The Department of Microbiology, University of Minnesota, The Department of Virus and Rickettsial Diseases, 406th Medical General Laboratory, U. S. Army, Walter Reed Army Institute of Research, Minneapolis, Minnesota, Japan
Sagiyama virus is an arthropod-borne virus recovered from mosquitoes collected during July and August 1956 and 1957 near Tokyo, Japan. It is in antigenic group A and thus represents the first isolation in Japan of a group A arthropod-borne virus. It is closely related antigenically to two viruses recovered from mosquitoes in Malaya, apparently possessing an antigen in common with one virus and a different antigen in common with the other virus.
The ecology of Sagiyama virus near Tokyo during the 3 years 1956 to 1958 involved two mosquito species, (Culex tritaeniorhynchus and Aedes vexans), swine, herons, horses, and man. Virus appeared in nature in adult female mosquitoes during July and persisted until September. Presumably it cycled between vector mosquitoes and amplifying vertebrates (pigs, horses, herons, and perhaps other domestic animals and wild birds) until the density of transmitting mosquitoes became great enough to effect dissemination of virus to man. Adult humans living on farms near infected pigs showed an N antibody prevalence of .18 and the overall N antibody prevalence in urban and rural humans during 1956 and spring 1957 was .09. Eventually virus disappeared as mosquito breeding ceased and as mosquitoes disappeared in September, and like JE virus, the overwintering mechanism of Sagiyama virus is as yet unknown. The existence of N antibody in serum of a horse and a human in May and early June 1956 before the summer mosquito season provided evidence that Sagiyama virus or at least a closely related virus existed near Tokyo before the virus was first isolated in July 1956.
Although Sagiyama virus coexisted with JE virus in certain habitats and even dual infections occurred in swine, the two viruses were not interdependent nor were they mutually exclusive. In the habitats studied near Tokyo, their ecologies were similar except that Sagiyama virus involved Aedes vexans, a mosquito not found infected by JE virus during the years of these studies, and JE virus was much more widely disseminated among Culex tritaeniorhynchus, pigs, herons, and man than was Sagiyama virus.