Experimental cryptosporidiosis in laboratory mice

Moist heat inactivation of Cryptosporidium sp

Cryptosporidia that were infective for infant mice were subjected to various moist heat treatments and subsequently tested in infant mice for infectivity. Warming from 9 degrees C to 55 degrees C over a period of 15 to 20 minutes neutralized infectivity in calf feces, cecal contents, and ileal scrapings. Inocula held at 45 degrees C for 5 to 20 minutes lost its infectivity. These results suggest that pasteurization of raw milk, circumstantially incriminated in cryptosporidial transmission, would neutralize cryptosporidial infectivity.

Cryptosporidium infections in man, animals, birds and fish

The protozoan parasite Cryptosporidium has gained better recognition over the last decade as an enteropathogen in a wide variety of host animals. Prior to 1975, infections were thought to occur infrequently and to be largely asymptomatic in nature. However, recent studies have revealed the organism to be more prevalent and pathogenic than previously thought. Infections producing clinical disease have been recorded in numerous host species including man, and the organism is now regarded as a newly-emergent zoonosis. This paper collates information currently available on the host range and specificity, life cycle and pathogenicity of the parasite and summarises the various techniques used to diagnose infections.

Infectivity of a strain of Cryptosporidium found in the guinea-pig (Cavia porcellus) for guinea-pigs, mice and lambs

Cryptosporidiosis was diagnosed in guinea-pigs bred by a commercial laboratory supplier on histological examination of the intestine. Oral transmission to laboratory guinea-pigs aged up to 16 weeks and to infant mice, with gut contents containing oocysts, was successful, but the organism failed to infect adult mice. From day 5 post-inoculation (pi) in guinea-pigs, infection of the ileum was associated with villous stunting and fusion, and with infiltrates of macrophages and other mononuclear cells, and eosinophils. Some guinea-pigs died; others were depressed and anorectic, with diarrhoea or watery caecal contents. Mouse infections were subclinical and caused no significant pathological changes. By contrast, a bovine Cryptosporidium isolate infected infant mice but failed to infect young guinea-pigs. Guinea-pigs and infant mice excreted oocysts in faeces after a prepatent period of 3 to 4 days. Some guinea-pigs excreted oocysts for up to 2 weeks, but excretion in mice lasted only about 4 days. Infection of guinea-pigs by contact with a contaminated environment occurred, with excretion of oocysts between 17 and 27 days after exposure. An indirect fluorescent antibody test (IFA) showed that antibody was present by day 17 pi with infected bowel contents, but none was detected in the guinea-pigs exposed to the contaminated environment. The IFA test demonstrated a serological relationship between the guinea-pig isolate and a bovine strain used to infect gnotobiotic lambs. Transmission electron microscopy of intestine from infected guinea-pigs and mice showed that more than one schizont generation occurred. The first consisted of 8 merozoite packets attached to enterocytes, but many packets of 2 or 4 merozoites of the second or subsequent generations were apparently released into the gut lumen. Fixed microgametocytes contained lipid vacuoles and had microneme-like structures in their cytoplasm. Oocysts and sporocysts were also identified, with sporulation occurring within the parasitiphorous vacuole. A sparse infection was established in 1 of 2 12-day-old specific pathogen-free lambs by day 3 pi, but no oocysts were detected in its caecal contents or those of a second lamb killed 4 days later.

Persistent Cryptosporidium infection in congenitally athymic (nude) mice

Nude (nu/nu) BALB/c mice and their white (nu/+) littermates were experimentally infected with Cryptosporidium sp. at 6 days of age. In white mice, the infection was transient, but in nude mice a persistent infection developed that was characterized by diarrhea and, occasionally, death. There were villus atrophy and crypt hyperplasia in the small intestine of infected nude and white mice necropsied at 11 days of age. Persistently infected nude mice had, in addition to the above small intestinal lesions, diffuse cystic mucosal hyperplasia and crypt abscesses in the large intestine at 56 days of age. These results suggest that T cells are required for recovery from the Cryptosporidium infection but are not required for epithelial cell loss in cryptosporidiosis. Both nude and white mice appeared to be relatively more resistant to Cryptosporidium infection at 42 days of age than at 6 days of age.

Cryptosporidiosis in animals and humans

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