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Canine
Influenza
In mid 2005, University of Florida researchers reported that outbreaks
of canine influenza virus, causing an acute respiratory infection,
have been identified in dogs in shelters, humane societies, boarding
facilities and veterinary clinics in Florida , predominantly in
Broward, Dade, Palm Beach and Duval counties.
This highly contagious virus is a newly emerging respiratory pathogen
in dogs and causes a clinical syndrome that mimics kennel cough.
Canine influenza virus infections are frequently mistaken for infections
due to the Bordetella bronchiseptica/ parainfluenza virus complex
.
Because this is a new virus, all dogs, regardless of breed or
age, are susceptible to infection and have no naturally acquired
or vaccine-induced immunity. Virtually 100 percent of exposed dogs
become infected. Nearly 80 percent have clinical signs. There are
two general clinical syndromes – the milder syndrome and a
more severe pneumonia syndrome. The milder disease syndrome occurs
in most dogs.
Symptoms
In the milder disease, the most common clinical sign is a cough
that persists for 10 to 21 days despite therapy with antibiotics
and cough suppressants. Most dogs have a soft, moist cough, while
others have a dry cough similar to that induced by Bordetella bronchiseptica/
parainfluenza virus infection. Many dogs have purulent nasal discharge
and a low-grade fever. The nasal discharge likely represents a secondary
bacterial infection that quickly resolves with treatment with a
broad-spectrum, bactericidal antibiotic.
Some dogs develop a more severe disease with clinical signs of
pneumonia, such as a high fever (104 deg F to 106 deg F) and increased
respiratory rate and effort. Thoracic radiographs may show consolidation
of lung lobes. Dogs with pneumonia often have a secondary bacterial
infection and have responded best to a combination of broad-spectrum,
bactericidal antibiotics and maintenance of hydration with intravenous
fluid therapy.
Fatality Rate
Fatal cases of pneumonia have been documented, but the
fatality rate so far is low, at 1 percent to 5 percent.
Incubation
The incubation period is two to five days after exposure
before clinical signs appear. Infected dogs may shed virus for seven
to 10 days from the initial day of clinical signs. Nearly 20 percent
of infected dogs will not display clinical signs and become the
silent shedders and spreaders of the infection.
Diagnosis
Current diagnostic tests rely on detection of antibodies
to canine influenza virus, which are detected as early as seven
days after onset of clinical signs. Paired acute and convalescent
serum samples are necessary for diagnosis of recent infection. The
convalescent sample is collected at least two weeks after the acute
sample. There are many situations in which collection of an acute
sample is not feasible. In this case, testing of a convalescent
sample will indicate whether the dog was infected at some time in
the past. Serology tests not only indicate if a dog was infected,
but also serve to alert veterinarians that the virus is present
in their community so they can take precautions with dogs presenting
for “kennel cough.”
In addition to serology, the lungs and distal trachea from dogs
that died of pneumonia can be tested for influenza virus by PCR
analysis and virus culture.
Prevention
There is no vaccine for canine influenza virus at this
time. This virus is spread by aerosolized respiratory secretions,
contaminated inanimate objects and even by people moving back and
forth between infected and uninfected dogs. This is an enveloped
virus that is most likely killed by routine disinfectants, such
as quaternary ammoniums and 10 percent bleach. Because the virus
is highly contagious and all dogs are susceptible to infection,
veterinarians, boarding facilities, shelters and pet stores should
use isolation protocols for dogs that have a “kennel cough.”
Information from the University
of Florida College of Veterinary Medicine
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