Equid Blog : Horse Health & Diseases : University of Guelph : Ontario Veterinary College : Equine Infectious Diseases

A rabid horse has been identified in Bandera County, Texas - this is the first case of rabies in a Texas horse in almost 40 years. The horse started acting strangely, erratically and at times violently. Rabies was eventually diagnosed (diagnosis involves testing the brain after the horse dies or is euthanized) and the owners are undergoing post-exposure treatment.

Rabies is a rare disease in horses, but there is always a risk of exposure in regions where rabies is present in wildlife. The fact that equine rabies is rare is a good thing, but it can also breed complacency and lead to decreased vaccination rates.

Decreasing vaccination is a bad thing. Vaccination is cheap insurance for a very serious disease. Rabies is invariably fatal in horses. It's also a risk to anyone around the horse. Transmission of rabies from horses to people is theoretically possible through bites or other contacts that result in introduction of saliva into wounds, cuts or possibly the mouth, nose or eyes. I'm not aware of any documented cases of equine-to-human transmission of rabies, but given the severity of rabies, we need to be careful. Additionally, rabid horses have killed people because they can be unpredictable and aggressive. Based on all these factors, it's important that we not become complacent about rabies in horses, and a key component of rabies control is vaccination. However, vaccination is not the only aspect of rabies control. Using various management practices to reduce the risk of wildlife exposure and controlling rabies in wildlife in the area are other important measures, but individual horse owners can have the greatest impact on their horses' health by ensuring they are properly vaccinated against rabies.

If you own a horse, make sure it's vaccinated against rabies unless you live in a rabies-free region.  More information about rabies in horses is available on the equIDblog Resources page.

Image source: www.bbc.co.uk

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I received newsletter today from Intervet (a pharmaceutical company) that is targeted at equine veterinarians. One article discussed rabies in horses. It wasn't bad overall, but I thought the section on what to do when a horse might have been exposed to rabies was worth discussing.

The article asks, "If your client suspects that a horse has been bitten by a rabies-infected animal, what should be done?"

Answer: "Contacting you as the veterinarian is always the first step."

Great first step.  A second step that wasn't mentioned should be, "Try to identify and (safely) capture the animal that bit the horse." This is often impossible but certainly worthwhile if it can be done.  However, if you're trying to catch the offending animal, make sure you don't put yourself at risk of exposure to rabies in the process.  If the animal can be caught, it's rabies status at the time of the bite can be determined (either through testing or quarantine). If it can be shown that the animal wasn't rabid, a lot of stress, hassle and expense can be saved.

"If the horse was previously vaccinated... Then isolate and observe the animal for 45 to 90 days (your clinical evaluation will involve gait analysis, radiography and a spinal tap)."

Boosting the rabies vaccine is also a good idea. The next step, however, needs to be contacting local regulatory officials to find out what you have to do. They determine if, how and how long an animal needs to be quarantined - this is NOT the decision of the local veterinarian nor the animal's owner. Most likely, they will recommend a 45 day quarantine for a vaccinated horse, since this is what is recommended in the NASPHV Compendium on Rabies. The discussion of diagnostic testing makes no sense. There is absolutely no indication to perform diagnostic tests on a horse that has been bitten by a rabies suspect. None. There are no tests that can be used to diagnose rabies in live horses (also exposed horses don't instantly develop signs of rabies). Horses should be monitored closely for signs of rabies during the quarantine period, but that's it.

"...and have the client make a list of all people who had contact with the horse."

This is often done when horses have or are suspected of having rabies, but not horses that are potentially exposed. It is done to help public health personnel contact people that may have been exposed to rabies. A horse that was just bitten by an animal is not a risk for transmission of rabies.  (However, keeping a list of people who have contact with the horse after it's been bitten (i.e. durng the quarantine period) - which should be as short a list as possible - is a reasonable precaution in the unlikely event that the horse does develop rabies.)

"If the animal was not vaccinated, your options are to euthanize and perform a postmortem examination of the brain (the only way to definitely confirm rabies)..."

Euthanasia is one of the options that needs to be considered in an unvaccinated horse that has been exposed, which is one of the reasons that identifying the biting animal and testing it is critical, if it can be done. The last part of the above sentence (from the atricle) is complete nonsense. Why would you test the brain of a normal horse that has been euthanized because it's just been bitten by a potentially rabid animal? The horse isn't being euthanized because it has rabies, it's being euthanized because of the likelihood  of it developing rabies weeks to months later. Testing of the brain will tell you absolutely nothing if the animal was only bitten recently.

"...or isolate and observe the horse for six months and develop the human contact list."

Again, this needs to be decided based on discussions with regulatory personnel who are responsible for dictating what is to be done. A six-month quarantine is a pretty standard recommendation for an unvaccinated animal. Creating a human contact list should not be necessary, since quarantine involves severely restricting contact of people with the horse and only a few (ideally one) person would have any type of contact.

The article wraps up with the very true emphasis on vaccinating horses. It's a cheap measure to prevent a relatively rare but invariably fatal disease.

Click image for source.

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As a vet, I've been bitten by a wide range of animal species. When people talk about animal bites, they usually think about dogs and cats. Horses can (and do) bite as well. Most horse bites are probably playful nips that hurt a little yet don't cause major problems, but some bites can cause serious injuries and infections can result.

A recent paper in the Journal of Agromedicine (Langley and Morris 2009), with the rather unwieldy title of "That Horse Bit Me: Zoonotic Infections of Equines to Consider after Exposure Through the Bite or the Oral/Nasal Secretions". Bites apparently account for 3-4.5% of the approximately 100 000 annual emergency room visits in the US that are associated with horses. The authors of the paper review infections associated with bites and contact with organisms in the mouth and nose of horses.

A large number of bacteria have been associated with horse bite infections in people, including Actinobacillus, Streptococcus, Psuedomonas and Staphylococcus species. Some viruses can theoretically be transmitted by bites, but there's little evidence that this actually happens.

Although viruses are not of as much of a concern overall, rabies needs to be considered in every bite from a mammal. We pay a lot of attention to rabies with dogs, cats and wildlife, but it often gets ignored with horses. While I'm not aware of any reports of rabies transmission from horses to humans by a bite, it could happen.  Fortunately, rabies is rare in horses so the likelihood of exposure from this species is very low. However signs of rabies aren't always obvious initially, and rabies in horses may mimic other diseases. Sometimes, rabies looks like colic, and human exposure through bites or other contact is possible when handling, evaluating and treating affected horses.

Unlike with dogs and cats, there are no clearly defined protocols for dealing with bites from horses. Any dog or cat that bites a person is supposed to be quarantined for 10 days. The reason for this is if the animal is rabid and the disease is advanced enough for the animal to be capable of spreading rabies virus, it would invariably develop signs of rabies and die within this time period. We don't have similar guidelines for horses. I suspect the 10 day observation period would be adequate but we don't have good data. The paper states that in Kentucky, a 14 day observation period has been used by the state Department of Public Health.

At the conclusion of the paper, the authors make a few important general recommendations for reducing the risk of disease transmission from bites and oral or nasal secretions of horses:

• Use good general hygiene, especially hand hygiene, after any contact with horses.
• Use gloves and gown or lab coat when examining horses in a veterinary clinic or hospital. (This might be overkill for all horses. We don't require gloves for every horse contact, just contact with mucous membranes (e.g. mouth, nose), wounds, incision sites and other high-risk areas. I think bare hands are fine for general contact as long as there is good attention to handwashing after.)
• Consider mask and goggles if the horse is coughing or sneezing.
• Develop standard operating procedures for handling sick horses.
• Use isolation when needed.

I'd add a few more points:

• Avoid bites. Pay attention to what you are doing around horses to reduce the risk of being bitten. Do not encourage playful behaviours (e.g. nipping) that could lead to bites.
• If you are bitten and it breaks the skin, clean the site thoroughly with soap and water. If there is significant trauma, or if the bite is over a joint, hand, foot, or a prosthetic device, you should see a doctor immediately because antibiotics are most likely indicated. If you have a weakened immune system, you should be evaluated by a doctor after any bite.
• Avoid contact with the horse's mouth or nose if you have skin lesions. Cuts and scrapes can allow bacteria to enter your body and cause infections. If you have a cut on your hand, make sure it is covered with a glove or waterproof dressing if you are going to have contact with the horse's mouth or something that came from its mouth (e.g. a bit).

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A horse in Harford county Maryland has been euthanized because of rabies. The horse first starting showing signs of disease in mid-July, which manifested as "striking changes in behaviour." The report doesn't say when the horse died, but animals typically die within a few days of the onset of neurological disease. The horse was transferred to the New Bolton Center where rabies was diagnosed. Subsequent testing showed it was a raccoon rabies strain, although that does not mean that a raccoon was the actual source of infection.

Public health officials implemented a 45 day quarantine of the farm. Stray cats (about 25) were caught and euthanized. Fortunately, the family pets were properly vaccinated and have received booster shots (plus presumably a period of observation at home... a much better situation than if they were not vaccinated).

People that had contact with the horse have received rabies post-exposure treatment. This includes one person who had to be tracked down overseas.

Harford County Health Department spokesperson Bill Wiseman said "There was never a risk to public safety. This incident was a great example of public health work in action and cooperation between local, state and in this case, international authorities." I don't buy the statement that there was no risk to public health. While the risk of rabies transmission from infected horses is very low, it's not zero. Rabid horses have killed people because of their abnormal and sometimes aggressive behaviour. Further, the fact that this horse had rabies means that it got it from something. Rabies can have a long incubation period so it's not guaranteed that it acquired it on the farm, but you have to be prudent and assume that there is infected wildlife in the area that could pose a risk for other animals or people. Public health authorities managed the situation well and reduced the public health risks, but there were certainly still risks.

Rabies vaccination is highly effective. There is no statement about whether this horse was adequately vaccinated but it's unlikely. Proper vaccination would likely have prevented this horse's death, as well as the death of the stray animals, cost of vaccination of people, cost of veterinary care for this horse, quarantine of the farm and the associated financial and emotional costs. A dose of vaccine that costs a few dollars could have saved thousands of dollars and emotional stress.

Rabies is a rare disease in horses but its severity means it should not be ingored. Vaccinate your horses.

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A recent case of rabies in a horse in Kentucky should serve as a reminder of the importance of vaccination against this disease. The affected horse was a Thoroughbred that was presented to a referral clinic for signs of severe colic. After surgery, the horse began showing signs of neurological disease, developed violent seizures and was euthanized. This type of presentation is not unusual, as rabid horses often start out looking like they have other problems such as colic. The scenario of taking a horse to surgery due to signs of severe colic and finding out later that it actually had rabies is nothing new. A major concern with the non-specific nature of the early signs of rabies in horses is that a large number of people may be exposed to the horse before rabies is even considered.

Rabies is always fatal in horses. Transmission of rabies from horses to humans is extremely rare, but is a potential concern. Rabid horses can also be very dangerous due to their unpredictable and sometimes very violent behavior, and rabid horses have killed people. At the same time, rabies vaccination is cheap and very effective.  All horses should be vaccinated against this devastating disease.

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This post originally appeared on the Worm & Germs Blog site on December 12, 2008.

In 2008, the American Association of Equine Practitioners (AAEP) published updated vaccination guidelines for horses.  One of the changes from the previous set of guidelines was the inclusion of rabies as a core vaccine (meaning every horse should receive it).  There was lots of discussion about this at the recent AAEP Annual Convention in San Diego, CA.

Some veterinarians don't like the idea of vaccinating every horse against rabies.  Just like veterinarians and owners of dogs and cats who are concerned about over-vaccination in these species, the same concerns exist in equine medicine.  Equine rabies vaccines are not approved for use every three years like some canine and feline vaccines, so they still need to be given every year until someone can determine for how long a vaccinated horse is protected from infection.   Furthermore, there has never been (to my knowledge) a case of human rabies due to transmission from a horse.  These are all valid points, but there are also a lot of reasons why including rabies as a core vaccine for horses is very good idea:

• Rabies is a very deadly disease, in both animals and people.  To some owners, their horse is every bit a part of their family as any dog or cat could be.  To other owners, their horses represent a great investment, and part of their livelihood.  Even if the risk of disease in horses is low, protecting them is safe and easy, so it just makes sense.  As the saying goes, an ounce of prevention is worth a pound of cure, but when there is no cure and prevention is so simple... you do the math.
• Rabies vaccination is extremely effective in horses, producing an excellent immune response even with a single dose.  It does not require complex adjuvants that some other vaccines need to stimulate the immune system, which also makes it less likely to cause an abnormal vaccine reaction.
• Rabies is not a seasonal disease like many of the respiratory viruses or insect-borne diseases (e.g. West Nile) for which horses are also typically vaccinated.  Rabies boosters only need to be given once a year, so this can be done during a time of year when no other vaccines are required, if there are concerns about giving too many vaccines at once.
• Horses live outside and in barns.  Most are far less supervised than dogs and cats, but even these animals are at risk of rabies exposure.  A rabid animal could easily be "brave" enough to attack a horse, even though it normally wouldn't.  Bats can also easily get into and out of many barns - you may never know one was there, and finding a bite mark from a bat on a horse would be like looking for a needle in a haystack, but that's all it takes to transmit the virus.  So it makes sense to give your horse added protection by vaccinating it.
  
• Rabies in horses may not look like rabies at first.  One of the most common early signs is actually colic.  A rabid horse that looks like a colic may expose the people who are trying to look after it before they realize what the horse has.  In other horses the signs may be recognized too late, like the rabid horse that was found at the Missouri State Fair earlier this year, that resulted in exposure of many people.
• While rabies transmission from horses to people has not been documented, rabid horses have killed people, particularly horses that develop the "furious" form of rabies, which can cause them to become very violent.

For more information on rabies, see our rabies archive or the information sheet available on the equIDblog Resources page.

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In some areas, vaccines are readily available from multiple sources, including the internet. Some people like to purchase vaccines and administer them to their horses themselves in order to save money. But are the savings really worth the risk? Here are some things to consider:

• Your veterinarian obtains vaccines through a reputable distribution system, which ensures quality control, tracking of products, and proper shipping and storage conditions. When you buy vaccines from other sources(especially the internet), you don't have that same level of assurance. Vaccines that have been improperly handled may not be effective.
• Some sources of vaccines and drugs are of questionable quality - in these cases you can't always be sure that you are even getting what you think you ordered. Ineffective vaccines or contaminated products are a concern. It's not saving you money if the vaccine doesn't work!
  
• While uncommon, vaccine reactions do occur. If your horse has an anaphylactic (severe allergic) reaction after being vaccinated, the reaction usually happens right away.  The horse's chances of survival are much greater if your veterinarian is there, because the needed expertise, drugs and equipment are readily available. If you administered the vaccine yourself, your horse may die by the time a veterinarian arrives.
• If your horse develops any problems associated with a vaccine administered by your veterinarian, the manufacturer may get involved and assist with the problem. This will NOT happen if you buy the vaccine from another source and give it yourself.
• Rabies vaccines MUST be given by a veterinarian. (In some areas it's illegal for a non-veterinarian to even possess rabies vaccine.)  A horse that has received a rabies vaccine from a non-veterinarian is considered unvaccinated by public health authorities.  If an unvaccinated animal is exposed to rabies, the repercussions may be much more severe, and may even include euthanasia.
• Vaccination is just one part of your horse’s "wellness program". Some of the pressure for people to vaccinate their own pets is a failure of the veterinary profession to adequately emphasize the importance of preventive medicine, of which vaccines are just one component. Simply charging an owner for "annual vaccines" leads people to want to vaccinate their pets themselves because they can get the vaccines for much less money. Veterinarians need to emphasize that what they are charging for (and what is the most important component of the preventative medicine program) is an annual physical examination and health consultation, and that only a small portion of the fee is for the vaccines.

Vaccination is a minor component of your horse's preventive medicine program. A careful physical examination and consultation about potential, developing and ongoing health issues are the most important parts of this program. Even if you vaccinate your horse yourself (which is still not recommended for the reasons above), it is still critical that your horse has an annual examination.  It's better for your horse's health, and it can be easier and cheaper in the long run because problems can be detected and treated early.

This equIDblog entry was originally posted (in modified format) on the Worms & Germs blog on 16-Oct-08.

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Click on any of the highlighted links below for more information about these horse-related infectious disease topics. Topics that are not highlighted are in development and coming soon. New information will be added as it becomes available, so be sure to check this page regularly for the latest updates.

All information sheets found on this page can be freely downloaded, printed and distributed. The authors only request that this website (www.equIDblog.com) is acknowledged as the source.  The downloadable files on this page can be opened with Adobe® Reader®.  To get the latest version of Adobe® Reader® for free, click here.

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