A CROSS-SECTIONAL STUDY TO SHOW EPERYTHROZOON-OVIS INFECTION IS PREVALENT IN WESTERN AUSTRALIAN SHEEP FARMS

A serological survey and risk factor study was conducted to estimate the prevalence of Eperythrozoon ovis infection in Western Australian weaner sheep, the prevalence of farms with infected sheep, and to identify factors affecting initiation and maintenance of infection on the farm. The study was conducted on 91 farms, purposively chosen from 41 randomly selected regional shires stratified by sheep number and rainfall zones. Twenty sheep were selected systematically from a mixed-sex flock on each farm and tested for serum antibody to E ovis using an enzyme-linked immunosorbent assay. Information on putative risk factors was collected using an interview questionnaire. Antibody to E ovis was detected in 4.5% of sheep on 47% of the farms sampled. The prevalence of E ovis infection in sheep was estimated at the 95% confidence level to be between 3.6 and 5.5%, and the prevalence of farms with infected sheep was estimated to be between 37.5 and 56.5%. Most farms with serological evidence of infection occurred in the Great Southern agricultural region (79.5%), south-east of Perth through to Albany (latitude 32 to 34-degrees-S, longitude 116 to 120-degrees-E), and in the Northern region (12.8%) surrounding Geraldton (latitude 29-degrees-S, longitude 114-degrees-E). There were significantly more farms (P < 0.05) with evidence of infection in the Great Southern region compared to the Central region between Geraldton and Perth, and on farms in the region south compared to north of latitude 32-degrees-S. None of the putative risk factors examined in the questionnaire were associated with serological evidence of infection on the farm. The presence of E ovis infection in weaner sheep was largely unrecognised by farmers.