EHV “Outbreaks”
Equine Herpesvirus (EHV) should be taken seriously. EHV can cause severe and debilitating illness; the neurological form of EHV can necessitate the euthanasia of affected horses. Prevention and vaccination should be priorities for all horse owners.
That said, EHV has been around for decades. It was first identified in the 1930s, long before your horse was born and it will be around after we are all gone. There is no evidence that EHV outbreaks are increasing in frequency. There is no evidence that the disease has become more lethal. There is no epidemic of EHV infection.
What’s more, most horses recover uneventfully from infection. Most horses do not get the neurological form of the virus. Most horse that do, recover. Many horses are already latently infected with the virus. These horses may be suffering minor, occasional recrudescence (return) of infection — now, yesterday, last month. Despite this recrudescence of infection, neither you, nor your horse, nor your vet even realized.
The point here is that it is important not to overstate the risk of EHV to our horses. The risk is small. Basic awareness and prevention are to be commended. Consulting your veterinarian about an EHV vaccination protocol is wise. But panicking, misjudging risk, or implementing overly broad prevention measures, doesn’t help anyone — not you and not your horse.
Take this example: A barn implements mandatory EHV testing for all new horses entering its facility. This barn takes a nasal swab from each new entering horse, sends the swab out for testing, and has the results back in 48 hours or less. These aren’t tests on animals showing signs of infection; there may be no fever and no respiratory distress. These are indiscriminate tests.
What’s the risk here? We know that EHV is ever present in the environment. We know that latently infected horses are commonly suffering recrudescence, shedding virus through their nasopharynx. A nasal swab taken on a horse suffering a minor infection will be positive for EHV. With the positive EHV swab, we have “EHV in the barn.” The horse or the whole barn might go under quarantine.
Never mind that, of course, there is EHV in the barn or that this sort of minor infection and viral shedding is going on constantly among our horses. We have a possible outbreak, another case to report in the news, and panic spreads. We’ve invented an “outbreak.”
Instead, the new horse could be isolated and monitored, as all new horses should, for a period of 21 days. After the isolation period ends without incident, the horse would be reintroduced to the barn without consequence. If the horse were to show signs of EHV we would know within the isolation time period, as the incubation period for both neurological and respiratory EHV is shorter than the 21 days. Isolation is a much more reasonable approach to dealing with the introduction of new horses to a barn.
I don’t know that the above scenario about testing has occurred in any given barn. I do know that there’s a lot of indiscriminate testing going on and in my opinion this represents bad policy. EHV is everywhere and there is a difference between true, serious infection and incidental infection. EHV outbreaks are real and serious. We don’t need to invent new ones.