A 2015 outbreak of Getah virus infection occurring among Japanese racehorses sequentially to an outbreak in 2014 at the same site

Abstract

BackgroundAs we reported previously, Getah virus infection occurred in horses at the Miho training center of the Japan Racing Association in 2014. This was the first outbreak after a 31-year absence in Japan. Here, we report a recurrent outbreak of Getah virus infection in 2015, sequential to the 2014 one at the same site, and we summarize its epizootiological aspects to estimate the risk of further outbreaks in upcoming years.ResultsThe outbreak occurred from mid-August to late October 2015, affecting 30 racehorses with a prevalence of 1.5 % of the whole population (1992 horses). Twenty-seven (90.0 %) of the 30 affected horses were 2-year-olds, and the prevalence in 2-year-olds (27/613 [4.4 %]) was significantly higher than that in horses aged 3 years or older (3/1379 [0.2 %], P < 0.01). Therefore, the horses newly introduced from other areas at this age were susceptible, whereas most horses aged 3 years or older, which had experienced the previous outbreak in 2014, were resistant. Among the 2-year-olds, the prevalence in horses that had been vaccinated once (10/45 [22.2 %]) was significantly higher than that in horses vaccinated twice or more (17/568 [3.0 %], P < 0.01). Horse anti-sera raised against an isolate in 2014 neutralized both the homologous strain and a 2015 isolate at almost the same titers (256 to 512), suggesting that these viruses were antigenically similar. Among horses entering the training center from private surrounding farms in 2015, the seropositivity rate to Getah virus increased gradually (11.8 % in August, 21.7 % in September, and 34.9 % in October). Thus, increased virus exposure due to the regional epizootic probably allowed the virus to spread in the center, similarly to the outbreak in 2014.ConclusionsThe 2015 outbreak was caused by a virus which was antigenically close to the 2014 isolate, affecting mostly 2-year-old susceptible horses under epizootiological circumstances similar to those in 2014. The existence of 2-year-olds introduced from regions free from Getah virus could continue to pose a potential risk of additional outbreaks in upcoming years. Vaccination on private farms and breeding farms would help to minimize the risk of outbreaks.

Serological Survey of Getah Virus in Domestic Animals in Yunnan Province, China

“…Several GETV outbreaks have occurred in horses and swine in Japan (Bannai et al 2016), India (Broen and Timoney 1998), and China (Yang et al 2018). The results of this study revealed that there is a high titer of the GETV neutralizing antibody in many domestic animals in Yunnan Province, which suggests that GETV may cause infections in domestic animals in the local area.…”

“…In 1978, the first outbreak of GETV infection in horses was reported in Japan, and nearly 40% of the local horse population became infected. In 2012, prevalent GETV infection in horses occurred again in Japan (Bannai et al 2016). In the 1990s, an outbreak of GETV occurred among horses in India, and the associated morbidity reached 30% (Broen and Timoney 1998).…”

An outbreak of Getah virus infection among pigs in China, 2017

“…The first epizootic GETV infection occurred among racehorses in Japan in 1978 (Kamada et al., ). Subsequently, outbreaks of GETV infection have occurred among horses in 1979, 1983, 2014 and 2015 in Japan (Bannai et al., ; Nemoto et al., ; Sentsui & Kono, ; Sugiura et al., ) and in 1990 in India (Brown & Timoney, ). In pigs, sporadic cases of GETV infection were reported in the 1980s in Japan (Shibata, Hatano, Nishimura, Suzuki, & Inaba, ; Yago, Hagiwara, Kawamura, & Narita, ); a recent seroepizootiologic investigation found GETV circulating in south Ibaraki and north Chiba in Japan, and this circulation was concomitant with the outbreaks in racehorses (Bannai et al., ).…”

Endemic and Emerging Arboviruses in Domestic Ruminants in East Asia

“…The prevalence of GETV has been confirmed in mainland China, Japan, Korea, and Taiwan (229,230). Outbreaks of GETV infection have occurred among Japanese racehorses (231,232). It is known that GETV also infects cattle, although there is no evidence of illness in the infected cattle (226,233,234).…”