CARE AND TREATMENT
Beyond rest and supportive care, there’s no specific treatment for rhinopneumonitis, but medication to control high fever can be beneficial. “NSAIDs [non-steroidal antiinflammatory drugs] that reduce fever will also make the horse feel better,” says Amy Johnson, DVM, DACVIM, of the University of Pennsylvania.
“We generally use either phenylbutazone [bute] or flunixin meglumine [Banamine].” Antibiotics may also be prescribed if a secondary bacterial infection develops.
For an isolated case or when affected horses show nothing more than respiratory illness, no further measures are likely needed. However, antiviral treatment may be recommended if a horse has been exposed to others who developed neurological signs. Antiviral medications help reduce the amount of virus in the bloodstream, which may reduce the risk of neurologic complications. “We can use a variety of drugs, including anti-inflammatory drugs, anti-thrombotic [anti-clotting] and antiviral drugs, that reduce the likelihood of that infected horse to eventually develop EHM,” explains Nicola Pusterla, DVM, PhD, of the University of California, Davis. “We can have significant impact on the outcome by using specific drugs. Many of these drugs have been in use for a long time, but we didn’t know that these could have a beneficial effect on EHM. For instance, anti-inflammatories have been shown to reduce cellular interactions between infected lymphocytes and endothelial cells of the central nervous system.”
Recent studies suggest that aspirin increases a horse’s chances of recovering from EHM. And the antiviral drug valacyclovir has shown some promise both as a prophylactic and in treating ill horses. “If we have an outbreak situation and have horses that we believe may have been exposed, we do treat them with valacyclovir in the hope that if they already have the virus within their body,
this drug will decrease its ability to replicate— and therefore reduce the chance that the horse will get neurologic disease,” says Johnson. “There is some evidence that this drug may also be helpful if given when the horse just starts to show neurologic signs, very early in the course of the disease.”
Once neurological signs develop, they may progress quickly, reaching their peak within 24 to 48 hours. At this point, the horse will require more intensive supportive care. “A lot of this is just making sure the horse is eating and drinking well and has normal hydration, and is able to urinate,” says Johnson.
If the horse can remain on his feet, his chances of a full recovery are good—the inflammation will subside and the injured tissues will eventually heal. The outlook is cloudier for horses who go down. “With any neurologic disease, if the horse is severely affected—enough to become recumbent—the long-term prognosis is considered worse than if the horse can remain standing,” says Johnson.
If a horse becomes impaired to the point where he is at risk of falling or he is fully recumbent, he may benefit from being placed in a sling to keep him on his feet. “This kind of support can be an important part of management,” says Johnson. “There have been cases in which horses have become totally recumbent and still recovered enough function to be ‘normal’ out at pasture. There may be some residual deficits that prevent that horse from going back to an athletic career, but his life could be saved. If an owner is devoted to that horse and wants to try to save him, even if he is recumbent, we usually try to keep him going and see how much function he can regain.”
It is important to maintain strict isolation throughout the course of a horse’s illness and even for up to three weeks afterward. “Back when I was in school, we thought that by the time a horse was showing neurologic signs he was no longer contagious,” says Johnson.
“We now know that horses with the neurologic form of the disease are very contagious.”