Detection of EHV-1 and EHV-4 in placental sections of naturally occurring EHV-1- and EHV-4-related abortions in the UK: use of the placenta in diagnosis.
Authors: Gerst S, Borchers K, Gower S M, Smith K C
Journal: Equine veterinary journal
Summary
# Editorial Summary: Placental Examination in EHV Abortion Diagnosis When investigating equine herpesvirus-related abortions, practitioners and veterinarians often face a diagnostic challenge: the fetus may be unavailable, decomposed, or unsuitable for examination, yet establishing the aetiological agent remains crucial for herd management and infection control. Gerst and colleagues addressed this gap by evaluating whether placental tissue alone could reliably detect and differentiate between EHV-1 and EHV-4 using molecular and immunological techniques on allantochorion samples from 49 naturally occurring herpesvirus abortions. PCR successfully identified viral DNA in 46 cases (41 EHV-1, 5 EHV-4, with 2 samples positive for both viruses), whilst in situ hybridisation localised EHV-1 DNA in 21 cases and EHV-4 in 4 cases; immunohistology detected viral antigen in 15 cases, predominantly within endothelial cells of chorionic villi and occasionally in trophoblast epithelium. The findings demonstrate that placental examination is a reliable diagnostic tool that should be incorporated into standard abortion investigations, particularly when fetal tissue is unavailable—a pragmatic recommendation that could improve diagnostic yield and inform biosecurity decisions on affected premises.
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Practical Takeaways
- •Placental examination should become routine in equine abortion investigations, especially when the fetus cannot be submitted for necropsy
- •PCR analysis of placental allantochorion is highly sensitive for detecting EHV-1 and EHV-4 viral DNA and can differentiate between the two viruses
- •In cases of suspected herpesvirus abortion with only placenta available, send placental samples for PCR, in situ hybridisation, and immunohistology to confirm diagnosis
Key Findings
- •PCR detected viral DNA in 46 of 49 placental samples (41 EHV-1, 5 EHV-4, 2 mixed infections)
- •In situ hybridisation identified EHV-1 DNA in 21 cases and EHV-4 in 4 cases from PCR-positive samples
- •Immunohistology detected viral antigen in 15 cases, primarily in endothelial cells of chorionic villi and trophoblast epithelium
- •Placental examination provides a useful diagnostic alternative when fetal tissue is unavailable for EHV-1 and EHV-4 abortion diagnosis