Potential for Introduction of African Swine Fever Virus into High-Biosecurity Pig Farms by Flying Hematophagous Insects

Background. DNA of African swine fever virus (ASFV) has previously been detected in hematophagous insects on ASF outbreak farms. However, it remains unclear whether the viral DNA derived from blood meals that originated from pigs on the outbreak farm or was introduced from infected domestic pigs or wild boar sources located outside of the outbreak farm. Methods. We caught 644 hematophagous insects on the windows at two non-outbreak high-biosecurity pig farms (i.e., without ASFV-infected pigs) using plastic meshes coated with sticky glue, as well as 3576 hematophagous insects using H-traps on or around the farms. Using PCR analyses, we identified which insects were present, whether these hematophagous insects carried blood from an external (exogenous) source and if the blood contained ASFV DNA. Results. We found blood meals with ASFV DNA in one pool of five Haematopota spp. in the H-traps. From the window traps, we found 0-2.7% of Haematopota spp., Stomoxys calcitrans, and Aedes spp. carrying blood meals from exogenous sources into the farms. Some insects carried bovine blood; the closest registered source for this was 2500m from the pig farm. Conclusion. Hematophagous insects carrying ASFV-positive blood meals or blood meals from exogenous sources seem to be attracted to high-biosecurity pig farms and attempt to enter them through their windows. Despite the small percentage of insects carrying blood and the small amounts carried by each insect, the large numbers of insects result in a sufficient volume of exogenous blood, potentially containing ASFV, to constitute a non-negligible risk for ASFV-introduction into unprotected pig stables. This study is the first to provide quantitative data on the number of hematophagous insects trying to enter high-biosecurity pig farms. It is also the first to provide information about the origin of their blood meals, indicating that insect-borne introduction of blood containing ASFV into high-biosecurity pig farms is possible and, therefore, could potentially be responsible for some of the outbreaks observed during the summer peaks of infection.