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Chapter: Medical Microbiology: An Introduction to Infectious Diseases: Sporozoa

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Cryptosporidiosis

Cryptosporidiosis is an intestinal illness acquired from domestic animals. The course includes profuse watery diarrhea, vomiting, and weight loss. Spontaneous complete recovery is the usual outcome.

CRYPTOSPORIDIOSIS

Cryptosporidiosis is an intestinal illness acquired from domestic animals. The course includes profuse watery diarrhea, vomiting, and weight loss. Spontaneous complete recovery is the usual outcome.

EPIDEMIOLOGY

Cryptosporidiosis appears to involve most vertebrate groups. In all species, infection rates are highest among the young and immature. Experimental and epidemiologic data suggest that domestic animals constitute an important reservoir of disease in humans. However, outbreaks of human disease in day-care centers, hospitals, and urban family groups indi-cate that most human infections result from person-to-person transmission. In Western countries, between 1 and 4% of small children presenting to medical centers with gas-troenteritis have been shown to harbor cryptosporidia oocysts. In third world countries, the rates have varied from 4 to 11%. In some outbreaks of diarrhea in day-care centers, the majority of attendees were found to have oocysts in their stool.

Infection rates in adults suffering from gastroenteritis is approximately one third of that reported in children; it has been highest in family members of infected children, medical personnel caring for patients with cryptosporidiosis, male homosexuals, and trav-elers to foreign countries. In the United States, the parasite has been identified in 15% of patients with AIDS and diarrhea; in Haiti and Africa, 50% of such individuals may be involved. Asymptomatic  carriage  is  uncommon.  Other  enteric  pathogens,  particularly Giardia lamblia, are recovered from a significant minority of infected patients.

Because  oocysts  are  found  almost  exclusively  in  stool,  the  principal  transmission route is undoubtedly by direct fecal–oral spread. Transmission via contaminated water has been documented, and the hardy nature of the oocysts makes it likely that there is also indirect transmission via contaminated food and fomites.

PATHOGENESIS AND IMMUNITY

Although the jejunum is most heavily involved, cryptosporidia have been found throughout the gastrointestinal tract, particularly in immunocompromised subjects. Cryptosporidial cholecystitis is seen with some frequency in AIDS patients with enteritis. By light mi-croscopy, bowel changes appear minimal, consisting of mild to moderate villous atrophy, crypt enlargement, and a mononuclear infiltrate of the lamina propria. The pathophysiology of the diarrhea is unknown, but its nature and intensity suggest that a cholera-like enteroα-Toxin may be involved. The vital role played by the host’s immune status in the pathogene-sis of the disease is indicated by both the enhanced susceptibility of the young to infection and the prolonged severe clinical disease seen in immunocompromised patients. Indirect evidence suggests antibodies in the intestinal lumen exert a protective effect against initial C. parvum infection. Experimental animal studies indicate that CD4 T lymphocytes andinterferon play independent roles in the immunologic clearance of the parasite.

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