Parasite retention and entanglement at the dermal infection initiation site.

Scanning electron microscopy images of 90 hpi dermal ear sections illustrating presence of parasites in the connective tissue close to the cartilage layer of the ear. Subcutaneous adipocytes were readily identified by the smooth external appearance of their cytoplasmic membrane and the characteristic presence of a surrounding collagen network known as basket [34]. Parasites are indicated with white arrows (A). Intricate interactions of trypanosomes with adipocytes in the connective tissue were observed frequently (B-G). Parasites were found with the anterior part buried inside the adipocyte (D-G). Parasites were prominently entangled by reticular fibers (white arrows) of the periadipocytic baskets (E- H) and are embedded in collagen bundles (J-M). Despite these interactions, trypanosomes were proliferating as many cells had multiple flagella (H-J). These observations were made in two independent scanning electron microscopy experiments with a total of eight parasite infected ears at 90 hpi. Sc, stratum corneum; Ep, epidermis; Ad, adipocyte; Ct, connective tissue; Ca, cartilage; Rf, reticular fibers; p, posterior trypanosome end; Cb, collagen bundle.