Understand the Methods to Diagnose Dog Flu
Dog Flu should be suspected in dogs with respiratory signs.
Because of the increasing prevalence of Dog Flu (canine influenza), the rapid spread of the infection among dogs, and the potential for up to 20% of dogs to have a severe disease course, veterinarians and other pet care professionals should examine further any dogs with cough, nasal discharge or fever. Dog Flu infection should be suspected in dogs with persistent cough and those with pneumonia or other clinical signs of more severe respiratory illness.6
It is important for diagnostic tests to be performed to determine the cause of canine cough outbreaks because Dog Flu symptoms can sometimes seem like other respiratory infections.2
A clinic can use multiple methods to test for both strains (CIV H3N8 and CIV H3N2).
Each of these tests can help with different readings. Several methods may be used on one dog because results can vary depending on the stage of infection of Dog Flu in the dog.2
A veterinarian should be contacted for guidance on appropriate testing, as well as isolation precautions and treatment.6 Remember that a positive test for other respiratory infections does not rule out Dog Flu, since secondary infections are common.2,6,8,12
Summary of Diagnostic Testing Options for Dog Flu.2,6,8,12
|Diagnostic test: Flu Antigen ELISA
||Description: BD Directigen™ Flu A Test Kit Quidel Quickvue® What: Human influenza A test that can be used for Dog Flu How: Obtain nasal and/or pharyngeal swabs from dogs within 4 days of clinical signs onset Results: False negatives uncommon
|Diagnostic test: Serology
||Description: How: Obtain samples one week after onset of signs, and a second sample 2-3 weeks later Results: Can indicate a recent infection or past exposure in a dog without canine vaccinations
|Diagnostic test: PCR
||Description: IDEXX real-time PCR panels How: Most sensitive before onset of signs in recently exposed dogs Results: False negatives common after onset of signs
|Diagnostic test: Virus Isolation
||Description: How: Collect nasal swabs as early as possible, before antibodies develop, in order to track genetic changes in virus as it spreads through the dog population Results: Relatively unreliable way to confirm infection due to timing of sample collection
Ancillary Diagnostic Work-up for Individual Dogs
The diagnostic work-up for individual dogs with suspected or confirmed Dog Flu can provide important information to assist veterinarians in making treatment decisions.
- A complete blood count (CBC) with differential, serum biochemistry profile, urinalysis, thoracic radiographs, and cultures can all provide helpful information. The CBC may be normal, or show mild leukopenia consistent with viral infection; however, leukocytosis (neutrophilia) with or without a left shift may indicate that the dog is developing pneumonia.
- Thoracic radiograph findings may range from mild bronchointerstitial infiltrates to consolidation of all lung lobes.
- Secondary bacterial infection may be identified by cultures performed on nasal swabs from dogs with purulent nasal discharge, or on transtracheal and endotracheal washes of dogs with pneumonia. Potential pathogens include a variety of gram-positive and gram-negative bacteria, including Staphylococcus spp., hemolytic and nonhemolytic Streptococcus spp., Pasteurella multocida, Klebsiella pneumoniae, Escherichia coli, and Mycoplasma spp.
- Antibiotic therapy can be targeted based on culture and sensitivity results.2
Serology to detect CIV-specific antibodies is the most reliable diagnostic test for confirmation of Dog Flu infection.
- This testing should be performed in conjunction with other tests to confirm Dog Flu.
- The timing of serum sample collection is also critical. CIV-specific antibodies can be detected in a hemagglutination inhibition assay as early as 7 days postinfection; however, reliable detection occurs after 10 days of clinical signs.2,24
It is important to note that a negative antibody titer for serum samples collected before day 10 does not rule out CIV infection.2,4 In addition, because the presence of antibodies only indicates exposure but not necessarily active infection, it is necessary to compare an acute titer with a titer taken at least 2 weeks later (a convalescent titer) to confirm a four-fold or greater rise in antibody titer (seroconversion) in order to prove that there was a recent active infection.2,4