While rare, dogs (and cats) can be bitten by mosquitoes and come down with West Nile Virus. From the Reno Gazette-Journal:
A treasured family dog that became suddenly ill and had to be put to sleep earlier this week was infected with the West Nile virus, the second rare case of canine infection reported in Washoe County, officials said Friday.Dogs are generally safe from West Nile, which is more likely to strike humans and horses, said a local veterinarian and officials from the Nevada Department of Agriculture. The virus is carried by birds and transmitted to humans and other animals by the bite of mosquitoes.
“It’s rare, but dogs can come down with it,” said Dr. Ron Anderson of the department’s Animal Disease Laboratory. “It’s certainly an infrequent happening.”
Last year, the federal Centers for Disease Control and Prevention reported fewer than 40 dogs and only one cat infected with West Nile virus nationwide.