Issue Description 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. Other Names CIV
History The highly contagious equine influenza virus
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.
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.
Treatment and Prevention Treatment is generally supportive care and
antibiotics for secondary bacterial infections. The virus is easily
inactivated with common disinfectants such as bleach solutions and
quaternary ammonium compounds. There is no vaccine available at this
time, but there has been investigation of a canarypox-vectored vaccine
for equine influenza virus for use in dogs.