Epidemiology of Neospora caninum in dairy cattle and wild canids on Prince Edward Island

The main aim of the studies described in this thesis was to obtain more epidemiological information on Neospora caninum and the purported sylvatic life cycle of this parasite.

The significance of N. caninum in dairy herds on Prince Edward Island (PEI) is reported in Chapter 2, by testing bulk milk samples. The prevalence of dairy farms with a within-herd seroprevalence ≥15% on PEI was 10.2% in June 2005. In 11 farms that were considered positive based on bulk milk samples, blood samples were collected of all adult cows in September 2005, in conjunction with a fourth bulk milk sample on the same day. The results of this study demonstrate that the prevalence of N. caninum in dairy farms can be estimated using a bulk milk enzyme linked immunosorbent assay (ELISA).

Three ELISAs, 2 indirect fluorescent antibody tests (IFATs) and 1 N. caninum agglutination test (NAT) were compared using sera of randomly collected dairy cattle from Atlantic Canada. One IFAT performed well (sensitivity and specificity: 0.97 and 0.97) using reference sera, therefore results from this IFAT could subsequently be used as reference standard to calculate test characteristics for the other assays. Sensitivity was ≥0.89 for all assays except the NAT which had a significantly lower sensitivity (0.66). Specificity was high (>0.94) for all assays except for one indirect ELISA (specificity=0.52). The performance characteristics observed for most assays in this study (Chapter 3) make them useful for screening antibodies to N. caninum in cattle.

The effect of hemolysis on serological assays was studied in Chapter 4 and demonstrates that an indirect ELISA produced better test characteristics using hemolysed fox sera. A competitive ELISA had the advantage of not being species specific, and performed equally well with non-hemolysed sera from cattle and foxes. However, caution is required when using this competitive ELISA with hemolysed fox sera, because it had a significantly reduced specificity.

Chapter 5 describes the population structure and habitat characteristics of wild canids on PEI. The average age of foxes was 1.5 years (range 0.5-13.5, median 0.5) and for coyotes 2.1 years (range 0.5-13.5, median 1.5). The proportion of juvenile (less than a year of age) foxes and coyotes was 58 and 48%, respectively. The observed sex-ratio was equal, and average litter size for foxes and coyotes was 5.0 (range 0-7) and 5.2 (range 0-11), respectively. The main habitat for foxes was agricultural land and forest was the main habitat for coyotes.

Chapter 6 documents the occurrence of antibodies to N. caninum in wild canids from PEI, however the observed seroprevalence in foxes (2.6%) and coyotes (2.5%) was low. The serologic evidence of N. caninum infection in the foxes and coyotes poses questions about the relative importance of transmission of N. caninum between wildlife and livestock.

Chapter 7 describes the findings of oocysts morphologically and morphometrically similar to oocysts of N. caninum in 2 fox and 2 coyote fecal samples. DNA was extracted from these samples and found positive on nested PCR utilizing primers to the N. caninum-specific Nc5 genomic sequence. PCR using primers specific for Hammondia heydorni failed to yield an amplification product from these DNA samples.