The Role of Wildlife and Pests in the Transmission of Pathogenic Agents to Domestic Pigs: A Systematic Review

SIMPLE SUMMARY: The processes of globalization, human activities, and the growing popularity of outdoor ecological pork production contribute to increased interactions between domestic pigs and wildlife. Wild animals and pests can carry harmful pathogens that pose a threat to domestic pigs, resulting in economic losses at the local, national, and global levels. However, our understanding of the specific pathways through which these pathogens are transmitted between these animals is limited. This review has collected and examined information on the diversity and extent of pathogen spread from various wild animals and pests to domestic pigs. In the European context, our assessment showed that wild boars accounted for 80% of the documented pathogen transmission, followed by rodents (7%) and deer (6%). Insects, wild carnivores, wild birds, cats, and badgers had a lower representation in the studies. Farms with low biosecurity levels, particularly in extensive rearing systems, were identified as higher-risk farms. In general, 65.5% of the included studies supported possible risks and risk factors with quantitative data. Based on these findings, it is recommended to implement proper farm biosecurity measures, strong fences, and control programs for rodents, pets, and insects, particularly in high-risk areas. It is also crucial to monitor wildlife and raise awareness among farmers about the risks associated with disease transmission. ABSTRACT: Wild animals and pests are important reservoirs and vectors of pathogenic agents that can affect domestic pigs. Rapid globalization, anthropogenic factors, and increasing trends toward outdoor pig production facilitate the contact between domestic pigs and wildlife. However, knowledge on the transmission pathways between domestic pigs and the aforementioned target groups is limited. The present systematic review aims to collect and analyze information on the roles of different wild animal species and pests in the spread of pathogens to domesticated pigs. Overall, 1250 peer-reviewed manuscripts published in English between 2010 and 2022 were screened through the PRISMA framework using PubMed, Scopus, and Web of Science databases. A total of 84 studies reporting possible transmission routes of different pathogenic agents were included. A majority of the studies (80%) focused on the role of wild boars in the transmission of pathogenic agents to pig farms. Studies involving the role of rodents (7%), and deer (6%) were the next most frequent, whereas the role of insects (5%), wild carnivores (5%), wild birds (4%), cats (2%), and badgers (1%) were less available. Only 3.5% of studies presented evidence-based transmission routes from wildlife to domestic pigs. Approximately 65.5% of the included studies described possible risks/risk factors for pathogens’ transmission based on quantitative data, whereas 31% of the articles only presented a hypothesis or qualitative analysis of possible transmission routes or risk factors and/or contact rates. Risk factors identified include outdoor farms or extensive systems and farms with a low level of biosecurity as well as wildlife behavior; environmental conditions; human activities and movements; fomites, feed (swill feeding), water, carcasses, and bedding materials. We recommend the strengthening of farm biosecurity frameworks with special attention to wildlife-associated parameters, especially in extensive rearing systems and high-risk zones as it was repeatedly found to be an important measure to prevent pathogen transmission to domestic pigs. In addition, there is a need to focus on effective risk-based wildlife surveillance mechanisms and to raise awareness among farmers about existing wildlife-associated risk factors for disease transmission.