[Histological tissue study of cattly harboring the Hypoderma lineatum parasite (De Vill.) (Diptera-Oestriform)...

The migrating larvae of H. lineatum throughout the submucosal connective tissue of the oesophagus of cattle induce an acute inflammatory reaction. The aim of this study is to investigate histopathological tissue changes. Connective tissue damage is produced by the inflammatory reaction, but mostly by larval proteolytic enzymes. Fibrous proteins and matrix are all largely affected. Around the larvae there are 3 concentric levels of degradation. The external one is characterized by vascular response. No tissue component is destroyed, but the collagen fibers dissociate into fibrils. In the 2 internal levels (B, C) the fibrils lying along the larvae progressively degrade, splitting into large then small fragments. The elastic fibers are differently affected, but also show breaking and thinness. Finally, the matrix increases, metabhromatic reactions appear, and many mononuclear cells and granulocytes invade this injured area. Fibrin network generally present in inflammatory reaction is not found around the larvae except posteriorly in the regenerative zone. All the changes in the fibrous proteic structures of connective tissue facilitate larval migration. Repair in the larval pathway commences shortly after the passage of the larvae. Necrotic tissues are rapidly destroyed by larval enzymes and tissular and cellular enzymes, macrophages and granulocytes are abundant. The respective importance of larval enzymes and cellular enzymes in the necrotic phase is analyzed. This study, carried out between October and March, also shows an increase of inflammatory reaction and tissular degradation. The immune response of the host and the nutritional habits of the larvae are probably involved.