A simple double immunodiffusion test for typing influenza viruses.

The identification of influenza virus type has traditionally been based on the characterization of internal nucleoprotein (NP) antigens by the complement fixation (CF) test. Because this test is complex and time-consuming, it is used only infrequently. In this report we describe a double immunodiffusion (DID) test, which is proposed as a replacement for the CF test for the typing of influenza viruses. The DID test is simple and requires only the allantoic fluid content of a single infected embryonated egg. Virus from the infected fluid is precipitated with mild acid and disrupted by detergent. Anti-NP or anti-matrix protein (MP) antibody is equally effective in most instances for typing influenza isolates by this test. The latter is preferred, however, since it seemed to be slightly more sensitive than anti-NP antibody.