Infectivity of a Cryptosporidium species isolated from a domestic cat (Felis domestica) in lambs and mice.

Two neonatal lambs were inoculated orally with purified Cryptosporidium species oocysts isolated from a farm cat. Oocysts first appeared in the faeces of the two lambs three and 10 days after infection. Two distinct sizes of oocysts were observed in the faeces of both the cat and the lambs, the smaller measuring approximately 5.0 x 4.5 microns and the larger measuring approximately 6.0 x 5.0 microns in diameter. The smaller type predominated. Histological examination of the alimentary tract of the lambs revealed endogenous stages of Cryptosporidium in the epithelial borders of the ileum. In addition, Cryptosporidium oocysts were detected in impression smears from the jejunum, ileum, caecum and colon. Suspensions of 10(3) oocysts from the faeces of the farm cat were inoculated into each of 10 newborn mice and 10(4) oocysts from the two experimentally infected lambs were inoculated into each of 20 newborn mice. Cryptosporidium oocysts were detected in gut homogenates from 19 of the 20 mice inoculated with oocysts from the lambs but in none of the mice inoculated with oocysts from the cat.