The Ontario Ministry of Agriculture Food and Rural Affairs has issued a Biosecurity Alert (2015-07-09 EHM advisory) in response to an equine herpesvirus myeloencephalopathy (EHM) case. This neurological disease, caused by equine herpesvirus type 1 (EHV-1) gets a lot of attention now, when 10 years ago it would have largely been dismissed (or at least not caused a lot of concern). Back then, we regularly saw sporadic cases and we just managed them where they were. However, in the intervening years, large outbreaks have been widely reported, so we’re a lot more careful now. Whether that’s because the disease is changing or we’re doing a better job of identifying and reporting outbreaks isn’t clear (it’s probably a bit of both). Regardless, while most cases of EHM are just single, sporadic incidents, we tend to be fairly aggressive to try to prevent a bigger problem from developing.
EHV-1 is a hard virus to completely control. It lives dormant in a large percentage of healthy horses (herpes is forever, as they say), and rarely causes disease in most. So, testing for carriers amongst the general population or trying to eradicate it aren’t realistic options. Rather, we focus on good routine infection control practices and good infection response.
In this case, there will presumably be close monitoring of any in-contact horses, potentially with short term isolation or movement restrictions. As with most infectious diseases, it’s best to be aggressive early in the course of a situation while you’re getting a handle on the problem, then relax those restrictions later on when deemed appropriate. That’s better than the opposite “I hope it will get better” approach of doing little at the start, and trying to play the odds that an outbreak won’t develop. That is when disaster will usually strike…
Hopefully this is the last we here of this situation, but the next week will be informative.