Role of equine herpesviruses as co-infecting agents in cases of abortion, placental disease and neonatal foal mortality

Herpesviral infections frequently occur in horses. The objective of this study was to investigate the possible association of equine herpesviruses (EHV-1, EHV-2, EHV-3, EHV-4, EHV-5) with other causes of abortion, neonatal mortality or placental disorder. Sixty-seven abortions, 22 stillbirths, 14 cases of neonatal foal mortality and 3 cases of placental disease were investigated for infectious and non-infectious causes. Type-specific nested PCR assays and virus isolation were performed to detect EHV infections. A cause of fetal loss or placental disease was reached in 68 out 116 (58.7%) cases. Twenty-seven cases were positive for EHV, and 22/27 (81.5%) were positive for EHV-1 (16 neuropathogenic and 6 non-neuropathogenic strains), 4 (14.8%) for EHV-2 and 3 (11.1%) for EHV-5. The association between EHV infections and other etiological agents was statistically significant (two sided P = 0.002). The odds ratio of EHV DNA associated with other diagnoses, especially with bacterial infection and premature placental separation, was 10.88 (95% confidence interval: 2.15-55.16). EHV-1 was the main viral cause of pregnancy loss in this study, also associated with other etiological agents, including EHV-2 and EHV-5. The latter viruses in particular need to be more fully investigated to elucidate what role either or both may play as co-infecting agents with other established infectious causes of reproductive disease.