Submitted to: Veterinary Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/6/2009
Publication Date: 5/19/2009
Citation: Fayer, R., Santin, M. 2009. Cryptosporidium xiaoi n. sp. (Apicomplexa: Cryptosporidiidae) in sheep (Ovis aries). Veterinary Parasitology. 164:192-200.
Interpretive Summary: Domestic food animals such as cattle, sheep, and pigs have a high prevalence of infection with protozoan parasites of the genus Cryptosporidium. Within this genus there are over 20 species of parasites, all extremely small even by microscopic standards, and most appear indistinguishable or nearly so when observed microscopically. Molecular methods are required to distinguish these species. Some of these species can be transmitted from animals to humans and pose a public health risk. It is therefore important to identify, characterize, and name species so that veterinarians, physicians, epidemiologists, and others involved in food and water safety can distinguish the pathogenic from the non-pathogenic species. The present study has characterized and named a new species found worldwide in domesticated sheep and has been named Cryptosporidium xiaoi. It has not been found to infect humans or to cause disease in sheep and therefore can be regarded as a non-pathogenic species of low risk for animals and humans. Therefore, finding it in relation to diarrheal disease in sheep should not be regarded by veterinarians as the underlying cause of the illness, and finding it as a contaminant of drinking water or on fresh foods should not be a cause for a boil water alert or for food condemnations.
Technical Abstract: A new species, Cryptosporidium xiaoi, is described from sheep. Oocysts of C. xiaoi, previously identified as the Cryptosporidium bovis-like genotype and as the ovine genotype from sheep in Australia and the United States are recorded as such in GenBank (AY587166, EU203216, DQ182597, AY741309, and DQ871345). Oocysts obtained from naturally infected sheep were infectious for a lamb and oocysts from that lamb were infectious for three other lambs. The prepatent period for C. xiaoi in these four Cryptosporidium-naïve lambs was 7-8 days and the patent period was 14-15 days. Oocysts are similar to those of C. bovis but slightly smaller, measuring 2.94-4.41 x 2.94-4.41 µm (mean = 3.94 x 3.44 µm) with a length/width shape index of 1.15 (n=25). Oocysts of C. xioai were not infectious for BALB/c mice, Bos taurus calves, or Capra aegagrus hircus kids. Fragments of the SSU-rDNA, HSP-70, and actin genes were amplified by PCR, purified, and PCR products were sequenced. The new species was distinct from all other Cryptosporidium species as demonstrated by multi-locus analysis of the 3 unlinked loci. Further evidence of species status was demonstrated by a lack of recombination. Based on morphological, molecular and biological data, this geographically widespread parasite found only in Ovis aries is recognized as a new species and is named Cryptosporidium xiaoi.