THROMBOCYTOPENIA ASSOCIATED WITH APOPTOTIC MEGAKARYOCYTES IN A VIRAL HEMORRHAGIC SYNDROME INDUCED BY A MODERATELY VIRULENT-STRAIN OF AFRICAN SWINE FEVER VIRUS

A viral haemorrhagic syndrome was induced in 14 pigs by inoculation wi th an African swine fever (ASF) virus strain of moderate virulence, to determine changes in megakaryocyte (MK) numbers and morphology and th us to assess the role of these cells in the thrombocytopenia character istic of subacute ASF. The strain tested induced changes in the propor tion of different types of MK (typical nucleated MKs, apoptotic MKs an d immature MKs); it also caused subcellular lesions over the first 7 d ays post-inoculation (dpi). At 7 dpi, severe thrombocytopenia was obse rved. There was a statistically significant increase in apoptotic MK n umbers. The MKs showed three stages in the course of the disease: a co mpensatory stage, represented by cytoplasmic projections, a hypermatur ity stage, represented by apoptotic MKs, and a regenerative stage, rep resented by clusters of immature MKs. These changes, especially the pr esence of numerous apoptotic MKs, may explain the early and transitory thrombocytopenia detected in subacute ASF. The large number of apopto tic MKs observed may be associated with the accelerated maturation of these cells, resulting from the action of cytokines, or peripheral pla telet consumption, or both. (C) 1998 W.B. Saunders Company Limited.