Hot Literature: Keep current on canine influenza

The Animal Health Diagnostic Center of the Department of Population and Diagnostic Sciences at Cornell University has produced an update on canine influenza in the United States. The history of canine influenza virus began with the identification of infections in racing greyhounds, directing research that defined canine influenza virus (CIV), a variant of equine influenza virus with a unique genetic signature capable of being transmitted from dog to dog. However, influenza is just one of many viruses, bacteria, and mycoplasma known to cause acute respiratory disease in dogs (ARDD). The review details the history and current data available for influenza viruses that have been isolated from dogs.

H3N8-

• Isolated from racing greyhounds (2004)

• Related to equine influenza virus (EIV H3N8)

• Dog-to-dog transmission involved

• Isolated from companion dogs in Florida, New York City, and Denver

• Transmission among dogs in group housing situations

• Not highly contagious (low amounts of virus shed and no carrier state)

H5N1-

• Capable of infecting felines

• Infection result of consuming infected poultry

• Canine case reported in Thailand (2004)

• No evidence of contact transmission

• Considered "dead-end" infections with "no significance for the health of the canine population"

H3N2 -

• Isolated in South Korean dogs (2007)

• Capable of increased virus shedding (as compared with CIV) in experimentally infected dogs

• Possible dog-to-dog transmission

• Has not infected any dogs outside of South Korea

H1N1-

• Two undocumented reports of canine infection

• Not circulating in the canine population

• Infections possibly due to contact with infected owners

Clinical signs of CIV include lethargy, anorexia, nasal discharge, sneezing, depression, ocular discharge, and cough or sometimes simply a low-grade fever lasting several days. These signs are not diagnostic of influenza virus and are indistinguishable from those of ARDD caused by other pathogens. In naturally acquired CIV infections, secondary bacterial infections can lead to more serious conditions such as bronchopneumonia.

In experimental CIV infections, the pathophysiology occurs in the absence of secondary infectious agents. The upper respiratory tract lesions that develop early in the infection are consistent with tracheitis and bronchitis, thus the ciliated epithelial cells are damaged and respiratory tract defense is severely compromised. Lower respiratory tract lesions worsen later in the infection. Petechial hemorrhages and consolidated areas of the lung have been seen in association with an increase in clinical signs. Results of histologic examination reveal tracheobronchitis, bronchiolitis, and alveolitis. The animals with these lesions had negative test results for other pathogens, indicating that influenza virus alone can cause marked pathology.

Regardless of the causative agent of ARDD, the clinical presentation and treatment strategies are the same. Diagnosing the specific agent involved is not likely to be cost-effective or benefit the patient in most single-pet cases. Where the isolation of a specific pathogen becomes useful is in cases of kennel, shelter, or day-care facilities experiencing an outbreak of ARDD in which specific management approaches and movement restrictions may need to be implemented. The use of antiviral drugs is not encouraged in most situations. Since their use needs to be initiated early in the infection cycle, when most owners would not yet be considering a visit to the veterinarian, their use is not warranted. Furthermore, there are currently no data reporting the efficacy of these drugs for treating CIV, and, as the report states, their use is "an invitation for the selection of drug-resistant variants."

While there is a vaccine for CIV available for dogs in the United States, it is important to note that it does not prevent infection, but rather it can decrease virus shedding and the severity of lung pathology associated with infection. There are presently no data on the duration of immunity provided by the vaccine, but annual vaccination is recommended. For higher risk situations such as shelters or boarding facilities, the vaccine may be recommended similar to traditional kennel cough vaccines. Currently, outbreaks of dog-to-dog transmission of CIV are geographically limited within the United States. For all influenza viruses, genetic drift is ongoing and more cases and new subtypes are likely to be isolated from dogs, necessitating ongoing surveillance and study.

Dubovi EJ. Canine influenza. Vet Clin North Am Small Anim Pract 2010;40(6):1063-1071.

Link to abstract: http://www.vetsmall.theclinics.com/article/S0195-5616(10)00092-6/abstract