African swine fever in wild boar: carcasses, density and movement remain the key transmission drivers

A new systematic review of 54 modelling studies reaches a complementary conclusion: African swine fever persistence in wild boar cannot be explained by a single factor. Across Europe and Asia, infected carcasses, wild boar density and movement emerge most consistently, while habitat and seasonality shape local transmission.

A recent EFSA-supported analysis has already refined the role of wild boar density, showing that density appears more important for the geographical expansion of ASF than for persistence once the virus is established; local environmental and epidemiological conditions then become more influential.

Published in iScience, the review covers studies from 29 countries published between 2014 and 2024. Risk-factor and spatiotemporal models dominated the literature, while comparatively fewer studies quantified transmission dynamics or intervention effectiveness.

Carcasses remain central

The wild boar–environment cycle appeared in 38 of 54 studies, or 70.4%. Infection was maintained through direct contact and indirect exposure to contaminated carcasses, soil and water. Cold conditions and forest environments were repeatedly associated with longer environmental persistence.

This explains why ASF can persist even after wild boar numbers decline. The review therefore identifies carcass detection and removal, passive surveillance and environmental management as major control priorities.

Density matters, but movement connects populations

Wild boar density was one of the most frequently reported risk factors, alongside movement and infected carcasses. Movement and habitat connectivity allow the virus to spread between subpopulations, while forest cover, habitat suitability and proximity to previous outbreaks can modify risk locally. main

ASF detections also tended to peak during the colder months, particularly from November to April.

The domestic pig interface remains important

Twelve studies, 22.2%, examined transmission between wild boar and domestic pigs. This pathway was particularly relevant where wild-boar habitat overlapped with lower-biosecurity pig production. Potential bridges included contaminated feed, water, hunting equipment, fomites and human activity.

Models still have major limitations

Only seven studies reported estimates of R0, with values ranging from about 1.14 in Sardinia to above 4 in some South Korean seasonal models. Because methods differed considerably, the authors warn against direct comparison. Validation and uncertainty assessment were also inconsistent. In studies modelling interventions, 70% had unclear or high risk regarding uncertainty analysis.

The practical conclusion is therefore not that one model or one factor explains ASF. Carcass management, surveillance, wild boar movement and density, and strong farm biosecurity must be combined and adapted to local ecological conditions.