Fig. 1.

Locations of the study areas. The area in the southern part of Ibaraki Prefecture (south Ibaraki, gray) includes the village of Miho and the cities of Inashiki, Ushiku, and Tsuchiura and covers an area of 454 km². There are 27 pig farms rearing about 32,000 pigs. The area in the northern part of Chiba Prefecture (north Chiba, black) includes the towns of Tako and Tohnosho and the cities of Inzai, Katori, Sakura, Narita, Shiroi, Yachimata, and Tomisato and covers an area of 988 km². There are 158 pig farms rearing about 230,000 pigs. The location of the Miho training center—the site of the outbreak of Getah virus in racehorses in 2014 and 2015—is indicated by the black square