Virus association with lymphocytes in acute African swine fever

This paper reports the presence of mature viral particles within the lymphocytes of samples taken from pigs inoculated with a highly virulent African swine fever (ASF) virus isolate (Malawi 83), and the adhesion of the lymphocytes to macrophages containing the virus replication sites. Virus replication in lymph-node medullar tissue macrophages was observed from 3 days post inoculation (pi). At 3 days pi, transmission electron microscopy revealed hemadsorption in some infected macrophages. At 5 and 7 days pi, a number of macrophages with virus replication were surrounded by a ring of lymphocytes. In such cases, mature viral particles were observed in membrane evaginations of the infected cell that corresponded to invaginations of the lymphocyte membrane. Also at 5 and 7 days pi, mature virions were observed within the cytoplasm of some lymphocytes. However, incomplete virions and African swine fever virus replication sites were not observed within the lymphocytes.