Lymphadenopathy and expression of nodal mast cells and eosinophils in the myiasis by human bot fly

Wistar rats (Rattus norvegicus) infested with Dermatobia hominis (L. Jr., 1781) had their axillary lymph nodes removed and histopathologically processed. Follicular hyperplasia in the germinal center was noted from 2 d postinfestation (dpi), exhibiting a high number of centerblasts, mitotic and apoptotic cells, and a thin parafollicular area. The paracortex showed hyperplasia rich in dendritic cells, immunoblasts, and endothelial venules, with diapedesis seen from 4 dpi onward. Hyperplasia of the medullar sinus also was first observed at this point, as well as dilated lymphatic sinus, lymph, macrophages, neutrophils, mast cells, and eosinophils. Medullar strings were expanded and filled with immunoblasts, mitotic cells, and plasmocytes. Lymphadenitis was not observed. The expression of mast cells was similar for both myiasis-affected and control rats but increased significantly (mastocytosis) at 7 and 15 d postlarval emergence (dple). Eosinophilia was observed at 4, 10, 15, 20, and 28 dpi as well as at 2, 7, and 15 dple, particularly on the last three observations of dpi and the earliest dple. This experimental approach allowed progressive tissue reactions in the lymph nodes to be monitored during myiasis, particularly those involving mast cells and eosinophils. These reactions abated and complete repair was observed at 60 dple.