Experimental skin lesions from larvae of the bot fly Dermatobia hominis.

Skin biopsies from larvae of Rattus norvegicus, experimentally infested with Dermatobia hominis (Linnaeus Jr) (Diptera: Cuterebridae), were processed for histopathological studies. Two days after infestation, the first-stage larvae (L1) were located deep in the dermis, surrounded by an inflamed area infiltrated predominantly by neutrophils. On the fourth day a thin necrotic layer could be seen close to the larvae, surrounded by large numbers of neutrophils, lymphocytes, macrophages with a few eosinophils and mast cells. A small warble was formed after the fourth day, increasing in size until the seventh day, when the L1 moulted to the second-stage larva (L2). The inflammatory process continued with increasing numbers of neutrophils, macrophages, lymphocytes, eosinophils and mast cells invading the area, as well as the proliferation of fibroblasts and endothelial cells and the appearance of a few localized haemorrhages. After 18-20 days, the L2 moulted to the third-stage larva (L3), when a few plasma cells could be seen in the inflamed area. At 25-30 days there was a reduction in the necrotic layer, as well as in the number of neutrophils and lymphocytes, although large amounts of eosinophils, plasma cells, and collagen fibres were seen. The L3 usually left the host after 30 days. Two days later, the larval cavity was reduced, mast cells infiltrated the region and collagen fibre production were increased. After 7 days, an intense infiltration of plasma cells and scattered necrotic areas could be seen. A scar formed after 10 days. This study showed the laboratory rat to be a suitable model for studies of D. hominis infestation.