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WEST NILE VIRUS IN LLAMAS AND ALPACAS:
What is the risk? What should we do?
David E Anderson, DVM, MS, DACVS
Professor, Large Animal Clinical Sciences
College of Veterinary Medicine, University of Tennessee
Knoxville, Tennessee
With the spread of West Nile Virus (WNV) throughout the USA, there has been an increased interest in the dangers associated with this disease. Along with the many confirmed cases of infections of birds and humans, there have been several dozen cases diagnosed in llamas and alpacas since the WNV entered the USA. Although many llamas and alpacas confirmed to be infected with the virus have died, many have survived with supportive treatments. In field studies, the prevalence of llamas and alpacas testing positive for exposure to WNV ranged from 15 to 50% in different herds. Fortunately, extremely few of these animals develop clinical signs. The WNV most commonly infects birds. Mosquitoes become infected when they feed on infected birds. Humans and other animals become infected when infected mosquitoes feed on them.
Clinical signs that might cause us to suspect WNV infection include apparent depression, lethargy, weakness, muscle tremors, decreased appetite, fever, staggering, recumbency, seizures, coma, and death. If these clinical signs are observed, consult a veterinarian as soon as possible for diagnosis and treatment. Early intervention by a veterinarian will improve the likelihood of survival and recovery.
The best prevention is through vaccination and environmental management. As with all vaccines utilized in the llama and alpaca industry, this would be considered extra label use. In research conducted at The Ohio State University and Oregon State University, llamas and alpacas responded to vaccines labeled for use in horses. The duration of antibody response varies from 3 to 6 months. If the animal had been vaccinated in previous years, a booster vaccine is recommended. Environmental management can greatly reduce risk by eliminating the density of mosquitoes in the area. Mosquitoes require stagnant water with relatively low oxygen content to lay eggs and facilitate survival of larvae. In general, mosquitoes will not lay eggs on turbulent waters. Stagnant water should be drained (runoff, puddles) or changed (e.g. water buckets) frequently. Water areas, such as ponds, that cannot be drained, can be made to be inhospitable to mosquitoes by adding ornamental fountains or sprinklers. These disrupt the water’s surface and increase oxygen content diminishing the propagation of mosquitoes. Mosquito treatment of water sources and environmental and personal mosquito repellants should be used cautiously and according to label directions.