Canine Influenza
Authored by: Becky Lundgren, DVM
Canine influenza, or canine flu, is an emerging respiratory tract disease that is similar to, or mimics, bordetellosis (Bordetella bronchiseptica infection, kennel cough, infectious tracheobronchitis). However, unlike many cases of bordetellosis, the dog needs veterinary care. Canine influenza is caused by a highly contagious virus that was identified in Florida in 2005 when it caused several severe respiratory outbreaks in racing greyhounds. The disease appears to occur most frequently in high-density dog populations: dogs who are housed with numerous other dogs in places such as shelters, boarding facilities, breeding kennels, pet stores, rescue groups, dog shows, and greyhound tracks. The disease is thought to have originated as a mutation of a strain of influenza that affects horses and is not related to typical human influenza strains or the avian flu.
“This is just one more microorganism that has the potential to cause a kennel cough-like disease in dogs,” said Brad Fenwick, DVM, PhD, DACVM, University Vice President for Research and Professor of Infectious Disease Pathobiology at Virginia Tech, an infectious disease expert knowledgeable about diseases that affect racing greyhounds. “It is difficult to know how long this influenza virus has been circulating in the canine population, as efforts to determine the etiologic agent in cases of ‘kennel cough’ rarely include virus isolation, particularly for influenza virus. Periodic reports of large outbreaks of kennel cough could have been caused by this virus, but confirmation of the etiology is rare. There are historical reports of acute cases of a virus-like respiratory disease, suspected to be influenza, in dogs.”
Based on cases diagnosed over the past several years, the influenza virus appears to be as contagious as other causes of kennel cough, and it has no greater mortality (death) rate. Morbidity (illness) rates can range from 80% to 50% on the high end, and evidence indicates that perhaps 50% of infected dogs develop antibodies without showing any clinical disease at all.
“Mortality rates are certainly less than 1% and often are zero,” said Dr. Fenwick. “As with most cases of kennel cough, the clinical signs are generally mild, the disease resolves without treatment, and treatment does not noticeably alter the course and duration of the disease.” According to Dr. Fenwick, in the complex cases with a secondary bacterial pneumonia, severe clinical signs of shock and disseminated intravascular coagulopathy (DIC, a clotting problem in which bruising is caused by internal bleeding) can develop rapidly regardless of the primary infection. For dogs suspected of having canine influenza, the complication rate of cases is generally around 1%, while with other causes of kennel cough the complication rate can approach 5%.
Christopher Olsen, DVM, PhD, a professor of public health at the School of Veterinary Medicine at University of Wisconsin-Madison, led a team investigating the virus. “Signs are fever, coughing, and decreased appetite and activity levels. Although this can look quite similar to routine ‘kennel cough,’ I would suggest taking dogs to a veterinarian at the first signs of illness, as intensive supportive care can be important in reducing fatalities.”
Temperatures can quickly reach 106°F or more, but can return to near normal (or even become subnormal) as the disease progresses. The clinical onset can be rapid, with death occurring in 4 to 6 hours. “Fortunately, these cases are easily rescued with appropriate fluid and antibiotic therapy, if caught at the early stages (prior to DIC). Recovery is often just as rapid as the onset (2-4 hours) and relapses are rare,” said Dr. Fenwick. The most common bacteria involved in the secondary infection are Pasteurella multocida, Klebsiella pneumoniae, E. coli, and Streptococcus sp. Therefore, Dr. Fenwick says it is important to use a combination of antibiotics to cover both gram-positive and gram-negative bacteria.
Given the clinical characteristics of the disease, preventive use of antibiotics appears warranted only in patients that are at greater risk of secondary bacterial infections. “In short, while veterinarians may now have another cause of ‘kennel cough’ to deal with, the clinical course and treatment are the same,” said Dr. Fenwick.
In 2009, a canine influenza vaccine was released. This vaccine is not considered a "core" vaccine by veterinary experts. It can be useful for animals that are kept in high-density situations (shelters, racing kennels, boarding facilities, dog shows, etc.) where bordetellosis might also be commonly seen. The vaccine requires a booster 2 to 4 weeks after the first dose is given, and the second dose should be given at least 7 days prior to the dog entering the at-risk situation (boarding kennel, dog show, etc.) The vaccine will not prevent canine influenza, but it will help reduce clinical signs (the severity of lung lesions, the duration of coughing, and the amount of viral shedding).
Date Published: 9/29/2005 4:37:00 PM
Date Reviewed/Revised: 10/5/2009
Public Health for Hunters
Public health is always a concern in veterinary medicine. Publications for hunters are available on the American Veterinary Medical Association website (www.avma.org). One is available at the following link: Disease Prevention Quick Tips for Hunters . 11/3/09
