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

Abstract

BackgroundH3N8 canine influenza virus (CIV) infection might contribute to increased duration of shelter stay for dogs. Greater understanding of factors contributing to CIV within shelters could help veterinarians identify control measures for CIV.ObjectivesTo assess community to shelter dog CIV transmission, estimate true prevalence of CIV, and determine risk factors associated with CIV in humane shelters.Animals5,160 dogs upon intake or discharge from 6 US humane shelters, December 2009 through January 2012.MethodsA cross‐sectional study was performed with prospective convenience sampling of 40 dogs from each shelter monthly. Nasal swabs and serum samples were collected. Hemagglutination inhibition and real‐time reverse transcriptase‐polymerase chain reaction assays were performed for each nasal and serum sample. True prevalence was estimated by stochastic latent class analysis. Logistic regression was used to identify risk factors associated with CIV shedding and seropositivity.ResultsNasal swabs were positive from 4.4% of New York (NY), 4.7% of Colorado (CO), 3.2% of South Carolina, 1.2% of Florida, and 0% of California and Texas shelter dogs sampled. Seropositivity was the highest in the CO shelter dogs at 10%, and NY at 8.5%. Other shelters had 0% seropositivity. Information‐theoretic analyses suggested that CIV shedding was associated with region, month, and year (model weight = 0.95) and comingling/cohousing (model weight = 0.92).Conclusions and Clinical ImportanceCommunity dogs are a likely source of CIV introduction into humane shelters and once CIV has become established, dog‐to‐dog transmission maintains the virus within a shelter.

Risk reduction and management strategies to prevent transmission of infectious disease among dogs at dog shows, sporting events, and other canine group settings

“…This has been illustrated in several documented outbreaks of canine infectious disease, 7,35,39,57,99,100 in which high population density or an increase in direct contact among dogs were evident and considered to have contributed.…”

“…36,37 When evidence exists to indicate ongoing transmission of a vaccine-preventable strain of CIV in a region, vaccination should be encouraged for all dogs traveling to or from that region to participate in a group setting. [56][57][58] Similar to the situation with core vaccines, delivery of noncore vaccines should be timed to allow for maximum protection at time of anticipated dog exposure. 17,24 Recommendation: Noncore vaccines (eg, against Leptospira spp, B burgdorferi, or CIV) should be considered on the basis of the epidemiologic characteristics of those pathogens specific to the setting location when expected activities pose an elevated risk of transmission (category II).…”

Influenza Virus Reservoirs and Intermediate Hosts: Dogs, Horses, and New Possibilities for Influenza Virus Exposure of Humans

“…However, despite these spillover events, only one EIV transfer that occurred around 1999 in the United States resulted in the establishment of H3N8 canine influenza virus in dogs in Florida, which involved the transmission of a single EIV strain from horses. This outbreak was first described in 2004 as the cause of disease among racing greyhounds, and the virus was transferred within a year to racing tracks in many parts of the United States (26) and, subsequently, to other dog populations and breeds where it has been maintained ever since (27,28). Notably, H3N8 CIV appears to have been primarily maintained since about 2008 in animal shelters in a few large cities where dogs live in dense populations and where susceptible animals are introduced at high rates (27,29,30).…”

“…This outbreak was first described in 2004 as the cause of disease among racing greyhounds, and the virus was transferred within a year to racing tracks in many parts of the United States (26) and, subsequently, to other dog populations and breeds where it has been maintained ever since (27,28). Notably, H3N8 CIV appears to have been primarily maintained since about 2008 in animal shelters in a few large cities where dogs live in dense populations and where susceptible animals are introduced at high rates (27,29,30). Because infected dogs are frequently transferred from these shelters, the virus is often passed to other dog populations where it causes outbreaks but where it is seemingly unable to sustain long-term transmission, likely because of overly heterogeneous contact networks (27,29).…”

“…Notably, H3N8 CIV appears to have been primarily maintained since about 2008 in animal shelters in a few large cities where dogs live in dense populations and where susceptible animals are introduced at high rates (27,29,30). Because infected dogs are frequently transferred from these shelters, the virus is often passed to other dog populations where it causes outbreaks but where it is seemingly unable to sustain long-term transmission, likely because of overly heterogeneous contact networks (27,29). In particular, although there are an estimated 80 million susceptible household dogs in the United States, they appear to lack the degree of contact necessary for continuous transmission of influenza virus such that chains of transmissions quickly die out (29).…”