Canine Influenza H3N2 Asian Strain

Dr. Ernie Ward

The recent canine influenza outbreak that apparently spread from the Midwest to at least 12 states has been identified as a new viral strain from Asia. Veterinary researchers from Cornell University and the University of Wisconsin Veterinary Diagnostic Laboratory have determined a canine respiratory virus found in China and South Korea, H3N2, is to blame for nearly 2,000 reported cases in the U.S. H3N2 is not known to be contagious to humans, although cats may be at risk for contracting the respiratory infection. This is the first time the Asian virus has been identified in the U.S.  

Here's a H3N2 prevalence map from June 2015 published by Cornell University

The current canine influenza outbreak was originally thought to be the result of H3N8 or canine influenza virus (CIV), a highly contagious canine respiratory virus first observed in Florida racing greyhounds in 2004. The more recent Asian strain, H3N2, was initially identified in 2006 in Asia. H3N2 originated in avian species and apparently mutated to become infectious to dogs, cats, and ferrets. Since 2006, H3N2 has been identified throughout China and South Korea.

There are two new vaccines for H3N2, produced by Zoetis and Merck, in addition to the vaccine for H3N8 canine influenza. There is no evidence the existing H3N8 vaccine will provide protection for the new H3N2 strain or vice versa.

Clinical signs associated with H3N2 canine influenza are similar to CIV: High fever, loss of appetite, coughing, nasal discharge, and lethargy. Infected cats experience similar symptoms. There is a rapid, specific viral test available for H3N2 canine influenza. Based on similar viruses, the incubation period is probably 2 to 3 days, clinical signs last 5 to 7 days, and an infected animal may be contagious for up to 21 days after clinical signs develop.

Coughing and upper respiratory signs are common with H3N2

We don’t know how this new strain of canine influenza arrived in the U.S. It is suspected that a dog harboring the virus was imported, although this has yet to be confirmed. Because this is a relatively new infection, we don’t fully understand the transmission and pathogenicity of H3N2 canine influenza virus.

If your dog displays any symptoms of respiratory illness, notify your veterinarian at once. H3N2 is highly contagious; avoid contact with other dogs if your dog becomes ill. When CIV first presented in 2004-05, U.S. veterinarians took great efforts to quarantine any dogs with fevers, coughing, and nasal discharge from other pets. These aggressive medical countermeasures helped prevent a widespread epidemic. It is important to notify your veterinarian about any respiratory symptoms before taking your pet to the clinic. Your pet will be immediately escorted to a separate clinic area and handled with proper infectious disease protocols to help prevent further spread.  

If you live in an area identified with a CIV or H3N2 outbreak, minimize contact with other dogs. Dog parks, lakes or beaches, kennels, and doggie daycare services need to be carefully supervised if you choose to take your canine. In outbreak areas, it is advised to vaccinate against both CIV (H3N8) and H3N2 viruses. There is no vaccine for cats for CIV or H3N2 at this time.

H3N2 Asian canine influenza appears to be more easily spread and may be shed for a longer period than CIV, up to 3 weeks or more. This may explain how quickly and widespread the Asian H3N2 outbreak has been in the U.S. The fact that cats can also contract and potentially spread the virus makes it even more worrying. Be exceptionally cautious if your dog or cat develops a fever, coughing, or nasal discharge.

Here are five keys to help prevent the spread of H3N2 influenza:

1.     Vaccinate dogs when appropriate against both CIV (H3N8) and H3N2. If you live in area or are travelling to a region with a known CIV or H3N2 outbreak, consider vaccinating your dogs immediately. If you do not know if CIV or H3N2 is in your area, contact your veterinarian.

2.     Limit dog-to-dog direct contact, especially nose-to-mouth contact.

3.     Basic washing and bathing with soap and water seem effective at inactivating the virus.

4.     H3N2 virus appears to survive in the environment for 24 to 48 hours. Avoid areas with known exposure to H3N2 for at least two days. Infected dogs should be quarantined for at least 21 days.

5.     If you handle a sick dog or cat, wash your hands and change clothes before contacting other animals.

The good news is that H3N2 appears to have a low mortality rate. Few dog deaths have been attributed to this new canine influenza virus. Because we still don’t have a complete understanding of the H3N2 virus, it’s imperative to keep in mind that both CIV and H3N2 may lead to life-threatening pneumonia or serious respiratory illness. In older pets or those with underlying disease, even moderate respiratory disease can be fatal.  

H3N2 is a significant animal influenza virus that must be closely monitored by all pet owners. There continue to be critical scientific and medical questions we don’t have answers for yet. Viruses can mutate quickly and recommendations change dramatically in little time. Take precautions with other dogs, wash your hands and bathe your dog frequently, and contact your veterinarian immediately if your pet develops any signs of respiratory illness.