Fig. 1.

Spatial distribution of pigs in Vietnam and the geographical locations of pig farms in northern Vietnam. a Pig density is illustrated by deepening shades of green, indicating category level; square indicates the study area. b Digital elevation model of the location of pig farms in northern Vietnam. A total of 6601 samples were collected on 327 pig farms located in 19 provinces in northern Vietnam from January 2018 to February 2019. Red dots indicate PEDV-positive farms and blue dots indicate PEDV-negative farms