Within 12 hours of infection, an individual may complain of a tingling sensation or light rash, commonly referred to as "swimmer's itch due to irritation at the point of entrance.

The manifestation of a schistosomal infection varies over time as the larval form of the parasite cercariae and later adult worms and their eggs migrate through the body.

[19] The first time a non-sensitized person is exposed, the rashes are usually mild with an associated prickling sensation that quickly disappear on its own since this is a type of hypersensitivity reaction.

[19] Previous infections with cercariae causes a faster developing and worse presentation of dermatitis due to the stronger immune response.

[21][19] 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.

[19] Symptoms may include: Acute schistosomiasis usually self-resolves in 2–8 weeks in most cases,[25] but a small proportion of people have persistent weight loss, diarrhea, diffuse abdominal pain, and rash.

The enzymes also cause an eosinophilic inflammatory reaction when eggs get trapped in tissues or embolize to the liver, spleen, lungs, or brain.

[23] Eggs can become lodged in the liver,[31] leading to portal hypertension, splenomegaly, the buildup of fluid in the abdomen, and potentially life-threatening dilations or swollen areas in the esophagus or gastrointestinal tract that can tear and bleed profusely (esophageal varices).

In situ egg deposition following the anomalous migration of the adult worm, which appears to be the only mechanism by which Schistosoma can reach the central nervous system in people with schistosomiasis.

[36] The destructive action on the nervous tissue and the mass effect produced by a large number of eggs surrounded by multiple, large granulomas in circumscribed areas of the brain characterize the pseudotumoral form of neuroschistosomiasis and are responsible for the appearance of clinical manifestations: headache, hemiparesis, altered mental status, vertigo, visual abnormalities, seizures, and ataxia.

[45] The infectious stage starts when the free-swimming larval form of the schistosome, cercariae, penetrates the human skin using their suckers, proteolytic enzymes, and tail movements; the cercariae transformed into schistosomulae by losing its tail and subsequently travels to the heart and lungs through the venous system until it eventually reaches the liver where it will mature into the adult form.

[49] Antibody detection can be useful to indicate schistosome infection in people who have traveled to areas where schistosomiasis is common and in whom eggs cannot be demonstrated in fecal or urine specimens.

[48] At the U.S. Centers for Disease Control and Prevention, a combination of tests with purified adult worm antigens is used for antibody detection.

The antibody's presence only indicates that schistosome infection occurred at some time and cannot be correlated with clinical status, worm burden, egg production, or prognosis.

[53] This is due to the high level of inflammation caused by the schistosomal eggs, which increases the metabolic rate of the surrounding tissues.

In some cases, urbanization, pollution, and the consequent destruction of snail habitat have reduced exposure, with a subsequent decrease in new infections.

[54] The Centers for Disease Control and Prevention advises avoiding drinking or coming into contact with contaminated water in areas where schistosomiasis is common.

[55] A 2014 review found tentative evidence that increasing access to clean water and sanitation reduces schistosome infection.

[56] Other important preventive measures include hygiene education leading to behavioral change and sanitary engineering to ensure a safe water supply.

[12] For many years from the 1950s onwards, vast dams and irrigation schemes were constructed, causing a massive rise in water-borne infections from schistosomiasis.

Irrigation schemes can be designed to make it hard for the snails to colonize the water and to reduce contact with the local population.

After the construction of fourteen large dams, greater increases in schistosomiasis occurred in the historical habitats of native prawns than in other areas.

The morbidity control strategy focused on synchronous chemotherapy for humans and bovines and the new strategy developed in 2004 intervenes in the transmission pathway of schistosomiasis, mainly including replacement of bovines with machines, prohibition of grazing cattle in the grasslands, improving sanitation, installation of fecal-matter containers on boats, praziquantel drug therapy, snail control, and health education.

[70] The disease is found in tropical countries in Africa, the Caribbean, eastern South America, Southeast Asia, and the Middle East.

[citation needed] The disease is endemic in about 75 developing countries and mainly affects people living in rural agricultural and peri-urban areas.

[72][76] S. haematobium, the infectious agent responsible for urogenital schistosomiasis, infects over 112 million people annually in Sub-Saharan Africa alone.

Even though this evidence comes from the Middle East, it has been suggested that the 'cradle' of schistosomes lies in the region of the African Great Lakes, an area in which both the parasites and their intermediate hosts are in an active state of evolution.

Subsequently, it is believed that schistosomiasis spread to Egypt as a result of the importation of monkeys and slaves during the reign of the fifth dynasty of the Pharaohs (ca.

[89] By the early 20th century, schistosomiasis' symptom of blood in the urine was seen as a male version of menstruation in Egypt and was thus viewed as a rite of passage for boys.

[90][91] Among human parasitic diseases, schistosomiasis ranks second behind malaria in socio-economic and public health importance in tropical and subtropical areas.