Analysis of African swine fever surveillance data from Poland found the transmission risk between wild boar and domestic pigs to be strongly asymmetric. Wild boar were approximately 50 times more likely to pose a transmission risk to domestic pigs than the reverse. Detections in domestic pigs concentrated in summer, accounting for 84 percent of them, while wild boar detections were more evenly distributed through the year. Only 21.8 percent of domestic pig positive events had a wild boar positive detected in surveillance within 5 kilometres.
That last figure is the one that complicates the picture. If most domestic herd introductions are not accompanied by a nearby detected wild boar case, then either surveillance is missing infected animals in the vicinity or the introduction route is running through something other than immediate proximity. The route reviews in this library describe several candidates: Guinat and colleagues in 2016 place direct contact and contaminated feed as the principal routes, Vasic and colleagues in 2024 document insects and environmental contamination during the Serbian outbreak, and Gebhardt and colleagues detected ASFV across feed manufacturing and production surfaces in Vietnam.
The seasonal concentration has a practical reading for a production site. Summer is when ventilation rates are highest, when openings are most likely to be in use, and when insect activity peaks. A risk profile that rises in one season points toward measures that are seasonal in their attention even where the installed system is permanent, and it argues for treating perimeter, feed and vector control as parts of the same programme rather than as separate ones.