Introduction
Canine influenza, sometimes called the “dog flu,” is a highly contagious disease caused by a relatively recent adaptation of an equine influenza virus to the canine species. The Canine Influenza Virus (CIV) was identified and classified following an unusual outbreak of respiratory disease in racing greyhounds that occurred in Florida in early 2004. Fortunately, with extensive research directed toward this disease, there now are a number of diagnostic tools available to canine veterinarians.
Diagnosis of Canine Influenza
Once veterinarians realized that a canine influenza outbreak was occurring, there was a rush to isolate the virus in order to find a way to test for - and vaccinate for - the disease. Canine influenza cannot be diagnosed based upon clinical signs alone, because the signs of this disease are virtually identical to those caused by other respiratory pathogens. Technology has progressed to the point where antibodies to CIV can be identified in blood samples after the first week of clinical disease, using what is called a serum hemagglutination inhibition test. While this was a significant improvement over only post-mortem diagnosis, it still required waiting 7 days and prolonged the start of effective treatment.
Newer technology now exists to assist in the diagnosis of influenza in dogs. Called “polymerase chain reaction” technology, or “PCR”, it involves identification of viral DNA in samples taken of nasal or pharyngeal (throat) respiratory secretions during the first 4 days of infection, using sterile swabs. Identification of the virus itself during this acute phase of infection is also now possible. While these tests are useful if a dog has been ill for fewer than 4 days, the results are less reliable after that time. Moreover, while positive PCR results mean that the dog probably is infected with CIV, negative PCR results may be falsely negative if the swabs were taken before or after the period of peak viral shedding. The most reliable way to diagnosis canine influenza is paired serologic testing on two blood samples – one collected during the first week of clinical illness, and another taken 2-3 weeks later. Of course, over time other diagnostic tools may be developed for this disease.
If your dog shows signs of influenza, contact your veterinarian immediately. Your veterinarian is in the very best position to determine what is causing your dog’s respiratory signs, and how best to treat them.