Bovine herpesvirus-1 in three major milk sheds of Ethiopia: Serostatus and association with reproductive disorders in dairy cattle

Bovine herpesvirus-1 (BHV-1) causes infectious bovine rhinotracheitis (IBR), and infectious pustular vulvovaginitis (IPV) in cows and infectious pustular balanopostitis (IPB) in bulls worldwide. Infection of seronegative cattle with BHV-1 leads to abortion, retention of fetal membranes, increased service per conception, metritis and oophoritis. As part of an ongoing study on infectious causes of reproductive disorders in Ethiopia, this investigation aims at assessing the role of BHV-1 in the disorders and the risk factors affecting its seroprevalence. A cross-sectional study was conducted on a total of 1379 randomly selected dairy cattle from 149 herds. These dairy cattle were sampled from milks sheds of central (n = 555), western (n = 195) and southern (n = 629) Ethiopia. Blocking enzyme-linked immunosorbent assay (B-ELISA) was applied to detect antibodies specific to BHV-1. Additionally, a semi-structured questionnaire was administered and farm records were assessed to capture potential risk factors associated with BHV-1 seropositivity. Univariable and multivariable random-effects logistic regression analyses were used to assess potential risk factors associated with BHV-1 serostatus. Model fitness and reliability were assessed using the Hosmer and Lemeshow method and the receiver operating curve (ROC) respectively. An overall herd level BHV-1 seroprevalence of 81.8% (95% confidence interval (CI): 74.7-87.7%) and individual animal level seroprevalence of 41.0% (95% CI: 38.4-43.7%) were found. In a random-effects multivariable logistic regression model, the seroprevalence of BHV-1 exposure was higher in dairy cattle from breeding (Odds ratio [OR] = 1.3; p = 0.036) than in commercial (OR = 0.9; p = 0.137) and small-holder farms. Geographically, the prevalence was higher in western (OR = 1.4; p < 0.001) and southern Ethiopia (OR = 1.2; p < 0.001) than in central regions. BHV-1 seropositive cows had higher (p < 0.05) odds of clinical reproductive disorders including abortion, retained fetal membranes, stillbirth, birth of weak calf and metritis compared to seronegative cows. Thus, it is suggested that BHV-1 should be considered as differential diagnosis among improved dairy cattle herds with reproductive disorders in Ethiopia.