Equine Herpesvirus 1 and 4 Respiratory Disease in the Horse
Authors: Harless Wendy, Pusterla Nicola
Journal: Clinical Techniques in Equine Practice
Summary
# Editorial Summary: EHV-1 and EHV-4 Respiratory Disease in the Horse Distinguishing between equine herpesvirus types 1 and 4 in vaccinated populations has proven diagnostically challenging, particularly when inactivated EHV-1 vaccines are widely used in racing environments. Harless and Pusterla developed and evaluated a type-specific ELISA using glycoprotein G antigens to overcome this limitation, comparing its performance against the traditional complement-fixation test across experimentally vaccinated horses and naturally exposed racehorses at two Japanese training centres. Crucially, whilst the CF test generated false-positive responses to inactivated vaccine administration (with elevated antibody titres in 38 vaccinated horses), the glycoprotein G ELISA failed to detect vaccine-induced antibodies, allowing it to distinguish genuine EHV-1 and EHV-4 infections even in vaccinated populations. This diagnostic capability is particularly valuable for identifying natural exposures and tracking disease epidemiology in high-risk racing yards where vaccination is routine. Practitioners involved in respiratory disease investigation and surveillance programmes should consider type-specific ELISA as a more reliable serological tool than complement-fixation testing when working with vaccinated horses.
Read the full abstract on PubMed
Practical Takeaways
- •Use type-specific ELISA rather than complement-fixation testing for accurate serological diagnosis of EHV-1 versus EHV-4 in vaccinated racehorses, as inactivated vaccines do not trigger detectable ELISA antibody responses
- •This diagnostic approach enables reliable epidemiological tracking of natural EHV infections in vaccinated racehorse populations without false positives from vaccine antibodies
- •Consider implementing type-specific ELISA for monitoring EHV status in training centers and racing operations to identify circulating virus types and inform vaccination strategy
Key Findings
- •Type-specific ELISA using EHV glycoprotein G can distinguish EHV-1 from EHV-4 infections in both vaccinated and unvaccinated horses
- •Inactivated EHV-1 vaccine elicited detectable antibody response by complement-fixation test but not by type-specific ELISA in 6 experimentally vaccinated horses
- •In 38 racehorses receiving intramuscular inactivated EHV-1 vaccine twice at 4-week intervals, CF test showed increased titers but ELISA did not detect vaccine-induced antibodies
- •Type-specific ELISA successfully differentiated EHV-1 and EHV-4 infections in paired sera from vaccinated racehorses during winter season monitoring