There are several viruses and bacteria that cause canine infectious respiratory disease (CIRD), which is frequently called “kennel cough.”
These include bacteria such as Bordetella bronchiseptica and Streptococcus equi subsp.zooepidemicus, as well as numerous viruses including canine distemper, canine parainflueza and canine influenza.
Dr. Stephanie Janeczko, Senior Director of the ASPCA’s Shelter Medical Programs, points out that the clinical signs seen in affected dogs are very similar regardless of which pathogen they are infected with, and laboratory testing is necessary to reach a definitive diagnosis. Because these pathogens are spread efficiently between dogs, prevention and control of CIRD remains a particular challenge and health concern when dealing with dogs housed in close proximity to one another.
There are currently two canine influenza virus (CIV) strains affecting dogs in the U.S., H3N8 and H3N2. The H3N8 strain was originally detected in racing greyhounds in Florida in 2004, although there is evidence that it has been circulating in the dog population since at least 1999; infection has been reported in most states. Previously reported only in Asia, H3N2 was first noted in Chicago in 2015 and has since been reported in most other states. H3N2 was documented to affect cats in one Indiana shelter in 2016.
How CIV Is Transmitted
The virus is transmitted by direct oronasal contact as well as aerosolization of respiratory secretions from infected dogs, with an increased risk of exposure in high-density settings such as animal shelters and boarding kennels. Fomite transmission is also possible.
The incubation period is less than one week for both H3N8 and H3N2. Viral shedding for H3N8 is short, typically lasting no more than one week following infection; however dogs infected with H3N2 have been shown to shed virus for up to 3-4 weeks Peak shedding of both strains occurs very early in the course of infection and can actually precede the development of clinical signs by a few days.
Because canine influenza is still a relatively new virus and vaccination is not widespread, most dogs will be susceptible to infection. As a result, a very high incidence of upper respiratory signs can occur when the virus is introduced. There is no evidence at this time that CIV infects people.
Typical clinical signs of canine influenza infection include coughing, sneezing, nasal discharge and mild fever. Some infected dogs will remain asymptomatic; it has been estimated that up to 20% of those infected with canine influenza virus will not show clinical signs of disease.
Dr. Janeczko adds that more severe reactions, including pneumonia and even death, may occur in a small number of cases. Co-infection with other respiratory pathogens is possible and can result in more severe symptoms.