blood in the urine, and predispose patients to bladder cancer. The lungs can also be affected. Some species of schistosoma can invade the spinal cord and the brain, creating granulomas (small areas of inflammation) that can lead to seizures or strokes.
Repeated exposure and reinfection can occur in children. This can result in learning disabilities, anemia and malnutrition.
Diagnosis
There is a blood test to detect the presence of bilharzia in the blood. This test takes time, so patients usually are treated if they have the signs and symptoms of schistosomiasis and a history of recent travel to an endemic area.
Treatment/Prevention
Treatment of bilharzia infection is with praziquantel. The initial treatment only lasts one or two days. This drug does not kill worms in the process of growth, so it needs to be repeated one to two months later. Dizziness, nausea, vomiting and abdominal cramps are common side effects of praziquantel.
The main preventive strategy is to not swim or wade into bodies of water that may be infested with bilharzia. Other strategies include boiling drinking water and heating bath water to about 150 degrees F for five minutes.
References
- Red Book: 2009 Report of the Committee on Infectious Diseases, American Academy of Pediatrics Committee on Infectious Diseases, 2009
- Centers for Disease Control and Prevention
