Canine influenza was around as early as 1999

Anderson and her colleagues were concerned that a number of respiratory outbreaks of unknown cause at greyhound tracks prior to 2004 might be an indication that the virus had been in the dog population earlier. They were able to acquire greyhound blood samples for the period 1999 to 2004 from Hemopet®, an animal blood bank in California that uses retired greyhounds as donors. They tested these samples for antibodies to both the canine influenza virus and the equine influenza virus.

“For most dogs we had 2 to 3 years’ worth of samples, so we were able to follow up with the same dog from year to year to see if it maintained antibody levels,” says Anderson.

In 1999, 33% of the samples tested positive for antibodies to both canine and equine influenza viruses. Antibodies were also detected in samples collected in 2000 (38%), 2001 (19%), 2003 (44%) and 2004 (28%). Tracking the dogs using their ear tattoos, the researchers were able to determine that seropositive greyhounds were present at tracks or farms in a number of states during respiratory disease outbreaks in 1998, 1999 and 2003.

Only 1% of the 2002 samples tested positive. Interestingly, says Anderson, there were no outbreaks that year, and most of the sampled dogs had not been on tracks during the outbreaks in 1998 or 1999.

“Based on the serological evidence, we conclude that influenza A H3N8 virus was circulating in the racing greyhound population as early as 1999. The seropositive dogs were located at tracks involved in respiratory disease outbreaks of unknown etiology, suggesting that influenza A H3N8 virus may have been the causative agent of those outbreaks,” says Anderson.

The International Conference on Emerging Infectious Diseases is organized by the Centers for Disease Control and Prevention (CDC), the American Society for Microbiology, the Council of State and Territorial Epidemiologists, the Association of Public Health Laboratories and the World Health Organization. More information on the meeting can be found online at www.iceid.org.