The "Canine Flu" by Tom Beckett DVM

Posted with permission (phone numbers and email addresses have been removed:

First, a few comments of my own on the nature of influenza viruses. Viruses of the Influenza A group are responsible for widespread outbreaks of influenza in humans and animals. Strains of Influenza A are divided into subtypes based on two sorts of protein on their surface. The two proteins are called hemagglutinins (H) and neuraminidases (N). There are about 16 varieties of numbered H proteins and 9 varieties of numbered N proteins, so a very large number of combinations are possible. The strains of Influenza A circulating among humans in recent years have all been from subtypes H1N1, H1N2, or H3N2. The "Bird Flu" virus currently raising great concern in Asia is of the H5N1 subtype. This influenza virus identified in dogs is a quite different subtype from those mentioned above. This canine strain is a subtype H3N8 strain very closely related to a H3N8 strain that has been circulating widely in horses in North America for the past 40 years. During these 40 years there have been no documented instances of that virus strain causing disease in humans. Note that although some media headlines have called this canine influenza strain "deadly" for dogs the investigators directly involved with the virus say that the mortality rate is not high. They estimate the mortality rate for animals that develop symptoms is somewhere between 1 and 10% and probably about 5-8%. No doubt--as is true of influenza in humans and other animals--the patient's overall health status at time of infection and the timeliness and quality of medical care will affect the chances of a favorable outcome. Now for some information from authoritative sources:

Abstract of article by Dr Crawford, et al., published online 9/26/05 by "Science" magazine

CDC Media briefing of 9/26/05


A message forwarded from our TVMDL in College Station, Texas:

[Begin forwarded message:]
From: Beverlee Nix
Date: September 29, 2005 11:09:31 AM CDT
Subject: TVMDL response to media reports of canine influenza in parts of USA

The following information is forwarded to you with permission from Dr. Gayne Fearneyhough at the Texas Veterinary Medical Diagnostic Laboratory in College Station.

My apologies if this is a duplicate message for some veterinarians. "The upcoming edition of Science will contain an article on the "new canine flu" virus. The release of the abstract for that article this week has prompted a response from the news media that may be somewhat excessive. The first isolation of the virus was in Florida in 2004. The second isolation occurred at TVMDL from racing dogs in late 2004. As you can read below, eight states have reported the virus, mainly in dogs held in close confinement (kennels). TVMDL is working on developing a serologic test that may be of value to practitioners. It should be emphasized that we have not identified the virus in any other dogs in Texas during the last year, therefore, the threat to the average pet dog appears to be minimal. However, if you have clients with dogs that make the show circuit, mix with racing dogs, or are exposed to other dogs in "high risk" kennel operations, it may be wise to recommend a period of quarantine before mixing them with a general population.

To date, there has been no evidence of a public health threat associated with this virus reported to us. Below is a information note that will go out with all TVMDL cases. Gayne Fearneyhough DVM TVMDL

Newly emerging Canine Flu Virus: Reports of a new virulent strain of canine influenza (canine flu) have recently been circulating in the popular press. An H3N8 strain of influenza virus previously associated with horses was isolated in 2004 from greyhounds at a racetrack in Jacksonville, FL and subsequently found at other racetracks in Florida, Massachusetts, Arizona, West Virginia, Wisconsin, Texas, and Iowa. The more recent outbreak appears to be related to pet dogs in kennels in New York. Like most influenza viruses, the incubation period is 2-5 days, transmission can occur by aerosol, fomites, and/or contact. The symptoms are similar to "kennel cough" with the exception of high fever >105, leukopenia, and nasal discharge. Morbidity approaches 80% with mortality between 1-10%. Signs may last for 2-3 weeks depending somewhat on secondary bacterial infections. Antibiotics and fluids can reduce the fatality rate. The virus is sensitive to antiviral drugs specific for influenza A viruses however, none of these have been approved for use in dogs. Gross lesions include extensive hemorrhage in the lungs, mediastinum, and pleural cavity. Histologically a tracheitis, bronchitis, broncheolitis, and suppurative pneumonia are observed. Additionally, the epithelial lining of the airway lumen are infiltrated by neutrophils and macrophages. If influenza infection is suspected we suggest collecting serum samples (acute and convalescent, paired samples), respiratory swabs and/or transtracheal washes for isolation. Tissues (fresh and fixed) on post-mortem cases should include lungs, tracheas, and regional lymphatics. Fresh tissues for isolation should be collected as aseptically as possible, chilled to 4°C (refrigerate), and shipped on ice packs, overnight, as soon as possible.

--Dr. Lester, DVM, PhD Head, Virology Section, TVMDL" [end forwarded message]


I hope this information is helpful.

Tom Beckett, DVM Austin, Texas