Canine influenza or
dog flu is
influenza occurring in
canines. Canine influenza is caused by varieties of
Influenzavirus A, such as
equine influenza virus
H3N8, which in 2004 was
discovered to cause disease in dogs. Because of the lack of
previous exposure to this virus, dogs have no natural
immunity to this virus. Therefore, the
disease is rapidly transmitted between individual dogs.
Canine
influenza may be endemic in
some regional dog populations of the United States
. It is a disease with a high
morbidity but a low
mortality.
History
The highly
contagious equine influenza A virus subtype H3N8 was found to have
been the cause of Greyhound race dog fatalities from a respiratory illness at a Florida
racetrack in
January 2004. The exposure and transfer apparently occurred
at
horse racing tracks, where
dog racing also occurs. This was the first
evidence of an influenza A virus causing disease in dogs. However,
serum collected from racing Greyhounds
between 1984 and 2004 and tested for canine influenza virus (CIV)
in 2007 had positive tests going as far back as 1999. It is
possible that CIV caused some of the respiratory disease outbreaks
at tracks between 1999 and 2003.
H3N8 was
also responsible for a major dog flu outbreak in New York
state in all
breeds of dogs. From January to May 2005, outbreaks occurred
at 20 racetracks in 10 states (Arizona
, Arkansas
, Colorado
, Florida,
Iowa
, Kansas
, Massachusetts
, Rhode
Island
, Texas
, and
West
Virginia
). As
of August 2006, dog flu has been confirmed in 22 U.S. states,
including pet dogs in Wyoming, California, Connecticut, Delaware,
and Hawaii. There are three areas in the United States that may now
be considered endemic for CIV due to continuous waves of cases: New
York, southern Florida, and northern Colorado/southern Wyoming.
There is no evidence that the virus can be transferred to people,
horses, cats, or other species.
H5N1 (avian influenza)
was also shown to cause death in one dog in Thailand
, following ingestion of an infected duck.
The virus
Influenza A viruses are
enveloped
negative sense
single-stranded
RNA viruses. Genome
analysis has shown that H3N8 was transferred from horses to dogs
and then adapted to dogs through
point
mutations in the
genes. The
incubation period is two to five days and
viral shedding may occur for seven to
ten days following the onset of symptoms. It does not induce a
persistent
carrier state.
Symptoms
About 80 percent of infected dogs with H3N8 show symptoms, usually
mild (the other 20 percent have
subclinical infections), and the
fatality rate for Greyhounds in early outbreaks was 5 to 8 percent,
although the overall fatality rate in the general pet and shelter
population is probably less than 1 percent. Symptoms of the mild
form include a cough that lasts for ten to thirty days and possibly
a greenish nasal discharge. Dogs with the more severe form may have
a high fever and
pneumonia. Pneumonia in
these dogs is not caused by the influenza virus, but by secondary
bacterial infections. The fatality rate of
dogs that develop pneumonia secondary to canine influenza can reach
50 percent if not given proper treatment.
Necropsies in dogs that die from the disease reveal
severe
hemorrhagic pneumonia and evidence
of
vasculitis.
Diagnosis
The presence of an upper respiratory tract infection in a dog that
has been vaccinated for the other major causes of
kennel cough increases suspicion of infection
with canine influenza, especially in areas where the disease has
been documented. A
serum sample from a
dog suspected of having canine influenza can be submitted to a
laboratory that performs
PCR tests for this virus.
Vaccine
In June
2009, the United States Department of
Agriculture
(USDA) Animal and Plant
Health Inspection Service (APHIS) approved the first canine
influenza vaccine.
See also
References
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