If your vet is telling you dogs cannot and do not get WNV they are simply WRONG. If they are actually just stating that it would be a rarity that your dog contracts and shows any effect of the virus then they are correct. If they are emphatically stating that dogs are not able to contract or are affected by WNV, they need to brush up on their infectious disease information.
Below is the surveillance report from the CDC I noted above from 11/2003 that includes dogs. The number was 26 at that time. 2003 reports indicate that less than 40 dogs have been reported to have contracted notable WNV (much higher now). However, serological studies indicate that a relatively high number of dogs have actually been infected and just shown no signs of the disease as is the case with humans.
West Nile Virus Activity --- United States, November 6--12, 2003
This report summarizes West Nile virus (WNV) surveillance data reported to CDC through ArboNET as of 3 a.m., Mountain Standard Time, November 12, 2003.
During the reporting week of November 6--12, a total of 176 human cases of WNV infection were reported from 12 states (Arizona, Georgia, Kansas, Louisiana, Maryland, Nebraska, New Jersey, New Mexico, Pennsylvania, South Dakota, Tennessee, and Virginia), including two fatal cases from Louisiana. During the same period, WNV infections were reported in 39 dead birds, 12 mosquito pools, 93 horses, one cat, and five dogs.
In addition, 11,115 dead birds with WNV infection have been reported from 42 states, the District of Columbia, and New York City. WNV infections also have been reported from 41 states in horses (n = 4,084), dogs (n = 26), squirrels (n = 17), cats (n = one), and unidentified animal species (n = 31).
A related article from the CDC
West Nile Virus and Dogs and Cats
NEW!! *A recent article (Austgen et al. Experimental Infection of Cats and Dogs with West Nile Virus, EID, Vol. 10, no.1 Jan 2004) in the journal Emerging Infectious Diseases discusses WNV infection in dogs and cats in detail.
Q. Can West Nile virus (WNV) cause illness in dogs or cats?
A. A relatively small number of WNV infected dogs (<40) and only 1 WNV infected cat have been reported to CDC during 2003. Experimentally infected dogs* showed no symptoms after infection with WNV. Some infected cats exhibited mild, nonspecific symptoms during the first week after infection--for the most part only showing a slight fever and slight lethargy.
It is unlikely that most pet owners would notice any unusual symptoms or behavior in cats or dogs that become infected with WNV.
Q. How can my veterinarian treat my cat or dog if they are/may be infected with WNV?
A. There is no specific treatment for WNV infection. Full recovery from the infection is likely. Treatment would be supportive (managing symptoms, if present) and consistent with standard veterinary practices for animals infected with a viral agent.
Q. Does my dog/cat becoming infected pose a risk to the health of my family or other animals?
A. There is no documented evidence of dog or cat-to-person transmission of West Nile virus. The evidence suggests that dogs do not develop enough virus in their bloodstream to infect more mosquitoes. Cats develop slightly higher levels of virus in their bloodstream, but it is unclear if this would be enough to infect mosquitoes. It is very unlikely that cats would be important in furthering the spread of the virus. *
If your animal becomes infected with WNV, this suggests that there are infected mosquitoes in your area. You should take measures to prevent mosquitoes from biting you (use repellent and wear protective clothing.)
Veterinarians should take normal infection control precautions when caring for any animal (Including birds) suspected to have this or any viral infection.
Q. How do cats and dogs become infected with West Nile virus?
A. Dogs and cats become infected when bitten by an infected mosquito. There is also evidence that cats can become infected with the virus after eating experimentally infected mice. *