Double‐labelling immunohistochemical study of megakaryocytes in African swine fever

Abstract

Bone marrow samples from pigs infected with the highly virulent Malawi'83 or moderately virulent Dominican Republic (DR'78) isolates of African swine fever virus were studied by means of a double labelling immunohistochemical technique which stained the major structural protein VP73 of the virus and megakaryocytes simultaneously. In pigs infected with the highly virulent Malawi'83 isolate, 2.2 per cent of megakaryocytes were VP73+ five days after inoculation, and at six and seven days 2.5 and 9.5 per cent of megakaryocytes were VP73+. Some infected and uninfected megakaryocytes showed pyknosis and karyorrhexis, particularly at seven days after inoculation. However, in comparison with uninfected pigs, the number of megakaryocytes decreased only at seven days after inoculation. In pigs infected with the moderately virulent DR'78 isolate, only 0.2 per cent of megakaryocytes were VP73+ at eight days after inoculation. However, at eight, nine and 10 days after inoculation the total number of megakaryocytes was significantly lower (P < 0.01) than in control uninfected pigs, and the majority of the megakaryocytes showed signs of cell death such as pyknosis and karyorrhexis. The fact that this greater destruction of megakaryocytes was associated with the lower rate of infection of this cell type suggests that indirect damage to megakaryocytes is an additional mechanism of thrombocytopenia in acute and subacute African swine fever.

Understanding and combatting African Swine Fever

“…From 6 dpi onwards, a diffuse or globular cytoplasmic positive reaction is observed both in numerous MPS cells and megakaryocytes (25-30%) (Rodríguez et al, 1996a,b). In other studies, the percentage of immunolabelled megakaryocytes positive for viral antigen after 7 dpi was lower, ranging between less than 1% (Pérez et al, 1997) and 2-10% (Edwards et al, 1985). A positive diffuse or granular cytoplasmic reaction was observed in a small number of granulocytic cells (Rodríguez et al, 1996b).…”

“…In acute forms of ASF, immunoreactivity against viral antigen in bone marrow is detected from 3-4 dpi in monocytes and macrophages that show cytopathic effect. The number of immunolabelled monocytes and macrophages increases after 5 dpi, with presence of occasional immature cells, neutrophils and megakaryocytes (less than 10%) also positive for viral antigen ( peripheral margination of condensed chromatin, pyknosis and karyorrhexis (Pérez et al, 1997). Ultrastructural studies in bone marrow samples taken from animals experimentally infected with highly virulent isolates describe viral replication and cytopathic effect in monocytes, macrophages, reticular cells, immature neutrophils, myelocytes and promonocytes from 3 dpi.…”

“…A higher, but moderate, number of megakaryocytes displayed condensed chromatin, pyknosis or karyorrhexis and a thin rim of cytoplasm. The presence of cell debris and fibrin deposits within the vascular lumen was frequent (Gómez-Villamandos et al, 1997a;Pérez et al, 1997).…”

“…Fibrin and cell debris further appeared within the vascular lumen. By 12 days after inoculation, megakaryocytic hyperplasia along with a substantial number of megakaryocytes undergoing necrosis were observed (Pérez et al, 1997;Rodríguez et al, 1996a,b).…”

Experimental Model of Type II Bovine Viral Diarrhea Virus-Induced Thrombocytopenia in Neonatal Calves

“…13,23,34 In addition to BVDV, several other viruses important in veterinary and human medicine can infect megakaryocytes. 1,3,14,22,28 The megakaryocyte is the hematopoietic precursor cell for platelets. 40 Although megakaryocytes comprise only 0.05% of the nucleated cells in the bone marrow, 16 they are responsible for maintaining the large circulating platelet population.…”