Seroprevalence of Schmallenberg virus in dairy cattle in Ethiopia

Schmallenberg virus (SBV) is a recently identified member of the genus Orthobunyavirus of the family Bunyaviridae. It is an arbovirus transmitted by different members of Culicoides spp of biting midges. The virus is more recognized for its effect on reproductive disorders in ruminants characterised by abortion, stillbirth and birth of congenitally defective newborns with hydranencephaly-arthrogryposis syndrome. The current study was undertaken with the objectives of exploring the presence of SBV exposure and identification of factors affecting its distribution among dairy cattle in Ethiopia. A cross-sectional study was conducted on 1379 dairy cattle sampled from 149 dairy herds in central, southern and western Ethiopia during September 2011 to May 2012. Serum samples were examined using competitive enzyme linked immunosorbent assay (cELISA). Data on hypothesised risk factors were collected from farm records where available and semi-structured questionnaire-based interview. The apparent seroprevalence of exposure to SBV was 56.6% (95% confidence interval (CI): 53.9-59.3). True prevalence adjusted for sensitivity and specificity of the cELISA kit used was 58.3% (95% CI 55.7-60.9). Among the sampled herds, 82.6% (95% CI: 75.5-88.3) had at least one seropositive animal. Seropositive cattle were found in all of the 15 conurbations studied. Adult dairy cows [odds ratio (OR)=1.6] were more commonly affected than young heifers. Dairy cattle kept in commercial (OR=1.6) and breeding farms (OR=3.5) and Midland agroecology (OR=2.5) showed statistically significant seroconversion than cattle kept under small-holder dairy farms and Highland agroecology respectively (p<0.05). Reproductive disorders including abortion, retention of the fetal membranes, and metritis were associated with serostatus of SBV. In conclusion, the seroprevalence of SBV is high and widely distributed in the studied parts of Ethiopia. This being the first study of its kind on SBV in Ethiopia, further longitudinal studies on isolation of the virus and its impact on reproductive disorders are recommended.