Life cycle of the large type of Isospora bigemina of the cat
Ito, S.; Tsunoda, K.; Shimura, K.
National Institute of Animal Health Quarterly 18(2): 69-82
1978
ISSN/ISBN: 0027-951X PMID: 357997 Document Number: 136376
Large-type oocysts of Isospora bigemina from the faeces of cats in Japan were given orally to kittens but no infections became established. Kittens did become infected, however, when fed organs of mice which, 30 or more days previously, had been inoculated orally with oocysts. The cats began to shed unsporulated, large-type oocysts in their faeces after 12 to 15 days and oocyst shedding continued usually for 8 to 20 days (occasionally for as long as 38 days). In mice given oocysts, trophozoite-like organisms were found in the mesenteric lymph nodes after 2 to 11 days but these were not infective to cats. After 25 days young cysts were found in the wall of the gut and, later, in various other organs. Rats and Mongolian gerbils were more susceptible to infection than mice. Rats contained young cysts in the brain, lungs, mesenteric lymph nodes and intestine 17 days after infection and, after 27 days, mature Besnoitia-like cysts were present. Most were 150 to 250 mu m in diameter and they were PAS positive. Cysts present after 24 days or more (but not 21 days) were infective to cats. Rabbits and voles, but not hamsters, also harboured cysts after receiving oocysts. In cats fed cysts, young schizonts were found in the lamina propria of the jejunum after 6 to 8 days, and giant schizonts were seen in the same site after 8 to 10 days. Giant schizonts were PAS-positive. After 12 days the intestine contained free merozoites, giant and mature schizonts, gametocytes, gametes, zygotes and unsporulated oocysts. Dogs could not be infected with cysts, and rodent-to-rodent transmission failed.