The nation's first documented cases of domestic canine and squirrel deaths attributed to the West Nile virus have been confirmed at the University of Illinois at Urbana-Champaign. Officials stress, however, that people have a low risk of contracting the infection from infected animals.

The deaths of an 8-year-old dog (an Irish Setter-Golden Retriever mix) in Bloomington-Normal, a 3-month-old wolf from a small zoological collection in suburban Will County (southwest of Chicago), and three apparently young squirrels have been positively linked to West Nile virus, said Dr. John Andrews. Dr. Andrews is a veterinarian and director of the Veterinary Diagnostic Laboratory in the College of Veterinary Medicine. The university's work is being done by the Veterinary Diagnostic Laboratory and its related Zoo Pathology Program located in Chicago, in close cooperation with the Illinois Department of Natural Resources (DNR) and the Illinois Department of Public Health. The diagnoses were confirmed by the Illinois Department of Public Health laboratory in Chicago and by medical entomologist Robert Novak of the State Natural History Survey on the Illinois campus.

The wolf showed no signs of other diseases, but the dog and some of the squirrels had laboratory findings indicative of other potentially immune-compromising infections. The squirrels appeared to have been less than a year old.

Dog owners may want to limit the exposure of their animals to mosquitoes, especially any dogs already suffering from other diseases, Andrews said.

"At this point, we do not believe that squirrels develop significant levels of the virus in their bloodstream (a condition known as viremia)," he said. "If the animals don't develop a significant viremia, we do not believe that they are capable of shedding the virus either back to mosquitoes or to other creatures around them, including humans. The risk, we believe now, is very low but still under investigation."

"I think our squirrel population is going to take a hit. At this point in time, however, we don't see an unusual risk for the spread of the West Nile virus from squirrels or dogs to humans. We believe the highest risk to humans is from mosquitoes, but precautions should be taken around squirrels that might be acting funny and with dogs whose health may be compromised by other immune-related diseases."

Residents who find dead squirrels should dispose of them, Andrews advised. However, if they see a squirrel exhibiting nervous-disease-like behavior and then it dies, they should contact their local DNR office.

Comments from our Veterinary Staff:

This is the first substantiated case of West Nile virus infection in dogs in the United States. It should be emphasized that this dog appeared to have a weakened immune system. It has been shown that West Nile virus more commonly affects those humans who may have suppressed or weakened immune systems, such as the very young or the elderly.

Pet owners should not become overly alarmed, but they can take measures to protect their animals from exposure to mosquitoes. There are a number of flea and tick products for dogs and cats that act as mosquito repellents. Products with mosquito-repellent properties contain the ingredients pyrethrins or permethrins such as Defend, Bio Spot for Dogs, and many products for cats. These products need to be used with care, and permethrins should never be used on cats. For more information on flea and tick product ingredients and using these products, see Ingredients in Flea and Tick Products and Using Flea and Tick Products Together. To protect your pets, also limit the amount of time they spend outside, especially at those hours when mosquitoes are more abundant.

For more information on West Nile virus infections in humans and animals in the United States, see the article: Update on West Nile Virus, October 2002.