Schistosomes

Mammals act as the final host. Free-floating larvae ( cercariae ) infect by penetrating the skin, mucous membranes or by ingestion.

They inhabit and mate in venous blood . In the body of mammals, they also feed on blood.

The human body is mainly penetrated by bathing in a pond through the skin, mucous membranes or ingestion.

During sexual development, a significantly smaller female settles in a fold on the ventral side of the male. Further, such a pair continuously produces from 300 to 3000 eggs per day.

The life cycle of all types of schistosomes follows a common path of development.

When feces or urine infected with schistosome eggs fall into fresh water, miracidia hatch from the eggs, they quickly swim with the help of cilia , which cover the surface of their body. Further, miracidia penetrate the body of the cochlea, their intermediate host. Types of snails that serve as an intermediate host may differ for each species of schistosome ^[1] .

After penetrating the intermediate host, miracidia loses the ciliary surface and develops into the maternal sporocyst and daughter sporocyst , and then produces cercaria within a few weeks. As a result of the asexual reproduction of the mother and daughter sporocysts, thousands of cercariae, all of the same sex, appear. Cercariae reaches a size of about 400 μm in length, including the tail, the final third of which is bifurcated. Cercariae infect the final host by penetrating the skin, thanks to the enzymes that they secrete from the penetrating glands. Penetrating into the skin, they lose their tails and turn into the next larval stage - schistosome. Then, schistosomes migrate to the lungs through venous circulation. From the lungs, they penetrate into the systemic circulation through the left heart, finally reaching the portal blood supply system. After a few weeks, the schistosomes reach puberty, they form pairs and migrate to the mesenteric veins, where the females lay their eggs ^[2] .

For S. mansoni and S. japonicum, the period between the penetration of cercaria and the first appearance of eggs in excrement is about 35 days.

Once the eggs have been released by the female inside the vasculature, they cross the endothelium and the basement membrane of the vein, cross the intermediate tissue, basement membrane and intestinal epithelium (S. mansoni and S. japonicum) or the bladder (S. haematobium) to exit the eggs with feces or urine ^[2] .

The most dangerous are the spikes on the eggs of schistosomes, which, piercing and damaging, pass through the walls of blood and lymph vessels into different organs and tissues: the bladder, uterus, prostate, liver, spleen, lungs, heart, stomach, intestines.

In places where parasites and eggs accumulate, the lumen in the vessels and ducts is blocked, which leads to varicose veins, cysts and tumors. They can cause fibrosis in the liver, cancer of the bladder , prostate, liver.

Schistosomatosis can cause a number of severe damage to organs, in particular the bladder, and can also cause hematuria or malfunction of the large intestine .

As a preventive measure, it is recommended to wash hands before eating, wash vegetables and completely prohibit swimming in tropical ponds.

The treatment is conservative (with trivalent antimony and thioxantonic compounds). The course of treatment is 12 intravenous injections of a 1% solution of antimonil - sodium tartrate every other day for 4 weeks. The initial dose of 3 ml is gradually increased to 13 ml. The course dose is 150 ml (1.5 g).

Ambilgar is taken orally at the rate of 24 mg / kg 24 hours for 5-7 days.

Etrenol - once.

Surgical treatment - for complications (stenosis of the ureter). The prognosis is favorable with timely specific therapy.

• A person is infected mainly with three types of schistosomes - Schistosoma mansoni, Schistosoma haematobium and Schistosoma japonicum and some less common representatives of the genus Schistosoma.

Schistosoma bovis

• Schistosoma curassoni
• Schistosoma edwardiense
• Schistosoma guineensis
• Schistosoma incognitum
• Schistosoma indicum
• Schistosoma intercalatum
• Schistosoma japonicum - Japanese schistosome . Parasitizes in the veins of the large intestine and abdominal cavity.
• Schistosoma haematobium - Blood schistosome . Parasitizes in the blood vessels of the bladder.
• Schistosoma hippotami
• Schistosoma leiperi
• Schistosoma malayensis
• Schistosoma mansoni - Schistosoma Manson . Parasitizes in the veins of the large intestine and abdominal cavity.
• Schistosoma margrebowiei
• Schistosoma matthei
• Schistosoma mekongi
• Schistosoma nasale
• Schistosoma ovuncatum
• Schistosoma rodhaini
• Schistosoma sinensium
• Schistosoma spindale

In some tropical countries, almost the entire population is infected with schistosomes.

• Zaikina I.V. Urology: textbook. allowance for students of higher medical. textbook. institutions. - M .: VLADOS-PRESS, 2005.

• Beer S.A. , Voronin M.V. Biology of pathogens of schistosomiasis. - M .: The volume of scientific publications of KMK, 2011. - 200 p. - 400 copies. - ISBN 978-5-87317-697-7 .
• Voronin M.V. Schistosomatids - causative agents of cercariosis in urban ecosystems: On the example of Moscow metropolis: abstract of thesis. ... candidate of biological sciences: 03.00.19 / Institute of Parasitology, RAS. - Moscow, 2003 .-- 23 p.
• Topley and Wilson's microbiology and microbial infections. Parasitology / Edited by Francis EG Cox, Derek Wakelin, Stephen H. Gillespie, Dickinson D. Despommier. - Hodder Arnold, 2007. - T. 6. - ISBN 9780340885680 .

• British Department for International Development Control of Schistosomiasis
• The world health organization
• University of Cambridge Schistosome Laboratory
• Schistostoma parasites overview, biology, life cycle image at MetaPathogen