WHAT IS CANINE INFLUENZA?
Influenza viruses have a unique ability to mutate and form new strains. This process of change is called "antigenic drift" and produces new strains of influenza that infect the same host species. (It is because of antigenic drift that we need a new vaccine for flu each flu season. Sometimes these mutations, lead to a strain being able to cross over into a new species.) Type A influenza viruses can do more; however. They can actually reorganize their surface proteins to facilitate crossing from one species to another and creation of a vastly different different new flu virus. This process of change is called "antigenic shift" and usually occurs within the body of a bird or pig. The new viruses that are created by this process are more likely to be able to jump to a new species than those created by the simple mutations of antigenic drift (which is why "swine flu" and "avian flu" are portrayed as particularly ominous in relation to human infection).
Despite all this mutation and recombining, influenza viruses generally keep to the same host species. Neither of the two canine influenza viruses is transmissible to humans. The H3N2 (Asian) canine influenza virus is able to infect cats as can the H7N3 (bird) influenza virus. The H3N8 canine influenza virus has not been known to infect cats. The H1N1 influenza virus that was involved in the human pandemic of 2009 can also infect cats but cats do not shed virus back in amounts likely to infect humans. As a general rule, humans infect other humans and household pets are not involved in transmission of flu to humans.
WHAT HAPPENS TO THE SICK DOGS?
Infection rate is high but (depending on which report one reads) 20-50% will simply make antibodies and clear the infection without any signs of illness at all.
The other 50-80% will get symptoms of the “flu:” they will have fevers, listlessness, coughing, and a snotty nose. Most dogs will recover with supportive treatment (antibiotics, perhaps nebulization/humidification, etc.). A small percentage of dogs will actually get pneumonia. These dogs are those at risk for death and support becomes more aggressive: hospitalization, intravenous fluid therapy etc. Most of these dogs will recover as well, as long as they receive proper care. Mortality rate is 5-8%
The incubation period is 2-5 days and the course of infection lasts 2-4 weeks. Because this is an emerging disease, few dogs will have immunity to it unless they have received one of the new vaccines. This means that any dog unvaccinated for influenza is a candidate for infection.
HOW IS THE DISEASE TRANSMITTED?
HOW ARE SICK DOGS TREATED?
High fevers are treated with anti-pyretic medications or cool water baths, but generally antibiotics to control secondary infections are all that is needed. Pneumonia results from secondary bacterial infections (i.e. bacteria invading the lung after the virus has damaged the tissue and compromised its ability to defend itself). Pneumonia in the dog is virtually always secondary in this way (meaning that an initial condition damages the lung allowing bacterial invaders to settle in) and treatment is similar regardless of the cause. For details click here.
CAN DOGS GET REINFECTED?
After a dog has recovered from canine influenza, immunity appears to last at least 2 years.
HOW ARE DOGS TESTED FOR CANINE INFLUENZA?
In a perfect world there would be a simple test that could be performed on a single sample and yield unequivocal results. There are two main ways to confirm canine influenza infection:
DOES VACCINATION AGAINST “KENNEL COUGH” (BORDETELLA) OR PARAINFLUENZA OFFER ANY PROTECTION AGAINST CANINE INFLUENZA?
No. In fact, H3N8 requires a separate vaccine from H3N2. There is no vaccine that covers both strains though both Merck and Zoetis manufacture vaccine against H3N8 and Zoetis presently has conditional approval on a vaccine for H3N2. Currently, vaccination against H3N2 is of some controversy for, even though there was an outbreak of extreme scale in this country, many feel that now that containment has been achieved it is unlikely that it will occur again. (H3N2 had previously been limited to South Korea but was introduced through rescue programs that bring Asian dogs to the U.S. for better life and adoption). Vaccination for H3N8 should be considered for dogs at increased exposure risk: dogs that attend doggie daycare, who regularly go to the grooming parlor, who travel for show purposes, or who regularly play with other dogs at the park. The flu is no fun for anyone and has potential to be life-threatening. In most influenza situations, it is the very young and very old who experience the most severe disease but during the H3N2 outbreak, most infected dogs were healthy and middle-aged.
WHY DON'T DOGS NEED A DIFFERENT FLU SHOT EACH YEAR LIKE PEOPLE DO?
Earlier in this article, we discussed "antigenic drift." One of the defining features of the influenza viruses is their ability to mutate. Every time the virus infects a new person, the virus rapidly replicates as part of the infection process. Every time the virus replicates, there is potential for mutation. Some mutated forms of virus are ineffective and die off while others are very effective and continue spread through the community. It is because of all this contagion and replication that the human influenza virus is able to mutate into a new version of itself each flu season. Each new version is different enough that the old vaccine is probably not going to work and a new vaccine must be developed.
The dog situation is a bit different. A human being can easily have contact with hundreds of people daily depending on the nature of their job and whether they use public transportation. This is a huge potential to spread disease. The average dog, however, lives in his home mostly and usually does not see other dogs unless he goes out into a public area where there are many other dogs. This amounts to far less potential for the virus to spread and mutate and so far the original H3N8 vaccines are still effective. As noted, the H3N2 vaccine is new and is still conditionally licensed.
CAN PEOPLE GET INFECTED?
People cannot get infected by this virus. Influenza viruses are specific for their host species and require a dramatic mutation in order to jump species.? One should not be concerned about getting an influenza infection from a dog, horse, or any other species other than a fellow human being.
For additional information, see the links below:
Merck Animal Health has information on the Canine Influenza Vaccine, H3N8 at:
Zoetis page for pet owners on Canine Influenza:
Page last updated: 2/22/2017