Questions applications and conclusions in equine herpesvirus study
I enjoyed the article1 by Dr. Allen in the August 2006 AJVR titled “Antemortem detection of latent infection with neuropathogenic strains of equine herpesvirus-1 in horses,” but I believe there are problems in the practical application and with some conclusions with the study. The study did help in other ways.
First, I have concerns about the practical applications. The horses were anesthetized to be able to harvest lymph nodes. I doubt that owners will allow a shed row of horses to be laid down if they are clinically normal, as were the horses in the study. In addition, if a horse may be on the edge of developing abnormal neurologic signs, putting them in recumbency is not going to help. For example, if it turns out to be West Nile virus infection, they may not get up after a harvest.
Second, there are problems with the conclusion. The authors of the study say the tests may help in a “test-and-segregate” strategy to minimize the risk of outbreaks. If they can test positive for years after inoculation, how will you ever be able to clear them for transport when they never had clinical signs of infection? How can we determine whether horses were infected recently or years ago? The presence of the neurologic form of the virus only proves exposure and not necessarily disease. Imagine if all horses exposed to equine protozoal myeloencephalitis had to be segregated from an infected horse. The presence of this form of equine herpesvirus-1 (EHV-1) in a clinically normal horse does not make it a time bomb.
As mentioned, I did find the study helpful in places. The ability to isolate this form of EHV-1 may help with future vaccines. Also, conventional PCR testing underestimates true prevalence of infection, and the study describes an improved test.
Evidence of latent neuropathogenic EVH-1 infection in a horse does not mean it is diseased. Horses can be infected for years (4 to 5 years in this study) with no problems, much like infection with the respiratory form. So, it seems we need to understand that the presence of infection in a horse is not a panic button issue and should not be used to segregate them from other horses.
Frank K. Reilly, DVM
Equine Medical & Surgical Associates Inc, West Chester, Pa
Allen GP. Antemortem detection of latent infection with neuropathogenic strains of equine herpesvirus-1 in horses. Am J Vet Res 2006;67:1401–1405.
