Mechanical transmission of African swine fever virus (ASFV) has been investigated on few occasions, with Stomoxys calcitrans experimentally shown to transmit ASFV which was detected in various body parts for 3 days after infection. However, up to date, there is no field evidence demonstrating the presence of viral DNA in blood-feeding arthropods. For this purpose, 30 pig farms from Romania where ASF was confirmed were selected for sampling according to a risk scoring system. In 9 farms, pigs were still present at the time of sampling, whereas on the other outbreak farms pigs were culled maximum 24h before. Trapping of vectors was done using standard entomological methods and mainly Culicoides spp. and S. calcitrans were collected. After the morphological identification of insects, they were pooled and tested for the presence of ASFV DNA using PCR tests. A total of 200 pools (119 from 20 farms with Culicoides and 81 from 15 farms with S. calcitrans) were prepared. 50.5% of the pools were positive for ASFV DNA. The prevalence of infected pools was the highest in commercial farms. The proportion of ASFV DNA positive pools in S. calcitrans (62.96%) was significantly higher than in Culicoides spp. (42.02%). Positive pools were found in 55% of the locations for Culicoides spp. and in 86.7% for S. calcitrans. The prevalence was significantly higher in farms were sampling was done when pigs were still present compared to farms where the pigs were already culled. This study demonstrates that the most common vectors found around pig farms are Culicoides spp. and Stomoxys and the ASFV DNA can be detected in both groups with higher probability in commercial farms and if tested when pigs are present at the time of sampling. Despite the positive findings of ASFV DNA, the actual role in ASFV mechanical transmission remains to be clarified.

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