Serological survey of maedi-visna virus infection in highland sheep at ranches and smallholder farms in eastern Amhara region, Ethiopia

A cross-sectional study was conducted to determine the prevalence and associations with potential risk factors of Maedi-visna virus infection in the Ethiopian highland sheep of the eastern Amhara region. A total of 2417 sheep were examined between December 2005 and March 2006. Of these, 926 sheep were from semi-intensive production system (ranches) composed mainly of Awassi and indigenous Menz sheep breeds while 1491 sheep were from extensive system (smallholder farms) with indigenousbreeds being predominant. Indirect-Enzyme Linked Immunosorbent Assay and Agar Gel Immunodiffusion tests were employed in parallel to determine the presence of antibodies against maedi-visna virus infection.The overall individual animal-and flock-level prevalence was 15.6% (95%CI: 14.1-17.1) and 25.9% (95%CI: 20.8-31.5), respectively. Maedi-visna seroprevalence was higher in sheep at ranches with prevalence of 30% and 86.2% at individual- and flock-level. A Prevalence of 6.6% and 18.8% was found in smallholder farms at individual- and flock-level, respectively. The prevalence difference was highly significant (P < 0.001) between the sheep production systems. Breed, flock size, age, sex, and husbandry practices were significantly associated with maedi-visna seropositivity. Higher risk to infection was found in Awassi breed and theircrosses than indigenous sheep. Breed management systems, but not breed caused susceptibility variation. The husbandry and management systems, old and large flock sizes in ranches were found important riskfactors associated with higher rate of infection. Sheep breeding ranches could serve as a source of Maedivisna virus infection to smallholder farms along with the distribution of rams and effective control measureshave to be implemented through annual testing and culling of seroreactors and raising lambs artificially in isolation. Screening tests aiming at culling seropositive animals should be carried out during introduction ofnew flocks and before distribution of rams to smallholder farms