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Canine Influenza Virus (H3N8, H3N2)

Canine Influenza Virus, H3N8, a respiratory pathogen of dogs and a component of Canine Infectious Respiratory Disease Complex (CIRDC), was first isolated in Florida in 2004 and is thought to be of equine origin. The H3N8 canine influenza strain has been identified in at least 40 states in the United States (US). In the spring of 2015, another strain of canine influenza, H3N2, was identified in an explosive outbreak of respiratory disease in the Chicago area. In less than 6 months, the H3N2 strain spread to nearly half of the continental states. The H3N2 influenza strain was previously identified in dogs in South Korea, China and Thailand. Genetic sequence analysis has categorized the H3N2 strain found in the US as a South Korean avian strain. As of June 2016, CIV H3N2 was found in 30 states.

Etiology and Pathogenesis
Canine influenza virus (CIV) is highly contagious and rapidly spread by a combination of aerosols, droplets, and direct contact with respiratory secretions or contaminated fomites. The clinical signs of canine influenza virus infection usually begin less than 5 days after infection and are very similar to those of CIRDC due to other causes such as Bordetella bronchiseptica or other respiratory viruses (eg, parainfluenza, adenovirus type 2, canine respiratory coronavirus, canine herpesvirus). CIV cannot be distinguished from these other causes of acute respiratory disease based on clinical signs alone. The course of canine influenza is mild in most dogs, but some dogs develop a more severe form with pneumonia and/or systemic illness.

Clinical and Pathological Findings
Approximately 80% of dogs, exposed to canine influenza virus H3N8, develop clinical disease, with most of these having a mild disease course. Up to 5-8% of dogs may progress to a more severe form of the condition – including fatalities. A subset of about 10 to 20% of dogs develop subclinical infection, but can still shed the virus and transmit disease to other dogs. The clinical course and pathology of canine influenza, H3N2 is under investigation.

Canine Influenza

Strain

H3N2

H3N8

Origin

Avian

Equine

Asia 2005

US 2004

Prevalence

30 States as of June 2016

40 States in 11 years

Infectious up to

24 days

14 days

Shedding

24 days, intermittent

5 days

Clinical Signs

Infectious respiratory secretions, coughing, fever

Coughing, sneezing, nasal discharge, fever

Infects

Dogs and cats

Dogs

Similarities

à Highly infectious

à Spread by direct contact with infectious respiratory secretions or by indirect contact with fomites (kennel surfaces, bowls, etc.) or people carrying the virus on hands and clothes.

à Can result in hemorrhagic pneumonia

à High morbidity, relative low mortality

Diagnosis
A definitive diagnosis of canine influenza can be made using laboratory testing, but timing of sample collection is critical and is related to the time of initial exposure and peak viral shedding. In early cases, diagnostic methods aimed at detection of the virus are preferred, including antigen detection methods, polymerase chain reaction (PCR)-based assays, and virus isolation. Nasal and/or caudal pharyngeal swabs are used for these tests. Optimally, swabs should be collected from dogs with early clinical signs (1 to 3 days post-exposure) to coincide with peak virus shedding. Alternatively, serology to detect CIV-specific antibodies can be used for confirmation of CIV infection. CIV-specific antibodies can be detected in a hemagglutination inhibition assay as early as 7 days postinfection; however, reliable detection occurs after 10 days of clinical signs. The presence of antibodies indicates exposure, but is not necessarily indicative of active infection. To confirm recent infection, it is necessary to document seroconversion (a four-fold or greater rise in antibody titer). The presence of antibodies indicates exposure, but is not necessarily indicative of active infection. To confirm recent infection, it is necessary to document seroconversion (a four-fold or greater rise in antibody titer) by comparing an acute titer with a convalescent titer (taken at least 2 weeks later).

Source: http://www.doginfluenza.com

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