Fact Sheet for Veterinarians
WADDL/Washington Dept of Health/WSDA
Canine Influenza Virus Canine influenza was first identified in
January, 2004 when an outbreak occurred among Florida racing
dogs. This virus is of the H3/N8 subtype and is most closely
related to the equine influenza H3/N8 virus. Since the first
identified outbreak, more outbreaks have occurred among racing
dogs as well as in shelter dogs in Florida. There is also
evidence of infections occurring in owned pet dogs, and among
New York State and Massachusetts dogs as well.
Clinical Signs
There are two clinical syndromes: a mild illness characterized
by fever and cough followed by recovery, or peracute death
associated with hemorrhage in the respiratory tract. Because
this is a new pathogen almost all dogs are susceptible to
infection and almost an estimated 80% of exposed dogs develop
clinical signs. Most dogs develop the milder syndrome, involving
a cough that persists for 10 to 21 days despite therapy with
antibiotics and cough suppressants. This syndrome can also
include purulent nasal discharge and a low-grade fever.
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The more severe disease involves pneumonia, including a high
fever (104� to 106� 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 intravenous fluid
therapy.
The case-fatality rate in the initial outbreak was high (8 of 22
ill dogs died, for a 36% case-fatality rate), but since then
case-fatality has been reportedly low (1 to 5%).
Incubation and infectious periods Clinical signs appear two to
five days after exposure. Infected dogs may shed virus for seven
to 10 days from the onset of clinical signs. An estimated 20% of
infected dogs will not show clinical signs and can become
asymptomatic sources of infection for other dogs.
Diagnosis
The diagnosis of canine influenza infection at this time is most
reliably done by detecting antibodies to the virus. Acute and
convalescent sera can be sent to the laboratory for serologic
testing. Canine influenza serology testing at WADDL uses a
screening assay that requires confirmation of all positive
results at another laboratory. Collection of oropharygeal swabs
or tracheal wash samples on febrile dogs early in the course of
the disease may be submitted on ice pack to the laboratory for
virus isolation or detection of viral DNA by polymerase chain
reaction assay (PCR). Tissues (lung, bronchiolar lymph nodes)
from dogs that have died acutely can be submitted to the
laboratory, a portion fixed in buffered formalin, and fresh
tissues submitted on ice pack for bacterial and viral isolation.
Contact WADDL at 509-335-9696 if any questions arise.
Prevention
There is no vaccine against canine influenza and the use of
influenza vaccines approved for other species is contraindicated
because of the potential for adverse and possibly fatal
reactions in dogs. This virus is spread by aerosolized
respiratory secretions and by fomites. Dogs presenting with
respiratory signs should be isolated and surfaces that may have
been contaminated with their respiratory secretions should be
disinfected with bleach or quarternary ammonia compounds.
Veterinarians and their staff should wash hands after examining
and treating dogs with cough, and before touching other,
potentially susceptible animals. Clients should be advised
against kenneling (boarding) coughing dogs, or otherwise
exposing susceptible dogs.
Canine influenza fact sheet, Sept 26, 2005
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