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Schistosomiasis - Overview
Last reviewed: 04.07.2025
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Schistosomiasis, or bilharziasis (Latin: schistosomosis; English: schistosomiasis, bilharziasi), is a tropical helminthiasis characterized in the acute stage by toxic-allergic reactions, and in the chronic stage by predominant damage to the intestines or genitourinary system, depending on the type of pathogen.
The disease schistosomiasis has the following nosological forms: urogenital schistosomiasis, intestinal schistosomiasis, Japanese schistosomiasis and schistosomiasis with predominant intestinal lesions caused by S. intercalatum and S. mekongi.
ICD-10 codes
- B65. Schistosomiasis (bilharziasis).
- B65.0. Schistosomiasis due to Schistosoma haematobium (urogenital schistosomiasis).
- B65.1. Schistosomiasis caused by Schistosoma mansoni (intestinal schistosomiasis).
- B65.2. Schistosomiasis caused by Schistosoma japonicum.
- B65.3. Cercarial dermatitis.
- B65.8. Other schistosomiasis.
- B65.9. Schistosomiasis, unspecified.
Epidemiology of schistosomiasis
The main source of environmental contamination in all schistosomiasis is a sick person. Some animals (monkeys, rodents) can also become infected with S. mansoni, but do not play a significant role in the spread of schistosomiasis. S. japonicum has a much wider range of hosts and, apparently, can affect all mammals and reach sexual maturity in them, so animals, especially domestic ones (cattle, pigs, horses, dogs, cats, etc.), can be a reservoir of infection.
Intermediate hosts of schistosomes are freshwater mollusks: for S. haematobium - the genera Bulinus, Physopsis, Planorbis; for S. mansoni - the genus Biomphalaria; for S. japonicum - the genus Oncomelania. Every day, the body of an infected mollusk is left by up to 1500-4000 or more cercariae, and ultimately, over the life of the mollusk - up to several hundred thousand invasive schistosome larvae.
The natural susceptibility of humans to infection by all five species of schistosomes is universal. In highly endemic foci, human schistosomiasis incidence peaks in the second decade of life, then declines due to developing immunity. A certain level of immunity to superinvasion and low intensity of invasion after reinfection are noted. Schistosomes are most sensitive to the effects of the host's immune mechanisms during the first days after infection, i.e., in the stage of migrating larvae.
A person becomes infected with schistosomiasis while swimming, washing clothes, working in bodies of water, doing agricultural work on irrigated lands, during religious ceremonies and other contacts with contaminated water. Both natural and artificial bodies of water serve as places of infection. The emergence of new foci is facilitated by the construction of new irrigation structures, increased population migration associated with the economic development of new territories, tourism, and pilgrimage. Of the various groups of the population, rural residents, fishermen, gardeners, agricultural workers are most often infected by their type of activity, but the risk of infection of children is especially high (usually children and adolescents aged 7-14 years are infected), since their games are often associated with water. The area of various forms of schistosomiasis covers 74 countries and territories of the world in the tropical and subtropical belt, in which, according to WHO, the number of infected people exceeds 200 million people, of which more than 120 million suffer from clinically manifest forms of the disease, and 20 million have serious complications. In African countries, isolated foci of urogenital and intestinal schistosomiasis, as well as their combined distribution, are noted. In a number of countries in central West Africa (Gabon, Zaire, Cameroon, Chad), foci have been identified where urogenital, intestinal, and intercalate schistosomiasis are registered simultaneously. Isolated foci of urogenital schistosomiasis are noted in the countries of the Near and Middle East, and a combination of urogenital and intestinal schistosomiasis is found in Yemen and Saudi Arabia. The range of Japanese schistosomiasis covers China, Malaysia, the Philippines, Indonesia, and Japan; the range of Mekong schistosomiasis is Kampuchea, Laos, and Thailand. Intestinal schistosomiasis (S. mansoni) is common in the countries of Central and South America and on the islands of the Caribbean (except Cuba).
[ What causes schistosomiasis?
Schistosomes belong to the phylum Plathelminthes, class Trematoda, family Schistosomatidae. Five species of schistosomes: Schistosoma mansoni, Schistosoma haematobium, Schistosoma japonicum, Schistosoma intercalation and Schistosoma mekongi - are the causative agents of helminthiasis in humans. Schistosomes differ from all other representatives of the class Trematoda in that they are dioecious and have sexual dimorphism. The body of sexually mature schistosomes is elongated, cylindrical, covered with a cuticle. There are suckers located close to each other - oral and abdominal. The body of the female is longer and thinner than that of the male. Along the body of the male there is a special copulatory groove (gynecoform canal), in which the male holds the female. The male and female are almost always together. The outer surface of the male is covered with spines or tubercles, while the female has spines only on the front end of the body, the rest of the surface is smooth.
What are the symptoms of schistosomiasis?
Urogenital schistosomiasis is caused by Schistosoma haematobium. The male is 12-14 x 1 mm, the female is 18-20 x 0.25 mm. The eggs are elongated, oval, with a spine at one pole. The size of the eggs is 120-160 x 40-60 µm. The female lays eggs in small vessels of the bladder and genitals.
Urogenital schistosomiasis has three stages: acute, chronic and outcome stage.
Symptoms of schistosomiasis associated with the introduction of cercariae in the form of allergic dermatitis in non-immune individuals are rarely recorded. After 3-12 weeks of the latent period, acute schistosomiasis may develop. Typical symptoms of schistosomiasis appear: headaches, weakness, widespread pain in the back and limbs, loss of appetite, increased body temperature, especially in the evening, often with chills and heavy sweating, urticarial rash (inconstant); hypereosinophilia is characteristic (up to 50% and higher). The liver and spleen are often enlarged. Disorders of the cardiovascular system and respiratory organs are revealed.
How is schistosomiasis diagnosed?
Schistosomiasis in the acute period is diagnosed taking into account the epidemiological history and the presence of signs of “cercarial dermatitis” after swimming in contaminated bodies of water.
Urine is examined after centrifugation, keeping in mind that the maximum number of eggs is excreted with urine between 10 a.m. and 2 p.m. Invasion is assessed as intensive when the number of S. haematobium eggs is more than 50 in 10 ml of urine and more than 100 S. mansoni, S. japonicum, S. intercalatum and S. mekongi eggs in 1 g of feces. Schistosome eggs in feces are detected using various methods of coproovoscopy: examination of a native smear (ineffective), sedimentation after dilution of feces, preparation of smears according to Kato-Katz, etc. The tests must be repeated many times, especially in cases of chronic course and development of fibrous changes in the intestine.
How to examine?
What tests are needed?
How is schistosomiasis treated?
Antiparasitic treatment of schistosomiasis is carried out in a hospital setting. Semi-bed rest, no special diet is required. In case of liver damage - table No. 5.
Schistosomiasis is currently treated with praziquantel, a highly effective drug for all forms of helminthiasis. The drug is prescribed at a dose of 40-75 mg/kg in 2-3 doses after meals at intervals of 4-6 hours for 1 day. Side effects are recorded quite often, but they are mild and short-lived: drowsiness, dizziness, headache, weakness, abdominal pain, sometimes skin rashes.
How to prevent schistosomiasis?
Schistosomiasis can be prevented by implementing a set of measures aimed at stopping the transmission of the invasion and preventing infection of people. It is possible to destroy schistosomes or stop them from releasing eggs by timely detection and specific treatment of patients. Mollusks and cercariae are destroyed in water bodies using chemical and biological agents. Infection of people in infected water can be prevented by using protective clothing (gloves, rubber boots, etc.) or repellents. Currently, mass chemotherapy and the use of molluscicides are of the greatest importance in programs to combat schistosomiasis. At all stages of the fight against schistosomiasis, great importance is attached to active sanitary and educational work among the population of endemic foci, especially among schoolchildren.