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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