I haven’t written much about equine herpesvirus type 1 (EHV-1) outbreaks lately because I have a hard time getting excited about them (from a blog writing standpoint… if one occurs here, that will be a different story). Outbreaks of neurological disease caused by this very common equine virus (one that doesn’t spread to people or non-equids) continue to occur, and it’s hard to say whether we’ve been seeing more of them over the past couple of years or whether we’re just hearing about them more often. It does seem like outbreaks have truly become more common and more virulent in the past 10 years or so, but I’m not sure it’s continuing to get worse.
The latest EHV-1 outbreak has affected 5 of 7 horses on a central Minnesota farm. At last report, one horse had been euthanized and one was hospitalized at the University of Minnesota. The hospitalized horse is presumably receiving supportive care, such as intravenous fluids and general nursing support. Affected horses may become very weak and sometimes they need to be managed in a sling (see photo), since horses don’t tolerate being unable to stand for long (laying down for prolonged periods of time can damage muscles and nerves, simply because they are crushed by the horse’s own weight). Sometimes the bladder becomes paralysed and needs to be drained using a catheter. Numerous other problems can occur since the way this disease affects each horse can be quite variable. Fortunately, the prognosis tends to be reasonable (at least compared to other neurological disorders) if the horse is not severely infected and stays standing or is able to remain upright with the support of a sling. The clinical signs are the result of inflammation of the blood vessels in the brain and spinal cord, and the key is to get that inflammation down and keep the horse alive in the meantime.
In the past, we didn’t worry too much about these horses in equine hospitals. EHV-1 neurological disease tended to occur sporadically, not in the form of outbreaks, and dogma was that once the horse was sick, it wasn’t at much risk of shedding the virus. In fact, for a long time our best stall in the main hospital for neurological cases (which had padded walls, and a ceiling anchor for a sling) was right at the front of our main equine ward. A large outbreak in the US in the early 2000s changed that, and now we take much more aggressive measures to contain this virus, including housing affected horses in isolation and using strict infection control measures. With these precautions, the risk of spreading the virus in an equine hospital is low.
Image: A horse with neurological disease being managed in a sling (source: http://coloradodisasterhelp.colostate.edu)