Rabies in Horses

With some foresight and simple preventive strategies that include annual vaccination of all horses on your property, equine rabies is preventable.
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Credit: Thinkstock The main hosts of rabies in the United States are raccoons, skunks, bats, foxes and coyotes, in that order.

Until recent decades, the risk of rabies in horses remained localized to very specific geographic locations. But the tide has been changing, with rabies becoming more prevalent in not just bats, but also in terrestrial mammals such as the skunk, fox, raccoon and coyote. This increase in wild animal population rabies increases the likelihood of equine contact with a rabid animal.

Many parts of the country have been impacted by the rabies threat for years; management of this concern has been by routine annual vaccination. It is fortunate that there are very effective and safe vaccines specifically labeled for horses to protect against rabies. Just as there are conscientious vaccination programs of cats and dogs, rabies immunization is now considered an equine core vaccine—highly recommended for annual administration—by the American Association of Equine Practitioners (AAEP).

Rabies is a disease that poses a danger to not just your horses, but also to you, your friends and family. 

Although livestock rabies is rare (only 15 horse/mule cases and 85 cattle cases were reported nationwide in the USA in 2015), the sobering reality is that it can have catastrophic consequences if it is your horse or your client's horse that becomes infected.

Clinical Signs

One significant problem is that rabies can look like just about anything else, not presenting solely as a neurologic disease. At first, an infected horse might not clean up its feed, or it might act a little “off,” possibly with a slight fever. As clinical signs become more obvious, the horse still might not appear neurologic, but rather an owner might complain that the horse has an inexplicable lameness or is acting colicky. 

Despite efforts by a veterinarian, the horse might not respond to treatment and instead continues to deteriorate. There are three possible progressions of rabies in an infected horse:

  1. The dumb form is when the horse is non-responsive to its environment, appears dazed or stuporous, and eventually becomes recumbent.
  2. The furious form is an aggressive animal that is extremely jumpy and hypersensitive to touch, sight or sound, and it is dangerous to be around. Some horses will begin to self-mutilate by biting at the itching, burning sensation around the original site of viral entry.
  3. The paralytic form occurs when a horse initially appears weak, is staggering, and becomes uncoordinated, perhaps dribbling urine similar to how a horse appears when affected with equine herpesvirus myeloencephalopathy (EHM). These clinical signs eventually progresses to total paralysis, recumbency and seizures. There is also hydrophobic behavior—when the thirsty horse is presented with water, spasms occur in the back of the throat, causing extreme agitation.

Disease Progression

There is no cure for rabies. It is 100 % fatal, usually within 4-5 days of development of clinical signs; but it can take up to 10 days for a horse to die. This means there is an unfortunately long period for people to become exposed, particularly early on when it is indeterminate that the horse is affected with rabies. 

Positive diagnosis in animals is only possible with post-mortem brain examination.

Most horse owners don’t readily think of horses as candidates for contracting rabies, but when you think about it, horses in pasture have unlimited opportunities to encounter wildlife. Think of all the times you’ve seen coyotes or foxes trot through your fields. In the barn, open or spilled feed containers or cat and dog food attract varmints, like raccoons and skunks. Once in proximity, they might circulate among stalled or paddock-confined horses. 

Wildlife accounts for 93 % of rabies cases each year, with raccoons leading the charge, followed by bats, skunks, foxes and other wild animals such as coyotes.

Incubation of the virus takes weeks to months, depending on the site of the bite. The difficulty lies in the fact that you aren’t likely to see your horse get bitten. And, there is often a protracted lag time between a bite and display of clinical signs, so you might not recall a previous, tiny wound. 

In a study of 21 cases, not a single bite wound was found on the animals positively identified as rabid.

This rapidly progressive and fatal Rhabdovirus disease begins with viral replication at the bite site, which then travels through the peripheral nerves to the spinal cord and brain, whereupon clinical signs begin to show. 

Once in the central nervous system, virus makes its way to the salivary glands and eye secretions. From these excretions, it then can be passed on to unsuspecting mammals, such as the inquisitive horse that ambles over to sniff the oddly behaving creature lurking in the pasture, which then bites the horse.

There is a huge impact on everyone when a rabid animal is identified; rabies prophylaxis is often necessary for exposed humans. A methodical track-back process takes place to notify every single person that might have come into contact with that animal.

Prevention

The important point is this: RABIES IS PREVENTABLE. 

For horses, the rabies vaccine is given after 4 months of age and boosted annually. The available vaccines are 100% effective and quite safe. As with any biologic immunization product, there is always a chance of a transient adverse reaction, like achy muscles or low-grade fever. But considering the zoonotic (transmitted from animals to humans) risk of a rabid horse infecting people, concerns about transient vaccine reactions are not reasons to forego immunizing horses. 

Remember that a vaccine reaction is most likely from the adjuvant (carrier) used to stimulate immunity of killed viral vaccines and not the rabies antigen itself. 

If one rabies product causes a reaction, then the next year try another product made by a different manufacturer and/or pre-medicate the horse with NSAIDs (phenylbutazone or flunixin) prior to immunizing.

We are fortunate in the United States because we have, through immunization programs, limited the exposure of people to this fatal virus by controlling it in the domestic pet population. In the rest of the world, 50,000 to 100,000 people die each year from rabies, mostly in Asia and Africa. The number of people in the USA dying of rabies each year numbers less than two or three. Yet, Americans are still exposed to rabies resulting in necessary post-exposure prophylactic injections that are coupled with anxiety, discomfort and expense.

Besides vaccinating your horses against rabies, other recommendations to minimize your horse’s risk of rabies exposure include:

  • Minimize wildlife contact in the barn by eliminating the availability of open feed attractants and using animal-proof garbage containers, and in pastures keep grass mowed to reduce areas where wildlife can burrow and hide.
  • Take note of even the smallest wound on your horse.
  • Beware of any animal that is acting strangely, especially normally nocturnal wildlife that is present in the daytime or wildlife that acts overly friendly. If you see such an animal, contact Animal Control to deal with the situation.
  • Teach your children and boarders to be cautious in touching or handling stray or dead animals, whether domestic or wildlife.

With some foresight and simple preventive strategies that include annual vaccination of all horses on your property, equine rabies is preventable.