Capacity of certain Echo virus 6 strains to cause hemagglutination

Echo 6 strains propagated in amnion cell cultures have been found capable of agglutinating human erythrocytes. About 10 6–10 7 ID 50 of virus per milliliter are required to produce hemagglutination. The prototype 6 strain, D'Amori, does not cause hemagglutination even at high titer. The agglutination takes place at different temperatures, but maximal titers are obtained at 37°. There is a pH dependence, the optimal pH range being around pH 7.0. The hemagglutinating strains are adsorbed onto the red cells whereas adsorption of the D'Amori strain is less significant. Echo 6 antisera suitable for serologic work can be obtained by immunization of rabbits. The antisera inhibit specifically the hemagglutination. A small number of paired sera from patients with aseptic meningitis have been tested, and there is indication that the hemagglutination inhibition may be of value in diagnostic work.