There are two different vaccines available for horses for the prevention of WNV-associated disease.
West Nile-Innovator™, the vaccine developed by Fort Dodge, was given a conditional license in August 2001, and was granted full licensure in February 2003. The manufacturer recommends 2 initial doses of this killed virus product, given intramuscularly, 3-6 weeks apart, and then annual booster vaccination. Protection from disease is reportedly achieved at least 6 weeks after the second initial vaccine dose. Over 13 million doses of the vaccine have been used nationwide, and the reported vaccine efficacy is 95 percent; in other words, 95 percent of properly vaccinated horses will be protected from disease if bitten by a mosquito carrying WNV.
The WNV vaccine is a killed, adjuvanted product similar to vaccines against EEE and WEE and is only available through licensed veterinarians. Horses vaccinated against EEE, WEE, and Venezuelan Equine Encephalitis are not protected against infection with WNV.
RecombiTEK™, developed by Merial, was released in January, 2004. This vaccine has been approved for veterinary use by the USDA. RecombiTEK™ contains recombinant canarypox vectored West Nile Virus vaccine that has been modified to express the desired antigens capable of stimulating a protective response to the West Nile Virus. Two initial doses, 4-6 weeks apart are recommended by the manufacturer, as well as a single annual booster.
West Nile-Innovator™ and RecombiTEK™ vaccines work in completely different ways and cannot be used interchangeably. Horses previously vaccinated with West Nile-Innovator™ would need to start their vaccination series over again with 2 initial doses if using the RecombiTEK™ vaccine this year. Horse owners are advised to consult their veterinarian concerning WNV vaccination of their horses. Vaccinated horses can be differentiated from infected horses on laboratory tests.
In addition to the vaccine for horses, simple insect control measures should be utilized. Consider the use of insect repellents, and place horses in barns/stables under fans during dusk, dawn, and other times when mosquitoes are present. Eliminate opportunities for mosquito breeding by draining wet areas of pasture; filling puddles; repairing eaves troughs, gutters, etc.; clearing any containers that might hold even small pools of water; and draining water tanks once or twice weekly. Additionally, consider control of mosquitoes in ponds and large water containers through the use of larvacides and fish.
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