Prevalence of antibodies to Neospora caninum within central Queensland beef cattle.

Of the 1673 cattle tested, 249 (14.9%) were seropositive for N caninum. The mean seroprevalence of individual properties was 14.7% (SD = 8.6%). Of the 40 properties surveyed, only two (5%) did not have a seropositive animal among those tested. Age-related seroprevalence rates are illustrated in Figure 1 and show a seroprevalence of around 10% in heifers with a trend of increasing seroprevalence with age. This is the first seroepidemiological report of N caninum in Australian beef cattle. The results suggest that N caninum is endemic in beef herds across central Queensland. Seroprevalences reported for beef cattle in overseas surveys vary from 2.8% in New Zealand4 to 24% in northwestern USA.5 The reasons for the comparatively high seroprevalence in central Queensland cattle are not known, but may include the presence of a significant population of wild dogs and dingoes in this grazing region (which may act as definitive hosts for the parasite6), environmental factors (such as factors influencing the survival of oocysts in the environment, the degree of contact between wild canids) and less rigorous culling of cattle that fail to rear a calf every year compared with intensive beef production regions. Age-related seroprevalence in the central Queensland herds suggests that both horizontal and vertical transmission is occurring (Figure 1). The gradually increasing age-related seroprevalence is suggestive of horizontal transmission, presumably from a definitive host. The seroprevalence of around 10% observed in the younger stock suggests that congenital transmission also plays a part in the natural history of N caninum infection in beef herds. The study design meant that in every herd, one third of all samples taken were from 1to 2-year-old cattle. The comparatively greater numbers sampled in these age groups means that confidence limits on these means are relatively narrow. The determination of the confidence limits did not take clustering within herds or age groups into consideration. However, even considering this, the data do suggest that the seroprevalence in the 1 to 2 year age group is significantly higher than 0. This pattern of transmission offers promise for parasite control programs. If seropositive animals were removed from breeding groups, then the overall prevalence on a property would be expected to decline significantly because the rate of Prevalence of antibodies to Neospora caninum within central Queensland beef cattle