Rabies Has Many Faces

Rabies. The word conjures up chilling images from old movies: a snarling dog, foaming at the mouth, attacking anything that moves. But did you know horses are very susceptible to this disease?

Skunks, foxes, bats, and raccoons are the main wild animals that transmit rabies. These all can live in habitats bordering typical horse farms. Wild animals with rabies behave abnormally, and as horses are curious, it is easy to imagine how they can be bitten by a rabid wild carrier. A single bite can transmit enough virus to kill.

Once a horse shows signs of rabies it invariably dies within a few days. Early signs range from colic and lameness to depression and agitation. There is no treatment. Horses with rabies are a great risk to their handlers, as saliva from an affected horse carries virus that can potentially transmit the disease to a person.

New York State has reported 51 cases of horse rabies over the past 19 years. I was involved in diagnosing three of them. All were fatal. All were very different, illustrating that rabies can "look like anything."

The first was a mare living in a pasture bordering a wooded area. Her owners called, saying she was "bellowing like a pig" and acting strangely. When I asked about her rabies status I was told she had never been vaccinated.

On arrival I found the mare in a pen. Long ropes of drool dripped from her mouth. She was tossing her head, flinging saliva everywhere. She had chewed a large hole in one leg through the skin (presumably where she was bitten and exposed). Her aggression was terrifying--she would attack anyone and anything that came near her. Strongly suspecting rabies, I convinced the family to put her to sleep. Subsequent testing confirmed the disease. The family members and I underwent post-exposure immunization.

Case number two was very different. This horse was seen at a routine appointment because she just wasn't right. I did a physical exam and found nothing major other than a mild fever and dull attitude. I opened her mouth during the exam and handled her tongue and gums. I took some blood and prescribed anti- inflammatories. The next day the owner called back--overnight the mare had lost the ability to swallow and she was getting wobbly. She was sent to Cornell for advanced care, but her condition deteriorated and she became recumbent. She was euthanized. She had never been vaccinated for rabies and was found positive for the disease. More than 20 people from the farm and Cornell required post-exposure treatment, including me.

The third case involved a 3-year-old gelding experiencing difficulty walking. Our practice's intern found the horse was febrile, had signs of colic, and had some incoordination in his hindquarters. We monitored him for several hours; his signs varied--he would fall down and act painful and wobbly, get up and act seminormal, then repeat the cycle. Over time he got worse and that evening he became recumbent. We queried his vaccination status and were told that he was purchased from someone out West who "gave him all his shots." We later found out he had not been vaccinated against rabies because it was not considered a problem disease in his state of origin. The horse was euthanized that night and confirmed rabid the next day. Eight people who handled the horse (including me and our practice intern) pursued post-exposure treatment.

If there is a bright spot in this story, it is that modern vaccines are very effective in providing rabies immunity. The American Association of Equine Practitioners has recently listed rabies as one of the "core vaccines" that should be given to all horses. Current recommendations are to begin immunization when a foal reaches 6 months of age, then follow with a booster dose in four to six weeks. Horses should then receive boosters at annual intervals starting at 10 to 12 months of age. Broodmares should be vaccinated four to six weeks prior to their delivery dates. Most state health departments mandate that the vaccine be given by a licensed veterinarian who will keep detailed records on the vaccination history of the horse.

And just to be safe ... if your horse starts acting odd, please don't put your hands in his mouth! Strange behavior is always a valid reason to call your veterinarian.

About the Author

Ann Dwyer, DVM

Ann Dwyer, DVM, is a practitioner at the Genesee Valley Equine Clinic in Scottsville, N.Y.

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