DIAGNOSIS OF EQUINE INFLUENZA BY THE POLYMERASE CHAIN-REACTION

Influenza A is a common respiratory infection of horses, and rapid dia gnosis is important for its detection and control. Sensitive detection of influenza currently requires viral culture and is not always feasi ble. The polymerase chain reaction (PCR) was used to detect DNA produc ed by reverse transcription of equine influenza in stored nasal secret ions, vaccines, and allantoic fluids. Primers directed at a target of 212 bp on conserved segment 7 (matrix gene) of human influenza A/Bangk ok/1/79 (H3N2) produced amplification products of appropriate size wit h influenza A/Equine/Prague/1/56 (H7N7), A/Equine/Miami/63 (H3N8), A/E quine/Kentucky/79 (H3N8), and A/Equine/Kentucky/2/91 (H3N8) in infecte d frozen allantoic fluids and in frozen extracts of nasal swabs of 2 h orses with naturally acquired influenza. The products bound a P-32-lab eled hybridization probe to an inner region of the target. Control sam ples, including nasal secretions from a horse infected with herpesviru s, were negative. In a prospective study, 2 ponies inhaled aerosols of influenza A/Equine/Kentucky/2/91 (H3N8), and thereafter supernatants of nasal swabs in transport medium were obtained daily for 10 days for culture and PCR. Amplification products were evaluated by size and bi nding of a P-32-labeled probe and also by dotblotting and binding of a biotin-labeled probe. Culture detected influenza more consistently th an did PCR in the first 2 days of infection, but PCR detected virus mo re often later in infection. Gels were the most sensitive, but radiome tric and biotin-labeled probes gave specific results and were consiste ntly positive from days 3-6. PCR is suitable for detection of equine i nfluenza in clinical samples.