In a follow-up to a statement by the CDC late last week, the agency had the following to say about the new revelations concerning the dog flu outbreak in the Midwest:
A canine influenza A H3N2 virus is responsible for an outbreak of dog flu reported in the Chicago area according to a press release issued by Cornell University, home to the New York State Animal Diagnostic Laboratory. Dog flu is a contagious respiratory disease in dogs. Two canine influenza viruses have been identified worldwide: an influenza A H3N8 virus and an influenza A H3N2 virus. No human infections with either of these canine influenza viruses have ever been reported.
Previously, canine influenza A H3N8 viruses have been identified in U.S. dog populations. However, testing at the New York State Animal Diagnostic Laboratory and the Wisconsin Veterinary Diagnostic Laboratory suggests the dog flu virus responsible for the current outbreak in dogs is an H3N2 virus similar to Asian H3N2 dog flu viruses that have been detected in dogs in parts of Asia since 2007.
The National Veterinary Services Laboratories in Ames, IA is sequencing two isolates from this outbreak to facilitate rapid complete characterization of the viruses. A virus isolate also is being sent to the Centers for Disease Control and Prevention for additional analysis.
Signs of dog flu infection in dogs include cough, runny nose and fever, but not all dogs will show signs of illness. The severity of illness associated with dog flu in dogs can range from no signs to severe illness resulting in pneumonia and sometimes death in dogs. Tests are available to determine if a dog has been infected. CDC recommends that people concerned about dog flu in their pets speak to their veterinarian.
Almost all dogs can be susceptible to infection with canine influenza viruses, and illness tends to spread among dogs housed in kennels and shelters. A vaccine to protect dogs against canine influenza A H3N8 has been available in the United States since 2009. It is not known yet whether the H3N8 dog flu vaccine will offer protection against the H3N2 dog flu virus.
To date, there is no evidence of transmission of dog flu viruses from dogs to people and there have been no reported human infections with the canine influenza viruses. Animal studies suggest that neither virus transmits well to other companion animal species[308 KB, 10 pages] with the exception of H3N2 dog flu, which has been known to infect cats. CDC considers the human health risk posed by this dog flu outbreak to be low at this time. Once available, full genetic sequencing information on this virus will further inform the human health risk assessment. CDC will continue to watch this situation closely and provide updated information as it becomes available.
Two Dog Flu Viruses
Canine influenza A (H3N8) virus is closely related to an influenza virus found in horses for more than 40 years. Experts believe this horse influenza virus changed in a way that allowed it to infect dogs, and the first dog flu infections caused by these viruses were reported in 2004, initially in greyhounds. This virus is now considered a dog-specific lineage of influenza A (H3N8) virus.
In 2007, a canine influenza A H3N2 virus was detected in dogs in South Korea. This virus seems to have been an avian influenza virus that adapted to infect dogs. This canine H3N2 virus has since been reported in China and Thailand, and reportedly can affect cats as well as dogs. It is different from human seasonal H3N2 viruses.