Influenza A virus (H3N8) in dogs with respiratory disease, Florida

Abstract

In 2004, canine influenza virus subtype H3N8 emerged in greyhounds in the United States. Subsequent serologic evidence indicated virus circulation in dog breeds other than greyhounds, but the virus had not been isolated from affected animals. In 2005, we conducted virologic investigation of 7 nongreyhound dogs that died from respiratory disease in Florida and isolated influenza subtype H3N8 virus. Antigenic and genetic analysis of A/canine/Jacksonville/2005 (H3N8) and A/canine/Miami/2005 (H3N8) found similarity to earlier isolates from greyhounds, which indicates that canine influenza viruses are not restricted to greyhounds. The hemagglutinin contained 5 conserved amino acid differences that distinguish canine from equine lineages. The antigenic homogeneity of the canine viruses suggests that measurable antigenic drift has not yet occurred. Continued surveillance and antigenic analyses should monitor possible emergence of antigenic variants of canine influenza virus.

Figure

Phylogenetic relationships among the hemagglutinin 3 (H3) genes. A) Nucleotide tree of the canine influenza virus H3 genes with contemporary and older equine H3 genes. B) Amino acid tree of the canine influenza virus H3 protein with contemporary and older equine H3 proteins. Bootstrap analysis values >80% are shown. Scale bar indicates nucleotide or amino acid substitutions per site.