African Swine Fever Outbreaks in Lithuanian Domestic Pigs in 2019

SIMPLE SUMMARY: In Lithuania, African swine fever (ASF) notifications in domestic pigs and wild boar have been increasing since the entry of ASF from 2014 to 2018. The disease caused serious economic losses and affected commercial and non-commercial pig holdings. We conducted a prospective matched case-control study to investigate the potential risk factors associated with ASF outbreaks in pig farms in Lithuania in 2019. The study revealed that the risk of ASF occurrence in a pig farm was significantly lower if the farm had been inspected by veterinary inspectors, while the risk increased if certain activities, possibly related to the indirect transmission of ASF to a pig farm, were practiced on a farm, e.g., mushroom picking, sharing equipment, etc. Veterinary inspection seemed to increase the level of biosecurity and ASF awareness on a farm, which may have helped to prevent disease introduction. These findings can be used to improve the control and prevention of ASF in domestic pigs in countries affected by ASF. ABSTRACT: While numerous risk factors of African swine fever (ASF) transmission to domestic pigs have been described, ASF virus introduction has often not been traced back to one single defined cause. The large number of ASF outbreaks that occurred in domestic pigs in Lithuania from 2014 through to 2018 raised the question regarding whether outbreak-specific risk factors and transmission routes could be identified. Therefore, a prospective matched case-control study was designed. Data from 18 outbreaks that occurred in Lithuanian in 2019 and 36 control farms were analyzed. Conditional multivariable logistic regression showed that two or more visits by veterinary inspection of a farm had a significant preventive effect on the occurrence of ASF on a farm (Odds ratio (OR) 14.21, confidence interval (CI) 1.09–185.60 for farms not inspected vs. farms inspected twice or more a year), while certain practices (e.g., mushroom picking, sharing equipment, etc.), which might facilitate the indirect introduction of ASF from fields and forests into piggeries, significantly increased the odds of an outbreak (OR 5.18, CI 1.10–24.44). The results of the study highlight the importance of veterinary inspections for increasing the biosecurity level on pig farms and the awareness of ASF. The knowledge on potential protective and risk factors may help to improve the prevention and control of ASF outbreaks in domestic pig farms in Lithuania and other affected countries.