Infection of the Conceptus With African Swine Fever Virus Following Artificial Insemination in Sows: A Pathological Study.

African swine fever virus (ASFV) has recently been shown to be transmissible via artificial insemination (AI) with contaminated semen. In this study, we performed a comprehensive pathological investigation to assess vertical transmission and infection of the conceptus. A total of 14 gilts were experimentally inseminated and examined by clinical monitoring, virological analyses, gross and histopathology, immunohistochemistry, and combined RNAScope in situ hybridization and immunofluorescence to localize viral antigen and nucleic acids and to characterize infected cell populations. ASFV infection of conceptuses was demonstrated, supporting the possibility of vertical transmission. Viral antigen and nucleic acids were widely distributed across multiple tissues of the conceptus, indicating systemic infection. Infection patterns showed considerable heterogeneity, with variable viral load, morphology, and antigen detection observed both between animals and among conceptuses from the same uterus. Gross examination revealed uterine alterations, including hyperemia, edema, and accumulation of intrauterine fluid, frequently associated with embryonic loss or remnants of extraembryonic membranes. In the female reproductive tract, viral antigen was detected in multiple compartments, including the ovary, uterus, cervix, and vagina. Notably, viral antigen was detected in either maternal or fetal compartments but not simultaneously, indicating a temporally dynamic and spatially distinct pattern of infection and suggesting that multiple routes of maternal-to-conceptus transmission may be involved. Colocalization studies in fetal tissues revealed that ASFV-infected cells included subsets expressing macrophage-associated markers such as CD163 and Iba-1, while a substantial proportion of infected cells could not be phenotypically assigned, indicating a broader and incompletely defined cellular tropism. Together, these findings provide new insights into ASFV transmission biology and pathogenesis in early gestation and highlight the complexity of maternal-to-conceptus transmission, warranting further investigation of infection dynamics at the feto-maternal interface and the identity of fetal target cell populations.