Evolution of canine and equine influenza (H3N8) viruses co-circulating between 2005 and 2008

Abstract

Influenza virus, subtype H3N8, was transmitted from horses to greyhound dogs in 2004 and subsequently spread to pet dog populations. The co-circulation of H3N8 viruses in dogs and horses makes bi-directional virus transmission between these animal species possible. To understand the dynamics of viral transmission, we performed virologic surveillance in dogs and horses between 2005 and 2008 in the United States. The genomes of influenza A H3N8 viruses isolated from 36 dogs and horses were sequenced to determine their origin and evolution. Phylogenetic analyses revealed that H3N8 influenza viruses from horses and dogs were monophyletic and distinct. There was no evidence of canine influenza virus infection in horses with respiratory disease or new introductions of equine influenza viruses into dogs in the United States. Analysis of a limited number of equine influenza viruses suggested substantial separation in the transmission of viruses causing clinically apparent influenza in dogs and horses.

Epidemiology and Ecology of H3N8 Canine Influenza Viruses in US Shelter Dogs

“…Both CA and TX had no CIV‐seropositive samples and CA had only 1 dog shedding CIV upon admission into the shelter (April 2010) throughout the entire study. True prevalence estimates (Table 2) corroborate other reports suggesting CIV is endemic in CO and NY4, 5, 12, 13 with prevalence estimates of 2.7 and 2.5% for these shelters, respectively. The CIV‐positive nasal swabs collected from SC in the first 2 months of the study may explain the higher CIV‐shedding prevalence estimates for the SC shelter (1.9%) compared to the FL shelter (0.7%).…”

“…Studies conducted in nonshelter dog populations find very little CIV seropositivity in household, racing sled, and flyball tournament dogs,3, 10, 11 suggesting CIV infection to be relatively lower in dogs from the nonshelter community. In contrast, CIV is routinely detected in humane shelters throughout the United States, especially in CO and NY, where surveillance studies have been recently performed 4, 5, 12, 13…”

Current Knowledge of Interspecies Transmission of H3N8 Influenza A Virus between Horses and Dogs

“…Rivailler et al (23) found by molecular epidemiological surveillance. This finding correlates with the experimental data showing that CIV had less pathogenicity and replication ability in horses than EIV (21).…”

“…In light of the binding specificities to the SA moieties, since position 222 of the HA is located near the receptor binding site (7,8,23), W222L substitution may cause the reduced binding of CO06 to NeuGcα2-3Gal. Interestingly, W222L substitution was also found in the interspecies transmission of avian influenza A virus (H3N2) to dogs in South Korea in 2007 as well as the interspecies transmission of EIV (H3N8) to swine in China in 2005-2006 (24, 25).…”

The avian‐origin H3N2 canine influenza virus that recently emerged in the United States has limited replication in swine

“…An H3N8 equine influenza virus (EIV) initially caused outbreaks in racing greyhounds in the United States in 20042, 3; however, epidemiological and serological evidence indicated that an H3N8 equine virus introduction around 1999 was likely the ancestral strain of the H3N8 CIV in the United States 4, 5. While there was evidence of additional EIV transmission events into dogs in the United States,6 there was no evidence of sustained transmission of these other events, nor were there reports of CIV transfer back to horses or to humans 7. An H3N2 avian influenza virus (AIV) was detected in dogs in Asia in ~2005 and now appears to be endemic 8, 9, 10, 11.…”