Comparative sensitivity of counterimmunoelectrophoresis and double immunodiffusion tests for identification of influenza A viruses in birds isolates.

Fifty cloacal swab specimens which were found positive by haemagglutination after one or two passages in chicken embryonated eggs were examined for the presence of influenza A virus by counterimmunoelectrophoresis (CIE) and double immunodiffusion (DID) with anti-matrix and anti-nucleoprotein sera. CIE was as sensitive as DID with the anti-nucleoprotein serum and more sensitive with the anti-matrix serum when virus from allantoic fluid was concentrated with acid and disrupted with the detergent Sarcosyl. However, when the concentration step was by-passed and the virus was disrupted with Sarcosyl alone, CIE was substantially more sensitive. Forty-nine samples were positive for type A influenza with the anti-matrix serum and 37 with the anti-nucleoprotein serum. By DID, only 16 could be identified with the anti-matrix serum and none could be typed with the anti-nucleoprotein serum. Since CIE with anti-matrix serum is more sensitive than the DID tests, even with unconcentrated infected allantoic fluid, the CIE test is preferred for large-scale identification of influenze A virus in bird isolates.