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Schistosomiasis: an overview
Last reviewed: 23.04.2024
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Schistosomiasis, or bilharziasis (Latin schistosomosis, English schistosomiasis, bilharziasi), is a tropical helminthiasis characterized by acute toxic allergic reactions in the acute stage, in the chronic one - a primary lesion of the intestine or genitourinary system, depending on the type of pathogen.
The disease of schistosomiasis has the following nosological forms: urogenital schistosomiasis, intestinal schistosomiasis, Japanese schistosomiasis and schistosomiasis, caused by the predominant intestinal lesion, caused by S. Intercalatum and S. Mekongi.
ICD-10 codes
- Q65. Schistosomiasis (bilharziosis).
- B65.0. Schistosomiasis caused by Schistosoma haematobium (urogenital schistosomiasis).
- B65.1. Schistosomiasis. Caused by Schistosoma mansoni (intestinal schistosomiasis).
- B65.2. Schistosomiasis. Caused by Schistosomajaponicum.
- B65.3. Cercarium 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 they do not play an important 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, therefore animals, especially domestic animals (cattle, pigs, horses, dogs, cats, etc.) may be reservoir infection.
Intermediate hosts of schistosomes are freshwater mollusks: for S. Haematobium - genera Bulinus, Physopsis, Planorbis: for S. Mansoni - genus Biomphalaria; for S. Japonicum - the genus Oncomelania. Every day the body of an infected mollusc leaves up to 1500-4000 or more cercariae, and as a result, during the life of the mollusk - up to several hundred thousand invasive larvae of schistosomes.
The natural susceptibility of people to infection with all five kinds of schistosomes is universal. In highly endemic foci, the incidence of schistosomiasis peaks in the second decade of life, then decreases as a result of emerging immunity. They note a certain level of immunity to superinvasia and low intensity of invasion after reinfection. Schistosomes are most sensitive to the immune mechanisms of the host organism during the first days after infection, i.e. In the stage of migrating larvae.
A person becomes infected with schistosomiasis during bathing, washing clothes, working in reservoirs, agricultural work on irrigated lands, during religious rites and other contacts with contaminated water. The place of infection is both natural and artificial reservoirs. The appearance of new foci is facilitated by the construction of new irrigation facilities, increased migration of the population, associated with the economic development of new territories, tourism, pilgrimage. Of the various groups of the population, rural residents, fishermen, horticulturists, and agricultural workers are more likely to become infected, 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 range of various forms of schistosomiasis covers 74 countries and territories in the world of 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 clinically manifested forms of the disease, and 20 million have serious complications. In African countries, isolated foci of urogenital, intestinal schistosomiasis and their associated distribution are noted. A number of countries in the center of West Africa (Gabon, Zaire, Cameroon, Chad) have identified foci where both urino-genital, intestinal and intercalatonal schistosomiasis are recorded. Isolated foci of genitourinary schistosomiasis are noted in the countries of the Near and Middle East, and a combination of urinary and intestinal schistosomiasis in Yemen, Saudi Arabia. The area of Japanese schistosomiasis includes China, Malaysia, the Philippines, Indonesia, Japan; the area of mekong bishoplasmosis is Kampuchea, Laos. Thailand. In countries of Central and South America and the islands of the Caribbean (with the exception of Cuba), intestinal schistosomiasis (S. Mansoni) is widespread .
[What causes schistosomiasis?
Schistosomes are of the type Plathelminthes, class Trematoda, family Schistosomatidae. Five species of schistosomes: Schistosoma mansoni, Schistosoma haematobium, Schistosoma japonicum, Schistosoma intercalation and Schistosoma mekongi - causative agents of helminthiosis in man. Schistosomes differ from all other representatives of the Trematoda class. That they are dioecious and differ in sexual dimorphism. The body of mature sexually schistosomes is elongated, cylindrical, covered with 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 (gyneco-form canal) in which the male retains the female. The male and female are almost always together. The external surface of the male is covered with spines or tubercles, the female spines are present only at the anterior end of the body, the rest of the surface is smooth.
What are the symptoms of schistosomiasis?
Genitourinary schistosomiasis is caused by Schistosoma haematobium. The male has dimensions of 12-14 x 1 mm, the female - 18-20 x 0.25 mm. Eggs elongated, oval, with a spine on one pole. The size of eggs is 120-160 x 40-60 microns. The female lays eggs in small vessels of the bladder and genital organs.
Genitourinary schistosomiasis has three stages: acute, chronic and stage of outcome.
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 a latent period, acute schistosomiasis may develop. There are typical symptoms of schistosomiasis: headaches, weakness, common soreness in the back and extremities, lack of appetite, body temperature rises, especially in the evening, often with chills and strong sweat, observe urticaria rash (unstable); characterized by hypereosinophilia (up to 50% and higher). The liver and spleen are often enlarged. Identify violations of the cardiovascular system and respiratory system.
How is schistosomiasis diagnosed?
Schistosomiasis in the acute period is diagnosed, taking into account the epidemiological anamnesis, the presence of signs of "cervical dermatitis" after bathing in the infected reservoirs.
Urine test is performed after centrifugation, and it should be borne in mind that the maximum number of eggs is excreted in the urine between 10 and 14 hours of the day. The invasion is assessed as intensive with the number of eggs of S. Haematobium more than 50 in 10 ml of urine and more than 100 eggs of S. Mansoni, S. Japonicum, S. Intercalatum and S. Mekongi in 1 g of feces. Eggs of schistosomes in faeces are detected with the help of various methods of coprocopy: research of the native smear (ineffective), precipitation after breeding of feces, preparation of smears by Kato-Katz, etc. Analyzes 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 performed in a hospital. Semi-bed, special diet is not required. With liver damage - table number 5.
Schistosomiasis is currently treated with a prazikvantel - a highly effective drug for all forms of helminthiosis. The drug is prescribed in a dose of 40-75 mg / kg in 2-3 meals after meals with an interval of 4-6 hours for 1 day. Adverse reactions are recorded quite often, but they are mild and short-lived: drowsiness, dizziness, headache, weakness, abdominal pain, sometimes rashes on the skin.
How to prevent schistosomiasis?
Schistosomiasis can be prevented by carrying out a set of measures designed to stop the transmission of infestation, to prevent the infection of people. Destroy shistosoma or stop the allocation of eggs can be due to timely detection and specific treatment of patients. With the help of chemical and biological agents in water bodies, mollusks and cercariae are destroyed. To prevent contamination of people in infected water, you can use protective clothing (gloves, rubber boots, etc.) or repellents. At present, 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.