Colorado State University veterinarians are recommending the use of equine West Nile Virus vaccines to help prevent West Nile Virus disease in alpacas. While llamas seem to be fairly resistant to developing severe disease signs, West Nile infection in alpacas sometimes results in life threatening neurological disease (encephalitis) just as is seen in horses and humans.
Signs in alpacas include lethargy, decreased appetite, weakness, muscle tremors, head and neck tremor, stumbling, incoordination, and in severe cases, paralysis leading to recumbency. About 10 percent of alpacas showing neurologic signs may die from the disease.
“The hot and dry weather across the country has created ideal conditions for the type of mosquitoes that transmit West Nile Virus,” said Dr. Rob Callan, head of Colorado State’s livestock veterinary service at the Veterinary Teaching Hospital.
“Transmission of the virus varies from year to year and depends on a number of factors, including mosquito numbers, but it is present again this year in Colorado livestock: Four equine cases of West Nile Virus have been diagnosed in horses from Fremont, Weld, and Montrose counties in Colorado so far this season.”
West Nile Virus is carried by infected birds and is spread locally by mosquitoes that bite infected birds. Bites from infected mosquitoes can then pass the virus to humans and animals.
While there are no West Nile Virus vaccines licensed for use in llamas and alpacas, equine vaccines provide protection that may prevent or decrease the severity of disease in these animals, Callan said.
Based on the limited data available, vaccination of alpacas against West Nile Virus is recommended between 4-16 months of age with a two-dose (Merial Recombitec) or three-dose (Fort Dodge Innovator) protocol followed by a single dose booster vaccination the second year. After that, producers can consider to either continue with annual vaccination, or to direct vaccination to only their most valuable animals.
“Based on the dramatic decrease in clinical cases in alpacas since West Nile Virus was introduced in the area, it appears that following initial vaccination and booster, alpacas will retain enough protection to minimize the development of neurological disease and be re-immunized by natural infection in following years,” Callan said. “Vaccination in llamas is considered optional since disease in llamas is so rare.”
Further West Nile Virus control is directed at reducing the mosquito populations and their possible breeding areas. Recommendations include removing stagnant water sources, keeping animals inside during mosquito feeding times – typically early morning and evening - and using mosquito repellents.
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