Vol. 22, No. 6, Sept. 19, 2002

UI lab confirms first cases of West Nile in canines, squirrels

Jim Barlow, Life Sciences Editor
(217) 333-5802; b-james3@illinois.edu


CHAMPAIGN, Ill. — 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 affected animals.

A dog, a wolf and three gray squirrels have died of West Nile infection, said John Andrews, a veterinarian and director of the Veterinary Diagnostic Laboratory in the College of Veterinary Medicine. 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.

"We’ve identified several interesting cases of concern over the last several weeks," Andrews said. "We have several cases of squirrels that had been showing clinical signs of the disease, and we have shown that West Nile had infected at least three of these squirrels and in fact is the cause of their clinical signs and their deaths."

The virus, common to Africa, the Middle East and West Asia, had been known to infect humans, birds, mosquitoes, horses and some other mammals. It was identified in the eastern United States in 1999. In humans, it may cause a flu-like illness that lasts a few days. However, the virus can be fatal for people with other diseases, if it progresses into encephalitis, a swelling of the brain. Illinois leads the nation in human cases of the virus.

Officials expect to find through tissue testing that several additional cases of squirrel deaths can be attributed to West Nile, Andrews said.

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 and the Illinois Department of Public Health.

The deaths of two squirrels in Chicago and one in Champaign, an 8-year-old dog (an Irish setter-golden retriever mix) in Bloomington-Normal, and a 3-month-old wolf from a small zoological collection in suburban Will County (southwest of Chicago) are positively linked to West Nile. The squirrels appeared to have been less than a year old, Andrews said.

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. In addition, the Veterinary Diagnostic Laboratory has confirmed losses statewide of raptors, owls and other wild birds, as well as pelicans and flamingos in Illinois zoos.

"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."

So far the only documented human-to-human spread of West Nile infection has occurred through transplanted organs. As of Monday (Sept. 16), there were 249 confirmed cases of horses in Illinois that had been infected by mosquitoes, but there have been no reports of human infection from the horses or of horse-to-horse infections, Andrews said.

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

"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.

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