Methods of increasing the sensitivity of the haemagglutination inhibition test for rabies virus antibody

A new method for the removal of non-specific inhibitors of rabies virus haemagglutinin has been developed. Treatment with colloidal silicic acid (Aerosil) or with acetone plus Aerosil reduced the non-specific inhibitors in human, mouse, and dog sera to a level that was undetectable at the 1:4 starting dilution in the haemagglutination inhibition test.Bromelain-treated goose erythrocytes were much more susceptible to haemagglutination by rabies virus than were untreated erythrocytes, and the sensitivity of the haemagglutination inhibition test was considerably increased by using bromelain-treated erythrocytes. Low levels of antibodies in sera from immunized human subjects were detected with higher sensitivity by combining Aerosil treatment of the sera with the use of bromelain-treated goose erythrocytes in the haemagglutination inhibition test.