Recently, cases of a virus that had never been recorded in the US afflicted over 1,000 dogs in Chicago, and killed 5 of them (0.5% mortality rate). About 5-10% become severely ill. The strain, influenza A H3N2, had been making dogs sick in Hong Kong and southern China since 2006, but nobody knows how it got to the United States.
There is a vaccine available for a different strain of canine flu (H3N8), but veterinary professionals in the area aren’t convinced that the vaccine would offer enough protection against the new strain. Since canine influenzas aren’t especially common, most dogs don’t have any immunity to them. This Asian strain may be more transmissible than the old strain, and doesn’t cause symptoms (but is easily spread from) in about 20-25% of affected dogs. The symptoms that the rest of the infected dogs usually get include coughing, lethargy, lack of appetite, fever, nasal discharge, and labored breathing.
Unlike the H3N8 strain, H3N2 is can also infect cats and cause similar symptoms. Although it hasn’t done so in Chicago, it has made a lot of cats sick in Hong Kong and in China. The canine flu doesn't pose any known risk to humans, but Chicago veterinarians are recommending that dog owners reduce their dogs' contact with other dogs and get vaccinated for H3N8 if they aren't already.