Morphological and genetic characterisation of Cryptosporidium oocysts from domestic cats.

Faecal samples were collected from domestic cats in the metropolitan area of the city of Perth, Western Australia, and screened for the presence of Cryptosporidium by both microscopy and PCR. Of 162 samples screened, two were positive for Cryptosporidium (a prevalence of 1.2%). Sample Ct33 was from an 18-month-old female and sample Ct131 from a 12-month-old female. Morphological studies revealed oocysts with an average size of 4.6 x 4.0 microm, smaller in size than isolates typically seen in humans (5.0 x 4.5 microm). Sequence analysis of PCR products showed sequences from cat isolates to be different to previously sequenced human and calf isolates, with cat isolates exhibiting 8.1% sequence divergence from these isolates. Phylogenetic analysis grouped the cat isolates into a distinct group, separate from other C. parvum isolates and Cryptosporidium species. These results lend support to the existence of a cat-adapted Cryptosporidium strain or species.