A longitudinal study of Giardia duodenalis genotypes in dairy cows from birth to 2 years of age.

Fecal specimens were collected from 30 calves from birth to 24 months of age at a dairy farm in Maryland to determine the prevalence of Giardia duodenalis genotypes in cattle of different ages. Fecal samples were subjected to density gradient centrifugation to remove debris and concentrate cysts. Specimens were analyzed by immunofluorescence microscopy and polymerase chain reaction (PCR). All PCR positive specimens were sequenced using the SSU-rRNA gene of Giardia. All 30 calves shed G. duodenalis cysts at some time during the study. Of 990 specimens, 312 were positive for G. duodenalis (31.5%). The highest prevalence of infection occurred at weeks 4 and 5 of age with 25 out of 30 calves shedding cysts at those sampling times. Overall, pre-weaned calves (<8 weeks of age) exhibited the highest prevalence (60.8%), followed by post-weaned calves (3-12 months of age) (32.1%) and heifers (12-24 months of age) (11.4%). Sequence analysis of the 312 PCR-positive samples revealed the presence of both Assemblages A and E, G. duodenalis, with cumulative prevalences of 70% and 100%, respectively. Assemblage A was not detected in pre-weaned calves, but was detected in 6.9% and 4.7% of post-weaned calves and heifers, respectively. These data indicate not only that calves are infected with both Assemblages A and E simultaneously, but also that infections with zoonotic Assemblage A, G. duodenalis are more common than previously reported. Thus, calves appear to be a more significant reservoir of human infectious G. duodenalis than previous data have suggested.