Epidemiological factors associated to spread of porcine epidemic diarrhea in Japan

Porcine epidemic diarrhea (PED) is an emerging disease of pigs that has recently led to large numbers of piglet deaths in a number of countries of Eastern Asia and The Americas. The objective of the present study was to identify and compare risk factors associated with PED infection in locally and non-locally PED-exposed farms in Japan. A questionnaire was administered to a convenience selection of pig farms located throughout Japan. Questionnaires were administered between November 2013 (when the first case was reported in Japan) and August 2014. PED-positive farms (cases, n = 124) were asked to provide information on their status (positive or negative) and select herd management practices for the two weeks prior to onset of PED clinical signs. Negative farms (controls, n = 128) were given the same questionnaire and asked herd management practices for the two weeks prior to a given reference date. This date was assigned based on the date of PED occurrence in the town/prefecture in which the farm was located. Case and control farms were categorized as "locally exposed" if they were located within a 5 km radius from a PED-infected farm and "non-locally exposed", otherwise. Logistic regression analysis was used to identify factors associated with PED infection. Two separate regressions were done for locally exposed and non-locally exposed farms using PED status (positive/negative) as the dependent variable. PED in locally-exposed farms was associated (P < 0.05) with increased farm size (in 100 pig increments), shorter distances to the closest PED-positive farm (less than1,001 m), and a disinfectant contact time of less than 20 min. In non-locally exposed farms, PED was associated (P < 0.05) with increased feed truck visits to the farm, no visit of the veterinarian, and again a disinfectant contact time of less than 20 min. These findings suggest that the mechanisms of PED spread in Japan were different for farms closer to case-farms compared to farms that were further away from PED cases. These results will contribute to understanding the epidemiology of the disease in Japan and will ultimately aid in designing and implementing effective prevention and control strategies in Japan and other regions epidemically infected by the PED virus.