5 Corners Animal Hospital   

From AVMA.org (http://www.avma.org/public_health/influenza/canine_bgnd.asp)

Backgrounder: Canine influenza
September 7, 2009
Natural distribution
The first recognized outbreak of canine influenza is believed to have occurred in racing greyhounds in January 2004 at a track in Florida. From June to August of 2004, outbreaks of respiratory disease were reported at 14 tracks in 6 states (Florida, Texas, Alabama, Arkansas, West Virginia, and Kansas). Between January and May of 2005, outbreaks occurred at 20 tracks in 11 states (Florida, Texas, Arkansas, Arizona, West Virginia, Kansas, Iowa, Colorado, Rhode Island, and Massachusetts). Since then, canine influenza has been documented in 30 states and Washington, DC. At this time, CIV is endemic (very prevalent) in areas of in Colorado, Florida, New York, and Pennsylvania.2 As of October 2, 2008, 1,079 cases of canine influenza were confirmed by the Cornell University College of Veterinary Medicine Animal Health Diagnostic Center.3

Transmission
Canine influenza is spread via aerosolized respiratory secretions and contaminated objects (kennel surfaces, food and water bowls, collars and leashes) and people moving between infected and uninfected dogs. The virus can remain viable (alive and able to infect) on surfaces for up to 48 hours, on clothing for 24 hours, and on hands for 12 hours.4

The incubation period is usually two to four days from exposure to onset of clinical signs. The highest amounts of viral shedding occur during this time; therefore, dogs are most contagious during this 2-4 day incubation period when they are not exhibiting signs of illness. 4 Virus shedding decreases dramatically during the first 4 days of illness but may continue up to 7 days in most dogs and up to 10 days in some dogs.4

Because this is a newly emerging pathogen, all dogs, regardless of breed or age, are susceptible to infection and have no naturally acquired or vaccine-induced immunity when first exposed to the virus. If the virus enters a kennel or other closed group, a high percentage of the dogs may become infected, and most of these dogs will be symptomatic.2 Approximately 20-25% of infected dogs are expected to remain asymptomatic, but can still shed the virus and spread the virus. Although most dogs have a milder form of canine influenza and recover without complications, some may develop severe pneumonia.1

Pathology and Clinical Signs
The canine influenza virus infects and replicates inside the cells of the respiratory tract, from the nasal lining to the terminal airways. The inflammatory response results in rhinitis, tracheitits, bronchitis and bronchiolitis. The pathologic process also involves the death of the epithelial cells lining the respiratory tract, resulting in exposure of the underlying basement membrane. This, in turn, predisposes the respiratory tract to secondary bacterial infections that contribute to the nasal discharge and coughing.4

Virtually all dogs that are exposed become infected with the virus, but approximately 80% develop clinical signs of disease. The approximately 20% of infected dogs that do not exhibit clinical signs of disease can still shed the virus and can spread the infection.5
However, unlike human influenza, CIV is not a "seasonal" flu – infections can occur year-round.2,4 Canine influenza virus causes clinical disease that mimics kennel cough. As a result, infection with the virus is frequently mistaken for infections caused by Bordetella bronchiseptica/parainfluenza virus complex. Clinical disease may be mild or severe.6

The majority of infected dogs exhibit the mild form of CI. In the mild form, the most common clinical sign is a cough that persists for 10 to 21 days despite treatment with antibiotics and cough suppressants. Most dogs have a soft, moist cough, whereas others have a dry cough that is similar to that induced by Bordetella bronchiseptica/parainfluenza virus infection. Many dogs have a purulent nasal discharge and a low-grade fever. The nasal discharge is usually caused by secondary bacterial infections, including Pasteurella multocida and mycoplasma species.7

Some dogs are more severely affected with clinical signs of pneumonia, such as a high-grade fever (104°F to 106°F) and increased respiratory rate and effort. Thoracic radiography (chest x-rays) may reveal consolidation of lung lobes.

Treatment
As for all viral diseases, treatment is largely supportive. Good husbandry and nutrition may assist dogs in mounting an effective immune response. In the milder form of the disease, a thick green nasal discharge most likely represents a secondary bacterial infection that usually resolves quickly after treatment with a broad-spectrum bactericidal antimicrobial. Pneumonia in more severely affected dogs responds best to a combination of broad-spectrum bactericidal antimicrobials (to combat secondary bacterial infections) and maintenance of hydration via intravenous administration of fluids. Most dogs recover from canine influenza within 2-3 weeks.4

Currently available antiviral drugs are approved for use in humans only and little is known about their use, efficacy and safety in dogs.

Deaths occur mainly in dogs with the severe form of disease; the mortality rate is thought to be 1-5% or slightly higher. Higher case fatality rates have been reported in small groups of greyhounds that developed hemorrhagic pneumonia during outbreaks.

Prevention and control
In May 2009, the USDA approved the licensure of the first influenza vaccine for dogs developed by Intervet/Schering Plough Animal Health Corporation. The canine influenza vaccine contains inactivated whole virus.8,9

The vaccine is intended as an aid in the control of disease associated with CI virus infection. Although the vaccine may not prevent infection altogether, efficacy trials have shown that the vaccination may significantly reduce the severity and duration of clinical illness, including the incidence and severity of damage to the lungs.4 In addition, the vaccine reduces the amount of virus shed and shortens the shedding interval; therefore, vaccinated dogs that become infected develop less severe illness and are less likely to spread the virus to other dogs.9 These benefits are similar to those provided by influenza vaccines used in other species, including humans.

The canine influenza vaccine is a "lifestyle" vaccine, and is not recommended for every dog.4 In general, the vaccine is intended for the protection of dogs at risk for exposure to the CI virus, which include those that either participate in activities with many other dogs or are housed in communal facilities, particularly where the virus is prevalent. Dogs that may benefit from canine influenza vaccination include those that receive the kennel cough (Bordetella/parainfluenza) vaccine, because the risk groups are similar.5 Dog owners should consult with their veterinarian to determine whether their dog's lifestyle includes risks for exposure to the CI virus, and if the vaccine is appropriate for their dog.6, 9

More information can be found at:
http://www.avma.org/public_health/influenza/canine_guidelines.asp
http://www.avmamedia.org/display.asp?sid=184&NAME=Canine_Influenza
http://www.cdc.gov/flu/canine/
http://www.vetmed.ufl.edu/college/pr/documents/CanineinfluenzaFAQDogowners_001.pdf
http://www.diaglab.vet.cornell.edu/issues/civ.asp
References

  1. Meyer M. UF veterinary researchers discover a new disease in dogs. Explore: Research at the University of Florida; 2006:11. Available at: http://www.research.ufl.edu/publications/explore/v11n2/story3.html. Accessed on August 19, 2009.
  2. Crawford C. Canine influenza: Frequently asked questions from dog owners. University of Florida; 2009. Available at: http://www.vetmed.ufl.edu/college/pr/documents/CanineinfluenzaFAQDogowners_001.pdf . Accessed on August 19, 2009.
  3. Cornell University: College of Veterinary Medicine. Emerging issues - Canine influenza: Test summary for canine influenza virus in dogs not affiliated with greyhound racetracks Animal Health Diagnostic Center. Available at: http://www.diaglab.vet.cornell.edu/issues/civ-stat.asp. Accessed on August 19, 2009.
  4. Crawford C. Canine influenza: Frequently asked questions from veterinarians. University of Florida; 2009. Available at: http://www.vetmed.ufl.edu/college/pr/documents/CanineinfluenzaFAQ.Veterinarians_000.pdf . Accessed on September 3, 2009.
  5. Iowa State University. Canine Influenza 2009. Available at: www.cfsph.iastate.edu/Factsheets/pdfs/canine_influenza.pdf. Accessed on August 19, 2009.
  6. Control of canine influenza: Questions, answers, and interim guidelines. American Veterinary Medical Association; 2005. Available at: http://www.avma.org/public_health/influenza/canine_guidelines.asp. Accessed on August 19, 2009.
  7. Cornell University: College of Veterinary Medicine. Emerging issues - Canine influenza virus. Animal Health Diagnostic Center; 2006.Available at: http://www.diaglab.vet.cornell.edu/issues/civ.asp . Accessed on August 19, 2009.
  8. United States Department of Agriculture. Animal and Plant Inspection Service. Veterinary Services: Center for Veterinary Biologics. Center for Veterinary Biologics Notice No. 09-13. Issuance of Licenses. 2009. Available at: http://www.aphis.usda.gov/animal_health/vet_biologics/publications/notice_09_13.pdf. Accessed on August 19, 2009.
  9. Cole, L. McNally, A. APHIS issues conditional license for canine influenza virus vaccine. United States Department of Agriculture. Animal and Plant Inspection Service; 2009. Available at: http://www.aphis.usda.gov/newsroom/content/2009/06/caninevacc.shtml. Accessed on August 19, 2009.

This information has been prepared as a service by the American Veterinary Medical Association. Redistribution is acceptable, but the document's original content and format must be maintained, and its source must be prominently identified. Please contact Sheila Saldeen (800.248.2862, ext 6740; ssaldeen@avma.org) or Dr. Kimberly May (800.248.2862, ext 6667; kmay@avma.org) with questions or comments.