Complete Genome Sequencing and Phylogenetic Analysis of a Getah Virus Strain (GenusAlphavirus, FamilyTogaviridae) Isolated fromCulex tritaeniorhynchusMosquitoes in Nagasaki, Japan in 2012

Abstract

Getah virus (GETV; genus Alphavirus, family Togaviridae) is a mosquito-borne virus known to cause disease in horses and pigs. In 2014, for the first time in ∼30 years, a sudden GETV outbreak occurred among racehorses in Ibaraki, Japan. Two years before this outbreak, we obtained multiple GETV isolates from Culex tritaeniorhynchus mosquitoes collected in Nagasaki, Japan and determined the whole genome sequence of GETV isolate 12IH26. Our phylogenetic analysis of GETV strains revealed that the isolate 12IH26 forms a robust clade with the epidemic strains 14-I-605-C1 and 14-I-605-C2 isolated from horses in the 2014 outbreak in Ibaraki. Furthermore, the complete genomic sequence of the isolate 12IH26 was 99.9% identical to those of the 2014 epidemic strains in Ibaraki. Phylogenetic analysis also showed that the recent Japanese GETV strains, including the isolate 12IH26, are closely related to the Chinese and South Korean strains rather than the previous Japanese strains, suggesting that GETV strains may be transported from overseas into Japan through long-distance migration of the infected mosquitoes or migratory birds.

Deciphering the Virome of Culex vishnui Subgroup Mosquitoes, the Major Vectors of Japanese Encephalitis, in Japan

“…The phenomenon of this virus spread has also occurred in Getah virus (genus Alphavirus, family Togaviridae). A study reported the virus being transported in the same direction from west Japan into central Japan, with possible routes of transportation, such as bird migration and windblown mosquitoes [56].…”

Geospatial and temporal associations of Getah virus circulation among pigs and horses around the perimeter of outbreaks in Japanese racehorses in 2014 and 2015

“…Phylogenetic analysis showed that strain 15-I-1105 was located in the same cluster as the strains isolated from horses during the 2014 outbreak (14-I-605-C1, 14-I-605-C2), one strain isolated from a horse during the 2015 outbreak (15-I-752), and one strain isolated from mosquitoes in Nagasaki Prefecture in 2012 (12IH26, [14]) (Fig. 2).…”

“…Our phylogenetic analysis of various Getah virus strains revealed that the strain from a pig (15-I-1105) and strains from recent outbreaks in horses (14-I-605-C1, 14-I-605-C2, and 15-I-752) formed a cluster with a strain isolated from mosquitoes in Nagasaki Prefecture in 2012 (12IH26, [14]) (Fig. 2).…”

“…2). Phylogenetic analyses by Kobayashi et al using the sequences for the E2 , capsid , and nsP1 genes suggested that this cluster containing 12IH26, 14-I-605-C1, and 14-I-605-C2 was closely related to the recent Chinese and South Korean strains but only distantly related to Japanese strains from the 1970s and 1980s [14]. Although it is still unclear how and when the virus was brought into Japan from overseas and spread into Ibaraki and Chiba prefectures, this cluster of viruses seems to have been established in these areas and was circulating among both pigs and horses in recent years.…”

Complete Genome Sequences of Getah Virus Strains Isolated from Horses in 2016 in Japan

“…An epidemic occurred at the same location in 2016. In addition, Getah viruses were isolated from mosquitoes in 2012 ( 7 ) and pigs in 2015 ( 8 ). Here, we read the complete genome sequences of the strains isolated from horses in 2016 and compared them with those of the strains recently isolated from horses, pigs, and mosquitoes.…”