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Table 2 Summary of histopathological findings in selected tissues of sheep infected with BTV-2 (RSA1973/03)

From: Involvement of the skin during bluetongue virus infection and replication in the ruminant host

Animal Skin non-midge fed** Skin midge fed*** Tonsil Lips Lung
Sheep VH56/ 3 dpi Minor engorgement, with indistinct vacuolation of epidermal cells. Mildly oedematous/focal epidermal crusts/mild dermal inflammation *(lymphocytes, plasma cells and eosinophils). Epithelial cells markedly vacuolated. Low numbers of eosinophils in tonsil itself. Oedematous (especially around capillaries) and inflamed* (lymphocytes, plasma cells and eosinophils). Indistinct vacuolation of lip epidermal cells. Peribronchial connective tissue is markedly oedematous and moderately inflamed*(lymphocytes, plasma cells and eosinophils).
Sheep VH67/ 4 dpi Moderate oedema around capillaries and mild engorgement, mild aggregation of plasma cells around capillaries. Moderately oedematous, especially around capillaries, with mild engorgement. Mild aggregation of plasma cells around capillaries, low numbers of neutrophils and eosinophils. Focal collagen necrosis.
Note: C. sonorensis were last fed on this sheep 48 h prior to collection of skin samples.
Epithelial cells markedly vacuolated. Moderate numbers of eosinophils in connective tissue just below epithelium. Focally dense aggregates of lymphocytes and plasma cells especially around capillaries and adnexae in mid dermis, lighter inflammation in superficial dermis. Moderate inflammation *(lymphocytes, plasma cells) of peribronchial connective tissue.
Sheep VH58/ 6 dpi Mild oedema and moderate engorgement, sparse dermal inflammation *(neutrophils, lymphocytes, plasma cells) Moderately oedematous and engorged, with focal degeneration of epidermis. Moderate to marked diffuse dermal inflammation (Figure 2a) *(lymphocytes, plasma cells, eosinophils), with scattered foci of, predominantly, eosinophils associated with collagen necrosis. Epithelial cells vacuolated. Glassy appearance to nuclei of macrophages, lymphocytes, plasma cells in lymphoid parenchyma. Oedematous (especially around capillaries) and inflamed *(lymphocytes, plasma cells, eosinophils) – focally markedly so. Indistinct vacuolation of epidermal cells, but also apoptosis, epidermal oedema and erosion. Peribronchial connective tissue is moderately oedematous and moderately inflamed *(plasma cells, lymphocytes).
Sheep VH57/ 8 dpi Moderate oedema with mild perivascular inflammation *(lymphocytes and plasma cells). Markedly oedematous (dermis and epidermis). Moderate to marked diffuse dermal inflammation around capillaries *(plasma cells, lymphocytes, eosinophils, neutrophils). Some crusts of surface and dermal foci of macrophages, plasma cells, lymphocytes and eosinophils, including granulomas in superficial dermis (neutrophils and eosinophils centrally with encircling epithelioid macrophages (Figure 2b). Epithelial cells moderately to markedly vacuolated, numerous lymphocytes and plasma cells in epidermis. Glassy appearance to nuclei of macrophages, lymphocytes and plasma cells in lymphoid parenchyma. Moderately oedematous (especially around capillaries) and moderately inflamed *(plasma cells, lymphocytes, rarely eosinophils). Peribronchial connective tissue moderately oedematous and moderately inflamed *(plasma cells, lymphocytes). Diffuse engorgement and congestion.
Sheep VH66/ 9 dpi Minor vacuolation of deep sweat gland cells as well as mild oedema with mild perivascular inflammation *(lymphocytes and plasma cells). Moderate perivascular oedema and engorgement with patchy haemorrhage. One capillary contained a fibrin thrombus. Moderate to marked inflammation (plasma cells, lymphocytes, eosinophils, and neutrophils). Areas of markedly vacuolated epithelial cells. There are also areas containing large numbers of lymphocytes and plasma cells in the tonsillar epithelium. Engorged, haemorrhagic and oedematous (especially around capillaries) with mild inflammation *(plasma cells, lymphocytes, eosinophils and macrophages). Endothelial cells in the walls of some capillaries are degenerate. Modest peribronchial inflammation *(plasma cells lymphocytes). Mild oedema, moderate engorgement, small numbers of vessels contain fibrin thrombi.
  1. * The order in which the leukocyte subsets are described correlates to their relative abundance.
  2. ** Skin collected from the site of the inner thigh not fed upon by Culicoides.
  3. *** Skin collected from the site of the inner thigh immediately after it was fed upon by C. sonorensis.