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

International equine athletic events can create a lot of hassles from an infectious disease standpoint. Mixing animals from different areas creates a prime opportunity for transmitting infectious diseases between horses. An additional concern is when some horses might carrying infections that are considered "foreign" to horses from other areas.

During the 1996 Olympics in Atlanta, concerns about the potential for introduction of piroplasmosis (to the US) led to much angst, and restrictions such as only allowing horses carrying the disease to compete in indoor events. Piroplasmosis concerns have also played a role in planning the World Equestrian Games in Kentucky.

Piroplasmosis is caused by the bloodborne parasites Babesia caballi and Theileria equi, and is spread by ticks (as well as re-using needles and other modes of blood transmission). While it can be a fatal disease, some infected horses appear healthy, and these silent carriers can spread the disease to the ticks, which then spread it to other horses.

What to do regarding piroplasmosis was an important consideration for the World Equestrian Games. To even be awarded the games, a clear and fair plan was required to get approval from both the FEI and US Department of Agriculture. Balancing infectious disease risks with limited disruption of activities isn't easy, and it's not an exact science. Significant efforts have been taken to reduce the potential for piroplasmosis transmission. These include:

• Surveys of the park taken prior to the bid that showed minimal tick activity.
• Planning the event for late September and October because ticks are typically dormant by that time of the year (in Kentucky).
• Trapping small mammals at the park from 2006-2008 to study tick levels and types.

During the games:

• Known piroplasmosis carriers will be housed together in a separate barn that will be treated to eliminate ticks.
• Carriers will be inspected for ticks when they enter or leave the stable area.
• In advance of the event, all horses currently at the park have been inspected and treated for ticks.

You can never guarantee that an infectious disease won't slip through even the most strict measures, but that's the nature of infection control. This seems like a nice evidence-based, logical plan to reduce the risk of piroplasmosis dissemination during the Games.

Photo by Ronald Yochum, 2006 (click for source)

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The Royal Canadian Mounted Police's famed Musical Ride has been hit with strangles, and has canceled shows in Alberta and Saskatchewan. It's reported that only one horse is affected, but it's quite possible (if not likely) that others are also affected or will be soon, considering the highly transmissible nature of the disease. It can be contained with good infection control practices, particularly if caught early, and hopefully that's the case here.

Horses like these, that travel widely to shows and other events, are at high risk for exposure to microorganisms like Streptococcus equi, the cause of strangles. The more horses a horse encounters (particularly transient populations as are encountered at shows), and the fewer the infection control practices at shows, the greater the risk of disease.

More information about strangles can be found on the equIDblog Resources page.

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Last year, there was a large equine influenza outbreak at the Crawford County Fair in Pennsylvania. In response to that, a mandatory influenza vaccination policy was implemented. However, registrations for this year’s fair have dropped by 1/3 from 457 to 310. One horse owner says “It’s because of the shots.”

This is a pretty unfortunate response by horse owners. Mandatory vaccination is an entirely reasonable component of an infection control program that should be more widespread. Shows are optimal environments for transmission of disease. Huge numbers of horses get sick ever year from infections acquired at shows and outbreaks are not exactly rare.

One horse owner explains her decision not to show as “It’s the expense, plus there’s the risk of an adverse reaction to the shots.” That’s code for “It’s the expense.”

Vaccines are pretty cheap, especially when you consider how much money is spent on the horse and showing each year. People often spend huge amounts on boarding, (largely unnecessary) supplements, tack and other supplies, along with the costs of registering and traveling to shows. Concerns about adverse reactions are often used to justify non-vaccination, but it’s usually just an excuse. Adverse reactions to vaccines are quite rare and typically minor. Adverse reactions to intranasal influenza vaccination are extremely rare to non-existent.

Hopefully this fair sticks with this policy. They should be commended for taking a responsible action and more fairs should be doing the same thing. Personally, this is a fair that I’d want to show at. The vaccination requirement means there’s less chance of a horse acquiring influenza. Also, weeding out people who are too cheap or otherwise unwilling to use good preventive medicine strategies should decrease the pool of horses that are carrying other infectious diseases. Those people can organized their own vaccine-free show (the biohazard games).

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Because quarantine and testing are not 100%, good general infection control practices are also required. The presence of a quarantine must not create a false sense of security and thereby be used as an excuse to relax basic infection control practices. These include things like restricting direct and indirect contact (e.g. sharing buckets) between horses, good hand hygiene by people working with the horses, and close monitoring for signs of disease, among other things. The intense preparations that are involved here show the importance of infectious disease in the equine industry and an excellent awareness of the problem.

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