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Zoonotic Disease Update: Rabies and West Nile Virus

Friday, July 12, 2019  
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The season for rabies and West Nile Virus (WNV) is upon us! The most common sources of rabies in Arizona are bats, foxes, and skunks. When rabies activity increases within these animal groups, "spillover" into other mammal species occurs. As of June 15, 2019, a total of 66 animals have tested positive for rabies, including three domestic cats exposed to rabid skunks Cochise County (one cat in February) and Pima County (two cats in June). None of these cats were previously vaccinated for rabies; one had the gray fox rabies variant and two had the south central skunk rabies variant. Reports of domestic animal contact with wildlife should be reported to animal control or the Arizona Game and Fish Department.


As a reminder, veterinarians have the option to perform serologic monitoring in dogs or cats that have been exposed to a potential or known rabid animal if the dog or cat has previous rabies vaccine history but no documented proof. This would avoid the four-month quarantine or euthanasia by effectively reducing the quarantine to 45 days if a rise in titer level is documented following a vaccine booster (serum must be collected before the booster!). This should be communicated with the local animal control agency. More information can be found on page 11 here: Manual for Rabies Control & Animal Bite Management. To access Arizona rabies resources, such as regularly updated data on positive animals, access to Arizona’s rabies control and bite management manual, and more, visit: http://www.azdhs/rabies. WNV is primarily spread between mosquitoes and birds, but the virus can cause disease in people, horses, and other animals. Horses are susceptible to infection but an annual vaccine is available. Illness in dogs and cats is rare. Mosquitoes lay their eggs near water; therefore, it is encouraged to take steps to reduce areas of standing water around the home. Empty and scrub, toss or cover any items that can hold water, especially around livestock pens and keep yards clean and clear from debris. Larvicide can be placed in open nearby ditches and local vector control agencies can be contacted for other mosquito abatement activities.


As of June 8, 2019, there have been 218 WNV positive mosquito pools identified statewide, 216 of which are in Maricopa County. This is a lot higher than expected for this time of the year and we are expecting to see an increase in cases in humans (and potentially in horses (six human and one equine case reported as of June 14).


Many infectious and non-infectious causes can lead to neurologic signs in horses, however, especially for an unvaccinated animal, WNV (and rabies) could be considered on the differential when other causes are ruled out. Most WNV clinically affected horses exhibit anorexia, depression, and fever along with neurological signs such as ataxia, circling, hind limb weakness, recumbence, paralysis, altered mental state, impaired vision, lip droop, muscle fasciculation, dysphagia, or hyper-excitability.


To report a suspected case of rabies or WNV in horses with neurologic signs, contact the Arizona Department of Agriculture, State Veterinarian’s Office (602-542-4293). To learn more about West Nile Virus in Arizona and how to keep people, pets, and livestock safe, visit: http://www.azdhs/mosquito.