Background: Cryptosporidium and Giardia are important causes of diarrhea diseases in humans and animals worldwide, and both of them are transmitted by the fecal-oral route, either by direct contact or by the ingestion of contaminated food or water. The role of flies in the mechanical transmission of Cryptosporidium and Giardia has been receiving increasing attention. To date, no information is available in China about the occurrence of Cryptosporidium and Giardia in flies. We here investigated Cryptosporidium and Giardia in flies on dairy farms in Henan Province, China, at the genotype and subtype levels.
Methods: Eight hundred flies were randomly collected from two dairy farms from July 2010 to September 2010 and were divided evenly into 40 batches. The fly samples were screened for the presence of Cryptosporidium and Giardia with nested PCR. Cryptosporidium was genotyped and subtyped by analyzing the DNA sequences of small subunit rRNA (SSU rRNA) and 60-kDa glycoprotein (gp60) genes, respectively. The identity of Giardia was determined by sequence analyzing of the triosephosphate isomerase (tpi), glutamate dehydrogenase (gdh), and β-giardin (bg) genes.
Results: Forty batches of flies had 10% of contamination with Cryptosporidium or Giardia, with a mixed infection of the two parasites in one batch of flies. The Cryptosporidium isolates were identified as C. parvum at the SSU rRNA locus, and all belonged to subtype IIdA19G1 at the gp60 locus. The Giardia isolates were all identified as assemblage E of G. duodenalis at the tpi, gdh, and bg loci. One novel subtype of assemblage E was identified based on the gdh and bg loci.
Conclusions: This is the first molecular study of Cryptosporidium and Giardia in flies identified at both genotype and subtype levels. SSU rRNA and gp60 sequences of C. parvum in flies was 100% homologous with those derived from humans, suggesting flies act as an epidemiological vector of zoonotic cryptosporidiosis. The variable PCR efficiencies observed in the analysis of Giardia at different loci suggest that we should use the multilocus genotyping tool in future studies to increase the detection rate, and importantly, to obtain more complete genetic information on Giardia isolates.