Schistosomiasis is a parasitic disease caused by worms called blood flukes. It is often spread through poor personal hygiene or exposure to water contaminated with the parasite Schistosoma, such as during farming or fishing. The disease is endemic or prevalent in various places across Luzon (especially Cagayan province), Visayas (especially Samar and Leyte islands), and Mindanao.

In the Philippines, the disease is caused by the blood fluke Schistosoma japonicum, which is often found in freshwater snails. These worms are able to penetrate human skin when a person comes into contact with water that has infected snails. Once the worms enter the skin, they settle in blood vessels surrounding the intestines, the liver, and the spleen where they lay their eggs. These eggs can then penetrate the intestines and are excreted in the feces of an infected person. Other species of blood fluke are more common in different parts of the world, like Schistosoma haematobium in the Middle East and Schistosoma mansoni in parts of Africa and South America.

Most individuals develop symptoms only months or even years after infection. Symptoms mostly depend on the species of blood fluke and where in the body the fluke lays most of its eggs. Schistosoma japonicum typically settles in blood vessels around the intestines, which is why its symptoms usually include abdominal pain, loss of appetite, diarrhea (with or without blood), and constipation; in more severe cases, it can spread to the nervous system and cause symptoms like convulsions, speech disturbances, and blurring of vision. A subset of patients can develop symptoms a week to a month after getting the parasite. These individuals can experience flu-like symptoms that include fever, headache, fatigue, muscle pain, coughing, diarrhea, and abdominal pain.

Schistosomiasis is suspected in patients who have a history of contact with freshwater in endemic areas and are exhibiting the symptoms mentioned above. To confirm a diagnosis of schistosomiasis, a stool or blood sample is studied under a microscope to look for schistosome eggs; a blood sample can also be tested to look for antibodies against the parasite. If diagnosed and managed early, the disease is curable. However, in advanced stages, it can cause permanent liver and/or kidney damage and can be fatal. Praziquantel tablets, which are available for free in health centers in endemic areas, are used to treat the disease. Stool samples can be taken and examined one to two months after treatment to ensure that the parasite has been completely eradicated.

If a person lives in or is traveling to an area where the disease is common, the best way to prevent infection is to avoid contact with freshwater that is likely contaminated. One should take the following precautions:
• Avoid swimming or wading in fresh water;
• Drink only from a safe water source; if unsure, boil drinking water for at least one minute;
• Take a bath using only safe water; and
• Practice proper personal sanitation measures, especially when defecating. In areas where schistosomiasis cases are high, annual mass drug administration against the parasite can also be done to eradicate the parasite at a community level.