An outbreak of respiratory disease in dogs occurred in the metropolitan Chicago area, beginning in March 2015.1 In early April 2015, the respiratory disease outbreak was found to be associated with an influenza virus infection in sheltered dogs. The virus was first recognized as canine influenza A H3N2 virus approximately 1 week later on April 13, 2015.1 Infections were initially reported for pet dogs with exposures reportedly occurring in veterinary clinics, day care and boarding facilities, and training centers. Dogs in ≥ 8 animal shelters in the area became severely affected, with almost 200 dogs in shelters testing positive for H3N2 virus in April, May, and June. Most dogs in those shelter populations had clinical signs of respiratory disease and a honking cough.
Two continuously circulating canine influenza A viruses have been identified, the H3N8 and H3N2 strains.1 The CDC, to date, has not reported human infections with either of the canine influenza viruses, but in 2004, H3N8 virus was reported to cross species from horses to dogs in North America2 and in 2013, H3N2 virus reportedly infected cats in an animal shelter in South Korea.3 Canine influenza A H3N8 virus was first identified in the United States in racing Greyhounds in 2004.2 Following the initial reports, H3N8 infections have occurred sporadically and caused some regionally endemic respiratory disease in animal shelters. Prior to the 2015 epidemic in the Chicago area, canine influenza A H3N2 virus had been only reported in China, Thailand, and South Korea since 2007.4
Reports of prolonged shedding of H3N2 virus in experimentally infected dogs prompted an evaluation of the 7-day isolation period previously recommended for H3N8 virus.5,6 Two studies5,7 from South Korea have reported on shedding of H3N2 virus. In otherwise healthy dogs, virus shedding has been shown to extend to 8 days for H3N2,5 whereas prolonged H3N2 shedding has been described in experimentally immune compromised and infected dogs7; immune suppressed dogs shed H3N2 virus for 13 days, compared with 8 days for control dogs. Duration of virus shedding may have important implications for the ecology and spread of the virus as well as have substantial implications for population management in a shelter setting. The purpose of the study reported here was to provide information on canine influenza A H3N2 virus outbreaks in dogs in shelters and companion animal practices in North America and to determine an appropriate isolation period for dogs infected with H3N2 virus on the basis of the duration of virus shedding.
Supported by Maddie's Fund and the WVDL.
American Association of Veterinary Laboratory Diagnosticians
Madin-Darby canine kidney
Real-time reverse transcriptase PCR
Wisconsin Veterinary Diagnostic Laboratory
Remel M-6, Thermo Fisher Scientific, Lenexa, Kan.
Kingfisher, Thermo Fisher Scientific, Vanta, Finland.
MagMAX-96 Viral RNA Isolation Kit (AM1836), Thermo Fisher Scientific, Vilnius, Lithuania.
Applied Biosystems 7500 Fast, Thermo Fisher Scientific, Singapore.
Functional Biosciences, Madison, Wis.
CCL-34 ATCC Manassas, Va.
H3N8 killed virus, Zoetis Vanguard, Florham Park, NJ.
1. CDC. Update on Canine Influenza (Dog Flu) Outbreak Reported in Chicago Area. Available at: www.cdc.gov/flu/news/canine-influenza-update.htm. Accessed Apr 13, 2015.
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