Canine respiratory PCR (adenovirus CAV-2, canine influenza, Bordetella)

What it shows

PCR finds DNA or RNA of a specific agent. A form may show three lines from a respiratory panel:

• Canine adenovirus (CAV) PCR — canine adenovirus type 2 (CAV-2), one of the viruses involved in kennel cough.
• Canine influenza virus (CIV) PCR, H3N2/H3N8 — the two known strains of dog flu. H3N8 came from horse influenza and was first identified in the USA in 2004; H3N2 came from bird influenza. A general influenza A test detects both; some labs then confirm the strain.
• Bordetella bronchiseptica PCR — a bacterium that can cause disease on its own, especially in dogs under 6 months, and often occurs with viruses.

Panels often include other agents too, such as canine parainfluenza virus, distemper virus and canine respiratory coronavirus. Mixed infections, most often Bordetella with parainfluenza and CAV-2, are common.

Higher than reference — what it may be a sign of

• “Detected” — the agent’s genetic material is in the sample. In a coughing dog this supports its role, but PCR finds genetic material, not necessarily active disease.
• Recent vaccination — in a small study of 8 puppies vaccinated with, among others, an intranasal live vaccine, PCR repeatedly detected CAV-2, Bordetella and parainfluenza for up to 28 days, most often on days 3–10. The authors advise taking vaccination status into account when reading these results.
• Canine influenza — a positive PCR in a dog with fitting signs supports dog flu. About 80% of exposed dogs have a mild illness with a cough lasting 1–3 weeks; about 20% have no signs but can still shed the virus.

The vet weighs the result together with the signs, vaccination dates and, when needed, X-rays, and decides on the next steps.

Lower than reference

“Not detected” does not rule out a respiratory infection. Timing matters: for canine influenza, swabs from dogs ill for less than 3 days are best, and after 4 days of illness PCR can be falsely negative because peak shedding has passed. Then a pair of blood samples for antibodies, taken some weeks apart, is the best way to confirm flu. A negative result may also mean that another agent, not on this part of the panel, causes the cough.

Look at together with

• Other agents on the panel — for example distemper virus, which can also cause respiratory signs.
• Bordetella culture — some labs grow the bacterium from a separate swab taken from the same site.
• Chest X-rays — show whether the lungs are involved.
• Vaccination record — the type and date of the last kennel cough vaccine matter for reading the PCR.

Units and conversion

All three results are qualitative and have no unit. They are reported as “detected” or “not detected” (sometimes “positive” / “negative”). For influenza, the form may also name the strain, H3N2 or H3N8. In the app these results are stored as text, as printed on the form.

Reference range

The reference range is on your lab’s form; for PCR it is “not detected”. A result is read together with the signs, the day of illness when the swab was taken and recent vaccinations.

Cats and dogs

Sources

1. Merck Veterinary Manual — Kennel cough
2. Merck Veterinary Manual — Canine influenza (flu)
3. Ruch-Gallie R, Moroff S, Lappin MR. Adenovirus 2, Bordetella bronchiseptica, and parainfluenza molecular diagnostic assay results in puppies after vaccination with modified live vaccines (J Vet Intern Med, 2016)
4. ABCD (European Advisory Board on Cat Diseases) — Guideline for Bordetella bronchiseptica infection in cats
5. Antech Diagnostics — Respiratory PCR panel (canine)