Reducing the Risk of Dog Flu


When more than 1,000 dogs became sick with the highly contagious canine influenza H3N2 virus this past April in Chicago, the American Kennel Club (AKC) issued an advisory encouraging judges to ask exhibitors to open the mouths of their dogs when showing the bite during the oral examination. Calls from the fancy prompted the notice.

A logical scenario sparked worry. Opening a dog’s mouth for the oral exam, a judge potentially could touch an infected dog, not showing signs or mildly affected, and unknowingly spread the virus to other dogs in the lineup.

In reality, the advisory reiterated the AKC’s existing policy. “These have been our guidelines for years,” says Tim Thomas, director of dog show judges for the AKC. “If judges find it necessary to conduct the oral exam, which is their prerogative, we advise them to sanitize their hands after examining each dog.”

No dog show was ever linked to the initial spread of the H3N2 virus in the U.S. Having mutated from birds to dogs, the H3N2 avian flu virus had infected dogs in Asia since 2007. Although speculation about the origin of the new strain of flu was never confirmed, experts believed that H3N2 may have arrived in Chicago via infected dogs brought from China and Korea by well-meaning rescue groups. 

“The canine H3N2 flu was a brand new strain of flu that crossed from birds to dogs, and then could migrate with the movement of dogs from Asia to the U.S.,” says Jason Stull, VMD, PhD, DACVPM, assistant professor of preventive medicine at The Ohio State University. “This type of disease movement has happened before, most notably when Hurricane Katrina dogs that had heartworm and various other infectious diseases were relocated to places where those diseases, and related prevention methods, were very rare. This movement may have increased the disease risk in those new locations.”

Becky Schlikerman with the Cook County (Illinois) Department of Animal and Rabies Control says ultimately about 1,800 dogs were reported by local veterinarians to have been infected by the H3N2 virus and 11 dogs were believed to have died. No formal tracking system exists for veterinary diseases so exact numbers are not known.

Learnings from this year’s dog flu will help guide future preventive efforts. “Owner education is so important,” Schlikerman says. “Owners need to know to avoid areas where lots of dogs gather. Places like dog parks and doggy daycare are best to avoid, as well as using a dog walker who takes out several dogs.”  

Edward J. Dubovi, PhD, professor of virology at Cornell University College of Veterinary Medicine, whose laboratory analyzed many of the Chicago flu samples, says he was surprised at how fast the flu spread. “This outbreak went into full force around the Easter holiday when a number of people probably put their dogs in kennels,” he says. “You had a higher collection of dogs in smaller environments, giving the virus an opportunity to expand very rapidly.”

Although Chicago was hit the hardest, a second peak of H3N2 influenza virus occurred in Atlanta in mid-June, with later reports of cases in Los Angeles and the East Coast. The transmission process is much like flu in people. A sick dog transmits the virus to another dog through saliva, coughing and sneezing, contaminated objects such as food and water bowls, toys, collars, and leashes, and by people moving between infected and uninfected dogs.

Assessing the Risk of Dog Flu

The risk of dogs developing canine flu is impacted by many variables, such as the age, health status, preventive care, immunity, and frequency of dog-to-dog and dog-to-environment interactions. To learn more, the AKC Canine Health Foundation is funding a two-year study to redefine ways to prevent infectious diseases in group settings.

“The goal is to assess disease risk for dogs in group settings to better manage disease, bearing in mind that risk is not uniform,” says

Dr. Stull, who leads the study. “No two dogs are the same. In general, younger dogs are at greater risk to spread and acquire disease than dogs over several years of age that have been exposed to many diseases. Nonetheless, a perfect storm exists for the spread of infectious diseases in canine group settings.”

The Chicago H3N2 dog flu is probably the most well-known infectious disease outbreak, but there have been at least 20 others caused by 14 different pathogens since 1970. Among them are parvovirus, brucellosis, coronavirus, and parainfluenza. All occurred in canine group settings such as kennels and boarding and training facilities.

An earlier canine influenza virus, H3N8, was identified in 2004 in a racing Greyhound community in Jacksonville, Florida. Another outbreak occurred in the fall of 2003, though it is not known when and where the first dogs became infected. Similar to the H3N2 virus that mutated from birds, the H3N8 virus transferred from horses to dogs. Eight of 23 Greyhounds in the outbreak identified as canine influenza virus died from severe pneumonia. The H3N8 infections continued in Greyhound tracks across the country from 2004 to 2006. Thousands of dogs in at least 38 states were affected.

A canine influenza virus vaccine was developed in 2008. Considered a lifestyle vaccine well-suited for at-risk dogs that also receive the parainfluenza vaccine to prevent kennel cough, the H3N8 vaccine reduces illness in dogs that become infected and reduces the likeliness of the virus spreading to other dogs by shortening the shedding interval and the amount of virus shed. It is not known whether the H3N8 vaccine protects against the H3N2 virus that occurred in Chicago.

Dogs are particularly susceptible to the H3N2 virus because it is a novel virus in which they have no historic immunity. Ranging from mild to severe, H3N2 flu starts as an upper-respiratory illness depicted by a persistent cough, clear nasal discharge and low-grade fever combined with lethargy and reduced appetite. Although there is no treatment for the viral flu, dogs can receive supportive care to boost immunity. H3N2 is not zoonotic, meaning dogs cannot transmit it to humans, though it can affect cats.

The clinical signs of H3N2 influenza virus are similar to tracheobronchitis, or kennel cough, which can make it challenging for veterinarians to diagnose. Blood testing and nasal and throat swabs are used to confirm diagnosis.

Most dogs recover in two or three weeks, though some cases advance to a more severe condition. “Secondary bacterial infections causing pneumonia are the predominate cause of death,” Dr. Dubovi says. “Awareness of the veterinary community of this infection helped to prevent the secondary bacterial infections.”

An H3N2 infected dog is most contagious during the two- to four-day incubation period when they are shedding the virus in nasal secretions but not showing signs of illness. Virtually all dogs exposed to the virus become infected; 80 percent of dogs develop a flu-like illness, and the 20 percent that do not become sick can still spread the virus to other dogs. Less than 10 percent of dogs die from H3N2 flu. 

Months after the H3N2 flu outbreak in Chicago, anecdotal reports of cases still circulate. Unlike seasonal flu viruses affecting people, dog flu occurs year-round. The crucial thing for dog owners is to be aware of the potential for an infection to occur.

“The best prevention is keeping dogs separated as much as possible,” says Dr. Dubovi. “The fewer contacts with other dogs, the less chance of a dog picking up a virus. In the big picture, all it takes is one infected dog to move to another area to start another outbreak.” 

Tips on Reducing the Risk of Dog Flu

Here are tips from preventive medicine expert Dr. Jason Stull of The Ohio State University on ways to reduce the risk of canine flu and similar diseases.

• When an outbreak occurs, avoid going to heavily populated dog areas, such as dog parks, grooming salons, boarding kennels, dog shows, and sporting events

• If you suspect a dog has been exposed to the virus, keep him or her separated from other dogs for one week and closely watch for signs of disease

• Keep sick dogs, such as those showing signs of respiratory illness, separated from all other dogs for two weeks

• Routinely clean and disinfect kennel surfaces and food and water bowls using soap and water followed by a disinfectant to help prevent illness, keeping in mind that the virus seldom survives beyond 48 hours

• Practice good hygiene and sanitation with frequent hand washing and thorough cleaning

• Do not share bowls, brushes, toys, collars, and leashes among dogs that do not live together

• Consult your veterinarian about vaccination, depending on the strain of flu  circulating, and other preventive measures


Used with permission from Today’s Breeder, Nestle Purina PetCare.

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