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Canine Influenza Patterns in Shelters

Clinician's Brief (Capsule)

Infectious Disease

|July 2014

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Canine influenza virus (CIV) H3N8 was first detected in racing greyhounds in Florida in 2004 and subsequently spread to shelter populations in New York and Florida. The disease is supposedly spread by direct contact, deposition of infectious droplets on the nasal or oral mucosa, or inhalation of infectious particles. Serum and nasal swabs were collected at intake and discharge from 5,160 dogs in 6 shelters in the U.S. (CA, CO, FL, NY, SC, TX) over a 2-year period. Nasal swab positivity varied among the geographic regions (NY, 4.4%; CO, 4.7%; SC, 3.2%; FL, 1.2%; CA and TX, 0%). When data were compared at intake and discharge, trends varied among shelters. For example, in Colorado, 6 times more dogs were shedding virus at discharge (8.9%) than at intake (1.4%). In contrast, in New York, dogs were more likely to be shedding at intake (6.9%) than at discharge (1.1%). Data revealed that the disease demonstrated an ebb-and-flow pattern where outbreaks occurred in 1 shelter and 1 region and waned before the disease emerged in another shelter in another region. Dog-to-dog contact and number of days in the shelter were contributory factors for CIV seropositivity and shedding. Data indicated that community dogs were a source of CIV introduction into a shelter and that once established, dog-to-dog transmission maintained the virus within the shelter.


Upper respiratory disease is a common owner complaint in dogs recently adopted from shelters. CIV H3N8 is an emerging pathogen not easily distinguishable from other causes of upper respiratory disease. Overall prevalence in shelter dogs appeared to be low with regional and seasonal variability. Additional state-based data are necessary to classify this canine public health problem. Veterinarians advising shelters or rescue groups need to make these organizations aware of CIV and explore avenues for screening, quarantine, and control as more information becomes available. Private practitioners need to be aware of this disease as well, especially when treating dogs recently adopted from shelters and when educating clients who might be involved with local animal shelters.—Elizabeth Layne, DVM


Epidemiology and ecology of H3N8 canine influenza viruses in US shelter dogs. Pecoraro HL, Bennett S, Huyvaert KP, et al. JVIM 28:311-318, 2014.

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