Schistosomiasis

Schistosomiasis, also known as snail fever, bilharzia, and Katayama fever is a neglected tropical disease caused by parasitic flatworms called schistosomes. It affects both humans and animals. It affects the urinary tract or the intestines. Symptoms include abdominal pain, diarrhea, bloody stool, or blood in the urine. Those who have been infected for a long time may experience liver damage, kidney failure, infertility, or bladder cancer. In children, schistosomiasis may cause poor growth and learning difficulties. Schistosomiasis belongs to the group of helminth infections.

Schistosomiasis is spread by contact with fresh water contaminated with parasites released from infected freshwater snails. Diagnosis is made by finding the parasite's eggs in a person's urine or stool. It can also be confirmed by finding antibodies against the disease in the blood.

Methods of preventing the disease include improving access to clean water and reducing the number of snails. In areas where the disease is common, the medication praziquantel may be given once a year to the entire group. This is done to decrease the number of people infected, and consequently, the spread of the disease. Praziquantel is also the treatment recommended by the World Health Organization (WHO) for those who are known to be infected.

The disease is especially common among children in underdeveloped and developing countries because they are more likely to play in contaminated water. Schistosomiasis is also common among women, who may have greater exposure through daily chores that involve water, such as washing clothes and fetching water. Other high-risk groups include farmers, fishermen, and people using unclean water during daily living. In 2019, schistosomiasis impacted approximately 236.6 million individuals across the globe. Each year, it is estimated that between 4,400 and 200,000 individuals succumb to it. The illness predominantly occurs in regions of Africa, Asia, and South America. Approximately 700 million individuals across over 70 nations reside in regions where the disease is prevalent. In tropical regions, schistosomiasis ranks as the second most economically significant parasitic disease, following malaria. Schistosomiasis is classified as a neglected tropical disease.

Many individuals do not experience symptoms. If symptoms do appear, they usually have an incubation period of about 4–6 weeks. The first symptom of the disease may be a general feeling of illness. Within 12 hours of infection, an individual may develop cercarial dermatitis due to irritation at the point of entrance, commonly referred to as "swimmer's itch". The rash that may develop can mimic scabies and other rashes.

The manifestation of a schistosomal infection varies over time as cercariae, (the larval form of the parasite) and later the adult worms and their eggs, migrate through the body. If eggs migrate to the brain or spinal cord, seizures, paralysis, or spinal cord inflammation are possible.

Manifestation of acute infection from schistosomiasis includes cercarial dermatitis (hours to days) and acute systemic schistosomiasis (2–8 weeks) which can include symptoms of fever, myalgia, a cough, bloody diarrhea, chills, or lymph node enlargement. Some patients may also experience dyspnea and hypoxia associated with the development of pulmonary infiltrates.

The first potential reaction is an itchy, maculopapular rash that, within the first 12 hours to days of penetration, results from cercariae penetrating the skin. The first time a non-sensitized person is exposed, the rashes are usually mild with an associated prickling sensation that quickly disappears on its own since this is a type of hypersensitivity reaction.^{[clarification needed]} In sensitized people who have previously been infected, the rash can develop into itchy, red, raised lesions (papules) with some turning into fluid-filled lesions (vesicles). Previous infections with cercariae causes a faster developing and worse presentation of dermatitis due to the stronger immune response. The round bumps are usually one to three centimeters across. Because people living in affected areas have often been repeatedly exposed, acute reactions are more common in tourists and migrants. The rash can occur between the first few hours and a week after exposure, and they normally resolve on their own in around 7–10 days. For human schistosomiasis, a similar type of dermatitis called "swimmer's itch" can also be caused by cercariae from animal trematodes that often infect birds. Cercarial dermatitis is not contagious and can not be transmitted from person-to-person.