| Canine influenza virus (CIV) first emerged in dogs at a Florida racing track in 2004, although serological evidence suggests the virus has been circulating in the Unites States since as early as 1999. Phylogenetic analysis shows that CIV isolates are related to equine influenza virus of the Florida Clade 1 sublineage. However, sustained transmission of CIV among dogs and further genetic evolution of the virus has established CIV as a canine-specific influenza A virus (IAV). During the early years after emergence, studies determining the impact of CIV on dog populations were scarce. The few published findings were also alarming, with case fatality rates as high as 36% and seropositivity as high as 97% in certain dog populations. Despite these reports, the prevalence of CIV infection in dogs, the transmission dynamics among dog populations, risk factors for CIV infection, and how the virus was evolving within the canine host had yet to be examined. The research described here sought to fill these knowledge gaps by accomplishing four main objectives: (1) to evaluate diagnostic tests for detecting CIV infection in nasal swab samples and to determine which test(s) would be most sensitive for rapid and accurate CIV diagnosis, (2) to estimate the seroprevalence of CIV antibodies in several dog populations, including household pet, racing sled, and shelter dogs, and to evaluate any risk factors associated with CIV seropositivity, (3) to identify epidemiological and ecological determinants of CIV infection within U.S. shelter dogs, and (4) to determine the degree of genomic evolution and antigenic variability of CIV in U.S. dogs.;For the first objective, nasal and pharyngeal swab samples were collected from 124 shelter and household dogs seen at Colorado State University Veterinary Teaching Hospital (CSU VTH) for canine infectious respiratory disease between April 2006 and March 2007 and from 1372 dogs housed in six shelters from December 2009 to November 2010.;Objective two was addressed using data from three different studies. In the first study, to determine seroprevalence and risk factors for CIV in Colorado household dogs, serum samples from 140 dogs presenting to the CSU VTH Community Practice service, 110 dogs seen at other clinical services in 2009, and samples from 75 dogs seen prior to 2004 were tested with hemagglutination inhibition (HI) assay, using three CIV isolates. A similar study was conducted in sled dogs from the United States and Canada racing in the 2010 Iditarod to determine the seroprevalence of CIV in the sled dog population. For the third study, which also sought to address the third objective, risk factors for both CIV-shedding and CIV-seroprevalence in shelter dogs were examined, as well as transmission dynamics between shelter and community dogs.;Finally, the last objective was addressed by a study focused on the evolution of CIV to determine if antigenic drift is occurring, especially since the widespread use of a recently developed killed CIV vaccine. To this end, the full-length hemagglutinin gene of 19 CIV isolates from dogs sampled from Colorado, New York, and South Carolina humane shelters were sequenced. Both the nucleotide and amino acid sequences were compared to all those published for CIV strains isolated since 2003. Phylogenetic analysis suggests that CIV is diverging into two genetically distinct clades. Using a mixed-effects model for evolution (MEME), five amino acid sites were found to be undergoing episodic selection pressure: 107, 169, 216, 453, and 464. Additionally, a total of five amino acid changes were observed in two antigenic sites for CIVs isolated from the New York and South Carolina humane shelters between 2009 and 2011 (H75Q, K172E, N216H, V223I, and P262T). Although preliminary data suggest that the New York clade is evolving into a distinct antigenic cluster, controlled experiments are required to determine true extent of antigenic drift occurring within circulating CIV. (Abstract shortened by UMI.)... |
