August 02, 2016

Clinical Signs & Diagnosis of Canine Influenza

Although dogs were typically considered to be refractory to infection with influenza A viruses, two canine influenza virus (CIV) subtypes—H3N8 and H3N2—have emerged in the past 12 years.
By Nicola Parry, BSc, MSc, BVSc, Dip. ACVP
Although dogs were typically considered to be refractory to infection with influenza A viruses, two canine influenza virus (CIV) subtypes—H3N8 and H3N2—have emerged in the past 12 years. Studies have shown that H3N8 CIV originated from cross-species transmission of an equine influenza A virus subtype H3N8, while H3N2 originated in avian species.1
 
CIV has, therefore, now been added to the list of several pathogens with a causative role in the canine infectious respiratory disease (CIRD) complex (CIRDC). However, although CIRD is typically associated with mild to moderate, self-limiting upper respiratory tract (URT) infection, outbreaks of canine influenza have resulted in significant morbidity and mortality in affected dogs.2 


CANINE INFLUENZA VIRUS SUBTYPE H3N8

H3N8 CIV was first identified as a novel canine pathogen after the first recognized outbreak of canine influenza in the world, which occurred in 2004 in racing greyhounds in Florida.3 It was also later associated with outbreaks of acute respiratory disease in racing greyhounds and other dogs in other states.4,5 


CANINE INFLUENZA VIRUS SUBTYPE H3N2

H3N2 CIV was first identified in the United States in 2015, after an outbreak of canine influenza—which began in March in dogs in Chicago—affected more than 1,000 dogs in the Midwest.6 From March 8, 2015, to February 2, 2016, H3N2 CIV has been identified in 30 states.7
 
Studies have shown that H3N2 CIV can infect both dogs and cats, and although rare, feline infection with CIV has been documented in the United States.8 In particular, at one Indiana shelter in early 2016, multiple cats with signs of URT tested positive for H3N2 CIV. The virus was also shown to be able to spread from cat to cat.9 However, there is no evidence, to date, of transmission of CIV from dogs to people, and no cases of CIV infection in humans have been reported.6 


TRANSMISSION OF CIV

CIV is highly contagious, and dogs of all ages and breeds are considered susceptible to infection.7 The virus spreads from dog to dog by both direct contact (via aerosolized droplets from coughing or sneezing) and indirect contact (via fomites, such as contaminated bowls). The incubation period is 2 to 5 days. Peak viral shedding occurs about 2 to 5 days after infection, but before the onset of clinical signs, making it difficult to prevent transmission to other dogs.10 In particular, such environments as boarding kennels, daycare facilities, and animal shelters—in which many dogs are in close contact, often in a restricted space—allow for rapid viral spread.7
 


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