Susceptible dogs were brought into contact with dogs experimentally infected with an avian-origin influenza A virus (H3N2) that had been isolated from a pet dog with severe respiratory syndrome. All the experimentally infected and contact-exposed dogs showed elevated rectal temperatures, virus shedding, seroconversion, and severe necrotizing tracheobronchitis and bronchioalveolitis.
Transmission of highly pathogenic avian-origin canine influenza A viruses (H3N2) that spread across South Korea during May through December 2007 was observed repeatedly in the country's animal clinics (1). These viruses share [greater than or equal to] 97% nucleotide sequence homology, suggesting that whole viruses were transmitted directly from birds to dogs. To determine whether these viruses can be transmitted directly from dog to dog, we experimentally infected beagles by direct contact. Dog-to-dog transmission of the virus raises questions about the interspecies transmission of avian influenza viruses and adaptation of these viruses to canine physiology.
Dogs in the study comprised 3 groups of beagles housed in different rooms of the isolation facility at Green Cross Veterinary Products (Yong-in, South Korea). The virus used was avian-origin canine influenza virus A/ canine/01/2007, subtype H3N2, which had been isolated from a pet dog with severe respiratory syndrome. In the first group (challenge group), 4 beagles were inoculated intranasally with a [10.sup.6.5] 50% egg infectious dose ([EID.sub.50]. Two hours later, the second group of 4 uninfected dogs (exposure group) was housed in the same contaminant room. These uninoculated dogs had frequent direct nose-to-nose contact with the inoculated dogs. The third group of 4 dogs (control group) was housed separately as uninoculated controls. Rectal temperatures were checked and nasal swab samples were collected daily. We monitored clinical signs of infection 7 days postinoculation (dpi) and examined nasal swabs obtained 10 dpi for virus shedding; serum samples were collected at 0, 3, 7, 9, and 13 dpi. Serum antibodies against nucleoprotein were detected by using a commercial competitive ELISA (Animal Genetics, Inc., Suwon, South Korea). On 7...