Cutaneous myiasis. Immunohistologic and ultrastructural morphometric features of a human botfly lesion

This study documents the immunohistologic and ultrastructural morphometric features of a case of cutaneous myiasis due to Dermatobia hominis. The mixed host inflammatory response surrounding the larvae included lymphoblasts, eosinophils, activated fibroblasts, mature histiocytes, mast cells, plasma cells, and Langerhans cells, indicating a complex interactive immunologic response to the botfly parasite. Immunotyping revealed that the dominant dermal cells were activated (Ia⁺) T-helper cells. Although the strikingly elevated T-helper/T-suppressor cell ratio might suggest a monoclonal infiltrate, a mixture of Leu 8⁺ and Leu8^- T-cells indicates both immunoregulatory subsets of T-helper cells as found in a reactive process. Furthermore, our ultrastructural histogram found the lymphoid nuclear shapes were oval with few nuclear invaginations as found in inflammatory infiltrates. As indicated by electron microscopy, there were abundant activated fibroblasts elaborating collagen which may relate to larval containment.