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Canine Influenza
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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 recently
identified in Florida. Several severe respiratory outbreaks in racing greyhounds
were caused by this virus. 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, clinics, 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.
“Clearly there is a great deal of concern related to this emerging story,”
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.
“There is also much misinformation. This is just one more microorganism that
has the potential to cause a kennel cough-like disease in dogs. 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 hundreds of suspected cases in greyhounds over the past year, the
influenza virus appears to be as contagious as other causes of kennel cough,
and it has no greater mortality 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 with out 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, leads 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, if caught at the early stages (prior to DIC), with
appropriate fluid and antibiotic therapy. 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 for both
gram-positive and gram-negative bacteria.
Given the clinical characteristics of the disease, prophylactic 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.
Dr. Olsen’s lab offered expertise in equine influenza viruses and provided
unpublished equine influenza virus genetic sequence information to the Centers
for Disease Control and Prevention (CDC) to help in the characterization of
the virus from dogs. “My laboratory is currently collaborating with the laboratory
of Dr. Gabriele Landot at Colorado State University to develop a cell culture
system that will allow us to study the pathogenesis of influenza virus infections
in respiratory epithelial cells (the cell type that lines the trachea and
bronchi) in the laboratory,” said Dr. Olsen.
For additional information:
http://www.cdc.gov/od/oc/media/transcripts/t050926.htm
http://avma.org/onlnews/javma/oct05/x051015b.asp
http://doacs.state.fl.us/press/2005/09202005.html
Copyright
2005 - 2007 by the Veterinary Information Network, Inc. All rights reserved.
This work was originally published by Veterinary Information
Network, Inc. (VIN) and is republished with VIN's permission.
The above information is simply informational.
It's intent is not to replace the advice of a veterinarian nor to assist
you in making a diagnosis of your pet. Please consult with your own veterinarian
for confirmation of any diagnosis. Your pets life may depend on it.