Infection dynamics of and in a Swedish dairy herd.

In order to investigate the infection dynamics of and , a Swedish dairy farm known to be free of was recruited for a one-year study. Fecal samples were collected every four weeks (a total of 13 occasions) from 20 randomly selected calves younger than 65 days. A total of 238 feces samples were collected directly from the rectum and then examined with immunofluorescence microscopy; those positive for spp. oocysts were further processed by molecular species determination. Oocysts were found in 92 samples, and in 72 of these the species was successfully determined: 87.5% 9.7% and 2.8% a mix of both species. No was found. The prevalence of shedding calves was highest at ages 4 and 5 weeks; however, the feces with the highest oocyst per gram (OPG) were registered at 2-4 weeks of age. This is earlier than what has been found in most other studies, indicating that the infection dynamics of may be affected by the presence of . The OPG for the positive calves ranged from 200 to 1.1 × 10 (geometric mean 6.88 × 10). The youngest calf in which was identified was 5 days old, and the youngest calf in which was identified was 15 days old. Calves' housing type and seasonality were not associated with differences in the shedding of oocysts. Furthermore, there was no association between the presence of diarrhea and oocyst shedding.