Early‐phase risk assessments during the first epidemic year of African swine fever outbreaks in Vietnamese pigs

Abstract

Background African swine fever (ASF) is a notifiable viral disease of pigs and wild boars that could lead to serious economic losses for the swine industry. Objectives The aim of this study was to identify risk factors in the early phase of ASF outbreaks in Vietnamese swine herds during the first epidemic year. Methods The period of interest for this case–control study was February to July 2019. A questionnaire was administered in northern Vietnam where all early cases of ASF were reported. Producers of herds with reported cases were asked to provide information starting from the day of onset of clinical signs as well as 30 days prior to that day. The period of interest for controls was within the 6 months of the first outbreak in Vietnam (February 2019). Questionnaires included 55 questions; responses were received from 67 cases and 115 controls. Logistic regression analysis was used to identify factors associated with ASF status. Results Thirty‐seven variables of interest (among a total of 55 variables) were associated with ASF status in univariate analysis (p < 0.05). These 37 variables were assessed for inclusion in the multivariate analysis by backward stepwise selection. Six variables remained significant as ASF risk factors in the final model: distance to farm within 500 m, distance of irrigation systems within 200 m, total number of pigs (≤500), absence of dressing rooms for workers/visitors before entering the farm, poor hygienic practices for people within the farm, and poor hygienic practices at pig loading/unloading locations. Conclusions These results may help in understanding the epidemiology of ASF in Vietnam and provide a scientific basis for optimization of current interventions and development of new tools and strategies to reduce transmission of ASF.

Estimation of the herd-level basic reproduction number for African swine fever in Vietnam, 2019

“…Pig population density is one of the critical risk factors that may have also influenced R 0 values [ 13 ]. The higher density of pig farms would increase the number of contacts between farms through the movements of pigs, persons, vehicles, or equipment [ 24 ].…”

What can we learn from the five-year African swine fever epidemic in Asia?

“…As in China, the small farm sector is declining but may take time to be fully replaced by modern commercial farms ( 97 ). In these areas, people often cannot properly dispose of infected animals and dump the carcasses in rivers or roadside shrubs after slaughter, causing the disease to spread even further ( 102 , 122 , 129 , 130 ). This can be partially explained by the limited capacity of veterinary services to deal with epidemics at the municipal level.…”