Economy: Spell It EEEBy Kentucky Equine Research Staff · February 1, 2011
Michigan had one case of Eastern equine encephalomyelitis (EEE) in 2008 and no cases in 2009. In 2010, 133 cases were reported, of which 55 were confirmed. According to Steve Halstead, state veterinarian for Michigan, the sagging economy may be partly to blame. Quoted in an article in Equine 360, a veterinary e-newsletter, Halstead explained that some horse owners might have neglected to have their animals vaccinated against EEE because of the cost of having a veterinarian administer the vaccine. While this is not the only explanation for the increased number of cases, it is at least one possibility.
Outbreaks of EEE can occur on a cyclic basis related to mosquito and bird populations in an area. Birds are a reservoir for the disease, according to Halstead. Birds that are exposed to the disease develop a level of immunity, leading to a drop in new infections. As those birds die and are replaced by their offspring and also by migrant birds that are not immune, cases pick up again. Mosquitoes are vectors, spreading the disease from birds to other animals. When mosquito numbers increase during a rainy season or in an area with standing water, disease outbreaks are more common. In addition, cases usually increase in the summer and fall as standing water pools dry up and mosquitoes are forced to expand their range. There is some speculation that their feeding habits change later in the year, making them more likely to feed on animals other than birds.
It is theorized that Michigan's steep rise in EEE cases resulted from the combination of high numbers of mosquitoes, a susceptible bird population, and hard economic times in which some horse owners could not afford to have their horses vaccinated against EEE.
Owners are encouraged to continue with EEE vaccinations in hopes of avoiding another year of high infection rates. If owners are able to afford only a limited number of vaccinations for their horses, Halstead suggested that they can check with their veterinarians as to which vaccinations could be delayed and which are extremely important at this time. For instance, in some areas of Michigan, vaccinations for Potomac Horse Fever could wait a while, but horses should stay current on protection from EEE and West Nile virus. The American Association of Equine Practitioners recommends EEE vaccination as a core vaccine for all horses.
In an effort to keep costs low, some veterinary clinics have set up vaccination days where owners can bring horses to the clinic on a particular date. Owners can also contact friends to bring neighborhood horses to one location so that a visiting veterinarian can vaccinate a number of horses at one time, spreading the cost of a farm visit among many owners.
