Immunologic studies of Japanese encephalitis virus in Japan. III. Infection and antibody responses of birds.

Neutralizing and HI, but not CF antibodies, were found in plasma of previously viremic birds when tested for 8–12 weeks after infection. Antibodies formed in some birds that failed to circulate virus. HI antibody appeared promptly within 2–3 days of cessation of viremia and reached maximal titers within 14–21 days following infection. Neutralizing antibody did not appear until the 3rd–12th postinfection weeks and an occasional bird never produced significant levels of neutralizing antibody during the 3 months after development of viremia and HI antibody. The titer of HI antibody usually decreased during the second and third postinfection months but neutralizing antibody persisted longer. Occasionally both antibodies became undetectable between 3 and 9 months after infection.