Experimental comparison of African swine fever virus exposure through contaminated feed and infected pig organ homogenate

Introduction – African swine fever virus (ASFV) causes a devastating hemorrhagic disease in swine. Oral exposure through ASFV-contaminated feed or ASFV-infected pork products represents a major transmission pathway; however, the relative risk associated with these two exposure scenarios remains incompletely defined under controlled experimental conditions. Methods – In this study, we conducted three independent in vivo experiments in domestic pigs to compare oral ingestion of genotype II ASFV isolated from Vietnam via contaminated commercial feed (dry and wet forms; 2 × 10⁶ HAD₅₀ per pig) and ASFV-infected organ homogenate prepared from spleen and liver (5 × 10⁶ HAD₅₀ per pig). Clinical signs were monitored daily for 28 days, and virological testing and gross lesions were assessed according to the predefined sampling and necropsy schedule. Results & Discussion – None of the feed-exposed pigs (dry feed, n = 5; wet feed, n = 3) showed clinical signs, viremia, or gross lesions during the experimental period. In contrast, oral administration of ASFV-infected organ homogenate (n = 5) resulted in 100% mortality (mean survival: 8.4 ± 1.8 days). Viremia was first detected at 2.8 ± 0.5 days post-infection (dpi), followed by sequential onset of oral (3.2 dpi), nasal (4.0 dpi), and rectal (4.4 dpi) shedding. All organ homogenate-fed pigs exhibited gross lesions consistent with acute ASFV infection, including hemorrhages in the spleen, kidneys, liver/gallbladder, and multiple lymph nodes. Under the conditions tested, exposure to commercial feed experimentally spiked with ASFV did not result in detectable systemic infection, whereas ingestion of infected organ homogenate consistently produced acute ASF. These overall results emphasized the critical importance of both feed safety protocols and continued enforcement of swill-feeding bans and safe disposal of infected carcasses.