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This study was designed to investigate 1) the role of Black-crowned Night Herons (BCNH) in the dissemination of Japanese encephalitis virus, 2) to investigate the mosquito vectors that participate in the annual epidemic, and 3) to determine the chronology of infection in Herons, mosquitoes, and man in the area of a heronry in Taiwan during 1967 and 1968. Nestling BCNH and sentinel pigs were serially bled to determine the time of development of antibody. Mosquitoes were collected from light traps, pig-baited and birdbaited Magoon traps, and by hand from pigs. Cases in man were serologically confirmed. Although the arrival of the Herons and the prevalence of mosquitoes paralleled previous years, the epidemic was 2 months later than usual. Infection was found first in pigs in late July, then in man and Herons, and last in mosquitoes in mid-August. Culex annulus (Theobald) was the most prevalent mosquito and the source of three of the five pools yielding virus. The results suggest that C. annulus (Theobald) is the principal mosquito vector of Japanese encephalitis virus, and that BCNH did not bring the virus to Taiwan. However, the sequence of infection suggests that mosquitoes thus far implicated were not the initial vector. Thus this study raises the question of undetermined insect and animal vectors in the dissemination of JE virus.
Present address: Epidemiology Branch, National Institute of Neurological Diseases and Stroke, National Institutes of Health, Bethesda, Maryland 20014.
Present address: Western Field Research Laboratory, Chevron Chemical, Fresno, California 93705.
U.S. Naval Medical Research Unit No. 2, APO San Francisco 96263.