New developments in Midwestern canine influenza outbreak

New laboratory tests show that a strain of canine influenza virus (CIV) associated with more than 1,000 sick dogs throughout the Midwest, including one dog in Madison, is virtually identical to an Asian strain of the virus and is not a mutated form.

A week ago, initial tests at the Wisconsin Veterinary Diagnostic Laboratory (WVDL) and Cornell University identified the strain as H3N2, which has previously only been seen in Asia and is different than the H3N8 strain circulating in North America. Genetic sequencing conducted at the National Veterinary Service Laboratory in Ames, Iowa, now confirms that the H3N2 strain found in the Midwest is almost identical to its Asian counterpart and was likely brought to the United States by an infected animal.

“This means there is no evidence of genetic reassortment,” says Kathy Toohey-Kurth, virology section head at WVDL. “This is good news because mutations are unpredictable, and we would not necessarily know what the safety implications are for humans or other animals.”

There is no evidence at this time that the H3N2 CIV strain can infect humans; it is distinctly different from human seasonal influenza H3N2 strains. However, the Asian H3N2 CIV strain has been reported to infect domestic cats.

“No cats have reported positive in the United States at this time,” says Keith Poulsen, WVDL diagnostic and case outreach coordinator and clinical assistant professor at the UW-Madison School of Veterinary Medicine (SVM). “Two cats and a dog, housemates of the infected dog in the Madison area, tested negative today despite showing clinical signs of the virus. It’s possible the tests were done too late to catch the viral shedding phase. Either way, it’s good news for those animals.”

Both CIV strains can cause persistent cough, runny nose, and fever. A small percentage of dogs will develop more severe clinical signs, and some will not show any symptoms at all. The infection has been associated with some deaths.

Neither CIV strain is related to the highly pathogenic H5N2 avian flu, which has been reported in Wisconsin this week; they are completely different strains that affect separate species.

The commercially available vaccines for CIV are made to protect against the H3N8 strain, and their effectiveness against the H3N2 strain is unknown at this time, but it is likely to be less effective.

“We’re still recommending that owners vaccinate their dogs because H3N8 is still around,” says Sandi Sawchuk, primary care veterinarian at UW Veterinary Care (UWVC) and SVM clinical instructor.

UWVC veterinarians also recommend taking the following measures to minimize risk to pets:

• Limit direct dog-to-dog contact. This is especially important with unknown dogs and any dogs displaying clinical signs, including cough, running nose, and fever. If your dog shows any of these signs, contact your veterinarian and do not take your dog to a boarding facility, dog daycare, dog park, or other public space.
• The virus will live in the environment for 24 to 48 hours in the majority of cases, but washing with soap and water is very effective at inactivating influenza virus.
• Wash your hands and change your clothes if you work with or are exposed to sick dogs before handling your own pets at home. This also applies to veterinarians in practice.

In addition to these recommendations, the WVDL has compiled information and sampling guidelines for veterinarians, and the SVM Shelter Medicine Program and Koret Shelter Medicine Program at the University of California, Davis, have compiled CIV resources for animal shelters.