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. 2016 Jun 10;12:98.
doi: 10.1186/s12917-016-0741-5.

A 2015 Outbreak of Getah Virus Infection Occurring Among Japanese Racehorses Sequentially to an Outbreak in 2014 at the Same Site

Free PMC article

A 2015 Outbreak of Getah Virus Infection Occurring Among Japanese Racehorses Sequentially to an Outbreak in 2014 at the Same Site

Hiroshi Bannai et al. BMC Vet Res. .
Free PMC article


Background: As 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.

Results: The 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.

Conclusions: The 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.

Keywords: Getah virus; Japan; Racehorses; Sequential outbreak.


Fig. 1
Fig. 1
Numbers of pyretic horses and Getah virus–infected horses at the Miho training center. Bars indicated the number of pyretic horses each week from 1 June to 15 November. Black, number of horses positive on RT-PCR for Getah virus or seroconverted to Getah virus on VN testing, or both
Fig. 2
Fig. 2
Rates of seropositivity to Getah virus in horses transferred from farms surrounding the Miho training center. Sera were collected from horses introduced to the Miho training center between June to October in 2014 or 2015. The horses (n = 51 to 81 in each month) were 2-year-olds that had been transferred from Ibaraki or Chiba prefecture and had no history of Getah virus vaccination. Sera were subjected to VN testing using the 14-I-605 strain. Data for 2014 are quoted from our previous report [6]

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