“…Passive hemagglutination [7] was performed by using macro-or microtiter plates (Medpolymer, Leningrad) and antigen-coated erythrocytes (0:4, 12, 0 : 9,12, 0 : 3,10) either obtained from the G.N. Gabrichevsky Institute of Epidemiology (Moscow) or prepared in the authors' Institute using sheep erythrocytes treated with formalin [8] and tannic acid (Merck) [9].…”