A definitive diagnosis of canine influenza can be made using laboratory testing, but timing of sample collection is critical and is related to the time of initial exposure and peak viral shedding.
ANCILLARY DIAGNOSTIC WORK-UP FOR INDIVIDUAL DOGS
THE DIAGNOSTIC WORK-UP
This can provide important information 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.40
Serology to detect CIV-specific antibodies is the most reliable diagnostic test for confirmation of canine influenza infection.
This testing should be performed in conjunction with other tests to confirm virus presence.
CIV-specific antibodies can be detected in a hemagglutination inhibition assay as early as 7 days post infection; however, reliable detection occurs after 10 days of clinical signs.40,44
It is important to note that a negative antibody titer for serum samples collected before day 10 does not rule out CIV infection. 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.
Because of increasing prevalence, rapid spread, and the potential for up to 20% of dogs to have a severe disease course, veterinarians should examine further any dogs showing clinical signs.
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, and several methods may be used depending on the stage of infection in the dog.40Dog Flu Sampling Procedures
Dr. Natalie Marks covers procedures and best practices for sampling and testing.
Nasal and/or caudal pharyngeal swabs can also be used for detection of CIV nucleic acid by PCR tests.40 PCR testing is fast and inexpensive, and is now offered by several reference and university diagnostic laboratories.
In addition, PCR tests have high sensitivity and specificity, and are more likely to show positive results when there are low levels of virus present, such as in later stages of infection.
False-negative results can occur if the timing of sample collection is not appropriate.
SUMMARY OF DIAGNOSTIC TESTING OPTIONS FOR CANINE INFLUENZA
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40. Crawford C, Spindel M. Canine influenza. In: Miller L, Hurley K, eds. Infectious Disease Management in Animal Shelters. Ames, IA: Wiley-Blackwell; 2009:173-180.
44. Anderson TC, Katz JM, Gibbs EPJ, Crawford PC. Development of a hemagglutination inhibition assay for diagnosis of canine influenza virus infection. Paper presented at: 110th Annual Meeting USAHA and 49th Annual Conference of the American Association of Veterinary Laboratory Diagnosticians; October 12-18, 2006; Minneapolis, MN.
76. Syndromic surveillance data of Cynda Crawford, DVM, PhD, University of Florida; Edward Dubovi, PhD, Cornell University; Sanjay Kapill, DVM, PhD, ACVIM, Oklahoma State University; and IDEXX Laboratories. August 2018.