Abstract
The prevalence of Cryptosporidium in naturally infected calves,
mice, rats and chicks along with experimental cross-transmission
and limited anti-cryptosporidial drug efficacy studies were
performed. Cryptosporidium oocysts were detected in 45 (8.30%)
of the 545 calves examined. Forty-three (13.73%) of the oocysts
were excreted by 313 calves with diarrhoea while 2 (0.86%) were
excreted by 232 calves without diarrhoea (P<0.01). In the
diarrhoeal calves the infection was found throughout the year,
highest (22.58%) being in the warm-wet months (August-September)
and lowest (5.25%) in the cold-dry months (December-January).
Clinical cryptosporidiosis was not prevalent in the naturally
infected laboratory or wild rodents. Of the 916 faecal samples
examined from laboratory mice (Swiss Albino strain) oocysts were
detected in 24 (2.62%). The infection was evident from March
through October, highest being in July (8.82%). From November to
February no cryptosporidia could be isolated from the faecal
samples of laboratory mice. In wild mice the overall infection
rate was 10.89%. The infection was prevalent all the year round
lowest being in the month of January (3.84%) and highest
being in the month of August (30%). 0f the 923 faecal
samples examined from the laboratory rats (Long Evans
strain) oocysts were detected in 23 (2.49%). The infection
existed from March through October, highest (6.66%) being in
the month of July. From November to February there was no
evidence of infection. In the wild rats the overall
infection rate was 7.69%. The infection was prevalent all
the year round except in the month of January when no
cryptosporidial oocysts were detected. Cryptosporidial oocysts were detected in 49 (6.95%) of the 705
chicks examined. Forty-seven (10.93%) of the oocysts were
excreted by 430 chicks with diarrhoea while 2 (0.72%) were
excreted by 275 chicks without diarrhoea (P<0.01). The
infection was found throughout the year in the chicks with
diarrhoea, highest (28.88%) being in the warm-wet month (August)
and lowest being (3.22%) in the cold-dry month (January).
The pathological lesions in both natural and experimental animals
were mostly confined in the distal part of the small intestine.
The affected villi become shortened or blunted. The lining
epithelium became flat or cuboidal and the lamina propria was
found to be infiltrated with plasma cells, lymphocytes and
sometimes with neutrophils and eosinophils.
Cross-transmission studies indicated that isolate of mammalian
origin produced detectable infection in mammalian hosts only and
not in the avian hosts. Again Cryptosporidium of avian source
produced infection in the avian species and not in the mammalian
hosts suggesting the possibilities of the host-specificity of the
protozoan.
An animal model for persistent cryptosporidiosis was successfullу
established by treating the adult Long Evans strain rats with
cyclophosphamide in drinking water. The drug was used for a
period of two weeks at the rate of 25 mg/kg body weight.
The effects of some chemotherapeutic agents used against
persistent cryptosporidiosis in rats were also assessed.