The CDC’s latest Emerging Infectious Diseases Journal has an article about H3N2 in dogs. Very interesting and alarming.
I’ll just reproduce the discussion:
Because all genes of the canine isolates were of avian influenza virus origin, we concluded that the entire genome of the avian influenza virus had been transmitted to the dogs. Transmission of avian influenza A virus to a new mammalian species is of great concern, because it potentially allows the virus to adapt to a new mammalian host, cross new species barriers, and acquire pandemic potential.
Transmission of an entire avian influenza virus to an unrelated mammalian species is a rare event. Several outbreaks of avian influenza infection have occurred in mammals. Influenza virus (H7N7) of avian origin was isolated from the lungs and brains of dead seals. In addition, it was replicated to high titers in ferrets, cats, and pigs and caused conjunctivitis in humans (11,12). Avian origin influenza virus (H4N5) was reported as the cause of infection and death in harbor seals along the New England coastline (13), and avian origin influenza (H5N1) infection was identified in a dog after ingestion of a duck infected with subtype H5N1 during an outbreak in Thailand in 2004 (14).
Previously, outbreaks of hemorrhagic pneumonia caused by equine influenza virus (H3N8) were noted in racing dogs, and a human influenza virus (H3N2) was isolated from dogs (15,16). However, these reports provide limited serologic and virologic evidence for influenza virus infection in dogs. We report the emergence of a new canine influenza virus strain that causes acute respiratory disease in dogs and that differs from previous outbreaks of equine influenza virus (H3N8) infections.
Concerning the possible mechanism of avian influenza virus transmission to dogs, we posit that this transmission results from feeding dogs untreated minced meats of ducks or chickens. In South Korea, untreated duck and chicken meats, including internal organs and heads, have been widely used to feed dogs for fattening in local canine farms or kennels. In a previous study, avian influenza virus (H3N2) was isolated from ducks and chickens sold at live-bird markets in South Korea. Live-bird markets are thought to constitute “a missing link in the epidemiology of avian influenza viruses” because they bring together numerous hosts, such as chickens, ducks, turkeys, geese, and doves, in a high-density setting, which represents an ideal environment for virus interspecies transmission (17,18). The S11 strain, whose HA and NA genes showed the greatest identity to those of the A/canine/Korea/01/2007 (H3N2) isolates from dogs, was isolated from a tracheal swab of a healthy chicken and is nonpathogenic in poultry (8). These observations support the hypothesis that avian influenza virus (H3N2) strains could be transmitted by feeding infected poultry by-products to dogs (2).
It is also possible that cross-species transmission of influenza virus occurs directly by aerosol transmission from infected birds to susceptible dogs as a consequence of close contact between the 2 species. Lectin-staining results showed that canine upper (trachea and bronchi) and lower (bronchiole) respiratory tract epithelium cells display SAα 2,3-gal, to which avian influenza viruses bind, making possible a direct transmission of avian influenza viruses from poultry to dogs. Additionally, according to the animal hospital veterinarian, this outbreak was traced to a Jindo dog purchased at a live-animal market in Kyunggi Province that sold chicken, duck, pheasant, rabbit, cats, pet dogs, and other dogs. The Jindo dog was hospitalized at the local animal hospital and may have infected the other pet dogs at the hospital. This epidemiologic result also suggests that the novel canine influenza virus of avian origin was transmitted within canine species.
Antigenic and phylogenetic analyses showed that the HA and NA genes of the A/canine/Korea/01/2007 (H3N2) isolate are closely related to isolates identified in 2003 from chickens and doves in South Korea. Furthermore, HA genes of canine influenza isolates were different from recent isolates from swine in South Korea (19). The other genes of the canine influenza isolate are more closely related to those of the subtype H9N2 isolate found in ducks from Hong Kong, the subtype H6N2 isolate from ducks in Japan, and several other avian influenza strains from southeastern China in 2000 through 2005. This finding suggests that multiple variants of subtype H3 influenza viruses may be circulating in these regions and causing disease in pet dogs.
Our experimental reproduction of the disease caused by this isolate induced severe pathologic changes and showed that infected dogs excreted influenza virus (H3N2) in nasal discharge but not in feces. This finding suggests that dog-to-dog transmission of subtype H3N2 could occur through the nasal route and that dog-to-dog transmission of the virus could play an important role in the epizootiology of the disease.
In our study, virologic, serologic, pathologic, and phylogenetic analyses showed cross-species infection of an entire avian influenza A virus (H3N2) to another mammalian species, dogs. Evidence of avian influenza virus infection in pet dogs raises the concern that dogs may be become a new source of transmission of novel influenza viruses, especially where avian influenza viruses are circulating or have been detected.
