Several laboratory tests are available to detect outbreaks of canine influenza.
CIV infection should be suspected in dogs with respiratory signs.
Swabs for Immunoassays, PCR, and Virus Isolation
An early diagnosis of canine influenza is challenging because initial clinical signs are usually mild or even inapparent. However, it is during this timeframe that viral shedding in nasal secretions is highest and diagnostic testing aimed at identifying the virus is most accurate. In addition, it is during this time that establishing a diagnosis of CIV as the cause of an outbreak is critical for optimal outbreak control and case management.2
In early cases, diagnostic methods aimed at detection of the virus are preferred, including antigen detection methods, polymerase chain reaction (PCR)-based assays, and virus isolation. Nasal and/or caudal pharyngeal swabs are used for these tests. Optimally, swabs should be collected from dogs with early clinical signs (1 to 3 days) to coincide with peak virus shedding. In kennel or shelter populations, these swabs can be taken from exposed dogs; in this case, it is best to take swabs from multiple dogs in the population.2
Immunoassay kits for detection of human influenza A infection can be used for diagnosis of canine influenza because they detect the highly conserved nucleoprotein of influenza A viruses. However, the sensitivity for CIV is unknown. Advantages are that these kits do not require special equipment, are easy to perform, and provide rapid results. Limitations are that, while the kits are likely to provide positive results correctly, they can also report false-negative results based on the timing of peak viral shedding.2
Nasal and/or caudal pharyngeal swabs can also be used for detection of CIV nucleic acid by PCR tests.2 Advantages of PCR testing are that it 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 CIV infection, than virus antigen immunoassays. However, the high sensitivity can lead to false-positive results if there is DNA contamination during sample collection, or during processing in the lab. To avoid contamination during swab collection, the person collecting the sample should wear clean examination gloves for each dog and only touch the swab tip to the area sampled to avoid contamination by DNA on hands and in the environment. False-negative results can occur if the timing of sample collection is not appropriate. Of note, PCR testing can also be performed on other biological samples, such as transtracheal washes, bronchoalveolar lavage fluid, and tissues.2
PCR testing is performed at numerous locations, including the following centers:4
- Cornell University College of Veterinary Medicine Animal Health Diagnostic Center
- University of California, Davis, School of Veterinary Medicine
- The Lucy Whittier Molecular & Diagnostic Core Facility
It is important to note that these laboratories should be contacted in advance to determine collection, handling, and shipping preferences.
Virus isolation has limited use for routine diagnostic testing because it is specialized and slow to perform. It is most appropriately used for epidemiologic investigation and future vaccine production.