Canine influenza outbreak caused by Asian virus, scientists say

The canine influenza outbreak afflicting more than 1,000 dogs in Chicago and other parts of the Midwest is caused by a different strain of the virus than was earlier assumed, scientists at Cornell University and the University of Wisconsin say in a Cornell media release.

Researchers at Cornell say their test results indicate that the outbreak is being caused by a virus closely related to Asian strains of influenza A H3N2, currently in wide circulation in southern Chinese and South Korean dog populations since being identified in 2006. There is no evidence that it can be transmitted to humans, they say.

The outbreak in the Midwest was previously thought to be a result of the H3N8 strain of virus, which was identified in the U.S. dog population in 2004 and has been circulating since, the release states. The H3N2 virus had not been previously detected in North America. The outbreak in Chicago suggests a recent introduction of the H3N2 virus from Asia.

Testing of clinical samples from the outbreak conducted at the New York State Animal Diagnostic Laboratory at Cornell indicated that the virus was influenza A. Further testing led researchers to believe a new strain was at fault. Subsequent testing, carried out with the assistance of the Wisconsin Veterinary Diagnostic Laboratory, identified the new subtype as H3N2. The National Veterinary Services Laboratories in Ames, Iowa, is sequencing two isolates from this outbreak to facilitate complete characterization of the viruses.

Both influenza strains can cause high fever, loss of appetite, coughing, nasal discharge and lethargy, researchers say. Symptoms may be more severe in cases caused by the H3N2 virus. Some infected dogs may not show symptoms at all.

H3N2 has caused infection and respiratory illness in cats, according to the Cornell release.

Researchers are advising veterinarians that samples from sick pets can be tested using a broadly targeted influenza A matrix reverse transciptase-polymerase chain reaction assay (Rt-PCR). The canine-specific influenza A H3N8 Rt-PCR in use in several laboratories will not detect this virus, they say. Serology is also currently not available, as the H3N2 virus is different enough from H3N8 that antibodies may not cross-react. However, an H3N2-specific serologic assay is under development and will be available soon, the release states.

Researchers do not know yet if the current canine influenza vaccine will provide any protection from this new virus. It does protect against H3N8, they say, which is in circulation in some areas. Other preventive advice remains the same: In areas where the viruses are active, pet owners need to avoid places where dogs congregate, such as dog parks and grooming salons.