Ecologic Studies of Japanese Encephalitis Virus in Japan

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Abstract
Summary Certain characteristics of ardeids and their behavior were important in the ecology of JE virus at heronries near Tokyo, Japan. No species of ardeid was innately immune to JE virus but, following infection, birds developed immunity which probably reduced the size of the susceptible bird population. Up to 67% of newly-hatched birds possessed passively-acquired, maternal, neutralizing antibody which subsequently disappeared. Although this antibody could temporarily delay infection of nestlings, it probably did not significantly reduce the total seasonal amount of JE virus available in ardeids for infection of vector mosquitoes. Breeding habits governed the supply of susceptible nestlings which, when viremic, serve as sources of virus for vector mosquitoes. Anatomical features, nest habitats and flight habits of adults influenced exposure of nestlings to mosquitoes. Flight activities and feeding habits made possible the introduction of virus into heronries from without, either by viremic birds or by unknown mechanisms; for example, tissue invading endoparasites. Migration and dispersal of birds during August–November provided possible means of spreading virus beyond the colonies.