Outbreak of canine influenza caused by new strain of virus

An outbreak of canine influenza in the Chicago area ongoing as of mid-April has been caused by a strain of virus not previously detected in North America, according to scientists at Cornell University and the University of Wisconsin-Madison.

The scientists say the outbreak has been caused by a virus closely related to Asian strains of influenza A H3N2 viruses, currently in wide circulation in Chinese and South Korean dog populations since being identified in 2006. The Chicago outbreak had been attributed to the H3N8 strain of virus, which was identified in the U.S. dog population in 2004 and has been circulating throughout the country since.

On April 15, the U.S. Department of Agriculture’s National Veterinary Services Laboratories completed sequencing an isolate from the Chicago outbreak, confirming that an Asian H3N2 virus has been circulating.

Both influenza strains can cause high fever, loss of appetite, coughing, nasal discharge, and lethargy. Signs of illness may be more severe in cases caused by the H3N2 virus. Some infected dogs may not show any signs of illness. H3N2 can cause infection and respiratory illness in cats, although there is no evidence that the virus can be transmitted to humans.

It is not known if the current vaccine for dogs against H3N8 will provide any protection against H3N2.

Diagnostic testing of samples from sick pets can be done with a broadly targeted influenza A matrix reverse transcriptase PCR assay. The canine-specific influenza A H3N8 RT-PCR assay in use in several laboratories will not detect H3N2. Serologic testing to detect H3N2 is available from Cornell.

Resources on canine influenza are available from the AVMA here.