Cryptosporidiosis: Causes and Pathogenesis
Last reviewed: 23.04.2024
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Causes of cryptosporidiosis
The cause of cryptosporidiosis is coccidia of the genus Cryptosporidium, family Cryptosporidiae, class Sporozoasida, subclass Coccidiasina. The genus Cryptosporidium includes 6 species, of which P. Pervum is pathogenic for humans. Cryptosporidia are obligate parasites that infect microvilli of the mucous membranes of the gastrointestinal tract and respiratory tract of animals and humans.
The life cycle of cryptosporidium passes in the body of one host, includes the stages of schizogony, megohonia. Gametogony and sporogony. Localized cryptosporidia in the parasitiform vacuole formed by intestinal microvilli, therefore the parasite is located intracellularly, but extraplasmatically. Merozoites of the first generation are capable of proliferating in two directions: to the schizonts of the first or to the schizonts of the second generation, so the number of parasites increases. In the host organism, two types of oocysts are formed: thick-walled - leaving the host with faeces. And thin-walled - releasing sporozoites in the intestine, resulting in possible autoinfection.
Oocysts of cryptosporidia, remaining in the environment, are capable of infestation for 18 months at a temperature of 4 ° C and 1 week at -10 ° C. When heated to 72 ° C, they die within 1 minute.
Oocysts are resistant to the action of disinfectants, especially those containing chlorine. In this regard, as well as with their small size (4-7 microns). Allowing to pass through many filters, water purification from cryptosporidium with the help of modern technologies is impossible, the poet} - the infection spreads by water.
At present, there is no single sufficiently effective drug to which cryptosporidia would be sensitive.
[Pathogenesis of cryptosporidiosis
The pathogenesis of cryptosporidiosis is not well understood. The predominance of cholera-like profuse watery diarrhea in the clinical picture of the disease suggests the production of enterotoxin, but despite numerous searches, the toxin in cryptosporidia has not been detected. Some studies have shown the presence of a gene responsible for the production of a protein with hemolytic activity similar to that of E. Coli 0157 H7 in cryptosporidia . The most typical localization of the process is the distal parts of the small intestine. After the oocyst enters the intestine, the increased multiplication of the parasite begins; the resulting merozoites spread and affect a large number of enterocytes, causing degenerative changes in them (atrophy of the villi). This is accompanied by hypertrophy of crypts, mono- and polymorphonuclear infiltration of the basal membrane and leads to the appearance of craterial depressions on the surface of the epithelium. In severe forms of the disease, total microvilli damage occurs.
As a result of massive damage to microvilli, water and electrolytes are absorbed, their secretion through the intestinal wall increases, which is manifested by watery diarrhea. Violated enzymatic activity of the intestine, there are secondary malabsorption and steatorrhea. In patients with severe immunodeficiency, not only the gastrointestinal tract, but also the hepatobiliary system and respiratory tract can be affected.
The most important factor determining the susceptibility to invasion and the severity of cryptosporidiosis is the state of immunity. The role of humoral immunity is proved, but the main importance is the violation of T-cell function.