The elicci of mouse strain, age, sex, and the size of infective dose on the susceptibility to infection with the coccidium Cryptosporidium, parvum Tyzzer, 1912 was determined using several murine models. Mice were infected with C. parvum oocysts originally of cervine origin, maintained by repeat passage in calves. All mice in the experimental groups proved susceptible to infection, though this resulted asymptomatic in all cases. C. parvum infection in BALB/c and Porton mice exhibited some variation. BALB/c mice demonstrated a longer prepatent period than Porton mice. They also produced a greater oocyst output over the patent period, though the differences were not statistically significant. Differences were observed between mice infected at either 3 or 4 weeks of age. Prepatent period was shorter in those mice infected at 3 weeks of age, reaching 100% infection rate by day 7 post-inoculation. The patent period was longer in younger mice showing that age at time of infection can modify the oocyst shedding profile. However, no sex related differences in the course of infection were observed. The effect of different infective doses of oocysts was analysed. The three doses used (l-O4, IO5, 106) proved infective for all mice, there were no statistical differences in either prépaient or patent periods, or in the oocyst shedding profiles. Experimental cryptosporidiosis was also induced in cyclophosphamide-immunosuppressed mice. Cyclophosphamide was orally administered by stomach lube at a dose of 50 mg/kg/day starting 10 days before the intragastric inoculation of 10fi oocysts of C. parvum per mouse and continuing until the end of the experiment, Immunosupprcsscd mice had a shorter prepatent period, remained infected longer and shed more oocysts than immunocompetent mice. Immunosuppression produced high mortality rates; during the course of the experiment 44% of immunosuppressed-infcctcd and 30% of immunosuppressed-uninfccted mice died. There were no deaths in the untreated groups. Differences in the clinical course of the infection were also observed between immunosuppressed and immunocompetent mice; however, some mice recovered without immunosuppression withdrawal.
We report the findings of a longitudinal observational study on HIV-infected patients grouped by presumed transmission group, who had diarrhoea. The purpose of this study was to assess the prevalence of and factors associated with Cryptosporidium infection on these patients. Modified formol-ether concentration followed by modified Ziehl-Neelsen and phenol-auraminc/carbol-fuchsin staining techniques were used to identify Cryptosporidium from 465 patients. Cryptosporidiosis was reported in 36/465 (8% and 95% confidence interval 6, 10) patients. Of the positive patients 30 (83%) were men and 6 (17%) women. Prevalence of infection was higher among HIV-seropositive patients whose exposure category was through sexual contact (69%) than among patients in other HIV exposure categories (9%, Standard Z test, P < 0.001). Median CD4+ cell count/mm3 was 120 (range 3-600). Besides diarrhoea, the main clinical manifestations were fever and weight loss in 14 (39%) and 26 (72%) patients, respectively. Cryptosporidium infection was considered to be the first AIDS defining disease in 31% of the patients followed by tuberculosis in 19%, Pneumocystis carinii pneumonia in 14%, Salmonella sepsis in 6%, isosporiasis in 3%, toxoplasmic encephalitis in 3%, leishmaniasis in 3% and Kaposi’s sarcoma in 3% of the patients. There was no significant difference (P = 0.82) in survival times for those given folate antagonists to treat other opportunistic infections. The decrease in prevalence of cryptosporidiosis observed from 1994 until May 1997 is not statistically significant (P = 0.11). Most cases of cryptosporidial infection in AIDS patients in Lisbon occurred in those whose HIV infection was assumed to have been acquired by the sexual route (hetero-, homo- and bisexual), with few cases occurring in drug-abusers.