Faced with a coughing dog, a veterinarian will perform a complete physical exam. In a dog with the flu, the exam will reveal findings consistent with influenza, but it won’t reveal an influenza diagnosis.
"The signs of CIV are clinically indistinguishable from those caused by other respiratory pathogens," says Dr. Landolt.
Various tests can help identify influenza, and they follow two main approaches: looking for the CIV virus in respiratory secretions (from the nose or throat) and looking for anti-CIV antibodies in the blood [source: Landolt]. The immune system produces specific antibodies to fight off specific infections.
Timing is often critical in testing. A nasal-swab test is only accurate at the beginning of the illness, because the virus is only reliably present in nasal secretions for about four days after symptoms begin [source: VCA]. And blood tests for antibodies are only reliable later in the illness.
"The body needs several days or even weeks to produce the antibodies in response to infection," explains Landolt.
Both of these methods require collecting samples and sending them to a diagnostic laboratory, so they don't provide immediate results. A veterinarian might decide to run a rapid, "on-site" test, or immunoassay, to support a possible flu diagnosis, which reliably detects components of human influenza A in human respiratory secretions. The test is not as reliable in dogs, though [source: Landolt].
The point of all this is to establish an influenza diagnosis in a sick dog, which is important. It can signal the start of an outbreak in the area. It can help to stop the spread by letting the owner know to keep the dog isolated. And according to Landolt, it can help infectious-disease authorities keep tabs on the virus:
Getting specimens to the lab for testing allows for monitoring of the virus in terms of its genetic and antigenic makeup. While there is no evidence at this time that CIV can transmit to humans ... it is possible that at some time in the future the virus might acquire the capability to infect other species.
But in terms of determining treatment, a definitive influenza diagnosis is not essential.