Submitted to: Veterinary Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/22/2008
Publication Date: 11/1/2008
Citation: Barigye, R., Khaitsa, M.K., Schamber, E., Dyer, N.W., Newell, T.K., Trout, J.M., Santin, M., Fayer, R. 2008. Molecular and Immunohistochemical Detection of Assemblage E Giardia duodenalis in Scouring North Dakota Calves. Veterinary Parasitology. 157(34):196-202. Interpretive Summary: Calves that were either affected by severe diarrhea or who had died after a bout of severe diarrhea were submitted for testing. Tests were conducted to determine the cause of the diarrhea. A commercial available test revealed the presence of Giardia in 22 of the infected calves. Research based tests, the polymerase chain reaction and DNA sequence analysis, were then performed to confirm the presence of Giardia and to determine if the Giardia was a type that could be transmitted to humans. Intestinal tissues were also collected and processed with special stains to determine if the infections were causing any damage to the tissues. Giardia was identified as the only cause of infection in a number of animals. The intestinal tissues showed that the infection had cause significant tissue damage and Giardia parasites were also visible in the tissues. The research based test showed that the Giardia was a type that does not infect humans, but only infects hoofed-livestock. These results indicate that diagnosticians should test for Giardia in calves with diarrhea, especially tests for other pathogens are negative. Because Giardia can cause damage to intestinal tissue, consideration should be given to treating Giardia infections with available medications.
Technical Abstract: Tissue and/or fecal samples were collected from scouring calves that were submitted to the North Dakota State University, Veterinary Diagnostic Laboratory. The samples were tested for presence of Giardia antigens using a SNAP Giardia-antigen test kit. To confirm a positive diagnosis, all Giardia-antigen-positive samples were subjected to a Giardia-specific polymerase chain reaction (PCR) testing was performed using primers to the ssu-rRNA gene; DNA sequencing was performed on all positive samples to determine the genotype of Giardia in the sample. For bacteriologic culture, intestinal contents were inoculated on a tryptose soy agar (TSA) II; samples were also inoculated on Skirrows media and incubated under anaerobic conditions. Frozen intestinal sections were tested by direct immunofluorescent antibody (FA) test to detect antigens from bovine virus diarrhea virus, rotavirus and coronavirus. Samples from different segments of the small and large intestine were taken, fixed in 10% buffered formalin, processed routinely and paraffin embedded. Five-micron sections were deparaffinized, stained with hematoxylin and eosin (H&E), and examined by light microscopy. Other deparaffinized sections were stained with a polyclonal anti-Giardia IgG antibody of goat origin. Giardia-positive samples represented 11.6% of all the scour cases in which an enteric pathogen was identified during the study period. All of the Giardia positive cases (95%) were aged between 1 and 4 weeks. Histological evaluation revealed changes characteristic of enteritis, including infiltration of inflammatory cells and sloughing of enterocytes; numerous trophozoites were also present. DNA sequence analysis revealed the presence of the livestock-specific Assemblage E, Giardia duodenalis. Giardia was the sole infectious agent in a number of calves with scours and all of the infections in the study were caused by Assemblage E, These data suggest that diagnosticians should screen for Giardia in scouring calves especially those testing negative to other enteric pathogens. Our data also indicate that IHC may be a useful diagnostic tool for confirming a Giardia diagnosis in scouring calves. The benefits of treating giardiasis in scouring neonatal calves with anti-protozoal agents need to be revisited and thoroughly evaluated.