Submitted to: Journal of Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 14, 2001
Publication Date: February 1, 2002
Interpretive Summary: Within specific hosts such as humans, mice, pigs, marsupials, dogs and ferrets several unique types of Cryptosporidium have been identified based on their gene sequences. However, the parasites possessing each genotype are indistinguishable from one another when observed microscopically, restricting our ability to clearly identify them as species and to be able to predict, when they are found in the environment, both their source and their potential to infect humans and livestock. The present study has characterized Cryptosporidium from a dog based on morphology, host specificity, biological characteristics, and gene sequencing, and has compared these characters with those of other isolates. Findings indicate that the isolate from domestic dogs is a unique species.
Oocysts of Cryptosporidium, spontaneously excreted after a dog was chemically immunosuppressed, were examined by bright field, differential interference contrast, and immunofluorescence microscopy and were found indistinguishable from oocysts of Cryptosporidium parvum. Sequence data for the 18S rDNA and the HSP-70 gene revealed sequences that varied significantly from all known species of Cryptosporidium. These oocysts, isolated from feces of the dog, were intubated into BALB/c neonatal mice, immunosuppressed C56BL6/N juvenile mice and a newborn Holstein calf. Oocysts of a bovine isolate of C. parvum were likewise intubated into controls for each of the same animal species. Based on microscopic examination of feces all animals became infected and excreted oocysts. However, by molecular analysis, the calf was the only animal confirmed to be infected with the canine isolate. Based on the genetic distances and differences in host specificity between the dog genotype and C. parvum genotypes, we therefore regard this unique organism as a separate species and propose the name Cryptosporidium canis.