The Emerging Threat of Dog Flu in America

History of H3N8 Strain of Dog Flu

Dog Flu, also known as canine influenza virus (CIV), was first recognized in 2004 by University of Florida researchers and Cornell University virologists working with the Centers for Disease Control and Prevention following an outbreak of severe respiratory illness at a Greyhound racing facility in Florida.2,4,10

The mysterious illness first impacted Greyhounds at racing facilities in Florida in 2003 and 2004.2 In January 2004, eight of 22 affected dogs had died due to extensive hemorrhage in the lungs.4,11 Fortunately, this was a small outbreak due to the rapid institution of containment measures. Since that time, however, Dog Flu has been identified throughout the United States.1,4,12

Following the 2004 outbreak, the extent of respiratory infections in Greyhounds was established by two lines of evidence:11,14 Respiratory disease outbreaks occurred during 2004 and 2005 at racetracks in at least 13 states, representing over 20,000 dogs.

In July 2004, Dog Flu was diagnosed in a Greyhound that died at a track in Texas. The virus isolated was virtually identical with the H3N8 virus identified in Florida and confirmed the link of H3N8 to equine influenza. After the 2004 outbreak, retrospective testing of archived lab samples was conducted, which indicates that the virus infected dogs as early as 1999.11,13 The 2004 outbreak in Florida was the "canary in the mineshaft" that alerted veterinary researchers and professionals to the condition.10

From this time, documented outbreaks have confirmed the spread of the virus to the general population. In May 2009, cases of Dog Flu had been confirmed in 30 states. Since 2009, 13 more states have documented cases, and the virus continues to spread. Every continental state except one has either had a confirmed case of Dog Flu, or borders on a state that has.1

FIGURE: Canine influenza H3N8 in the United States1

H3N8 map

History of H3N2 Strain of Dog Flu

In March 2015, a severe outbreak of respiratory disease affecting over 1,000 dogs in the Chicago, IL area was documented. Merck Animal Health supported the testing of over 450 dogs at that time. The samples were sent to Cornell University's Veterinary Diagnostic Laboratory and 158 dogs were diagnosed with Dog Flu.

Shortly thereafter the virus was typed as canine influenza virus H3N2, which had never been isolated previously in the US. The virus is of avian origin and closely related to the South Korean canine influenza H3N2 strain. As of June 2017, this virus had spread to 31 states.

FIGURE: Canine influenza H3N2 in the United States1

H3N2 map