OBSERVATIONS ON THE HISTOPATHOLOGICAL CHANGES CAUSED BY THE LARVAE OF HYPODERMA BOVIS (L.) AND HYPODERMA LINEATUM (DE VILL.) (DIPTERA: OESTRIDAE) IN TISSUES OF CATTLE

Abstract

The lesions in submucosal and adventitial connective tissue of the oesophagus of cattle caused by the migrating larvae of Hypoderma lineatum (De Vill.), consist of pseudocystic areas and tracks of a gelatinous fibrinous exudate containing necrotic cellular debris and collagen fibres in various stages of dissolution surrounded by accumulations of eosinophils and lymphocytes. The larvae feed on the dissolved connective tissue. These changes suggest that migration through the tissues is mainly by enzymic dissolution of collagen fibres and ground substance. Similar changes were found in the connective tissue surrounding the muscles of "licked beef". The larvae of H. bovis (L.) in the epidural fat cause areas of fat necrosis and sometimes invade the periosteum and dura. The greenish colour of the tracks is due to infiltrations of eosinophils. The warble shows a mixed picture of chronic granulomatous and non-suppurative inflammation, encapsulated by dense fibrous tissue. The larva is surrounded by a vascular layer of granulation tissue infiltrated with eosinophils, large mononuclears and plasma cells. Numerous giant cell systems and pseudotubercles are present. The larvae feed on the exudate within the warble cavity. Areas of suppuration are rarely found. The healing of the warble and the reaction to dead larvae are described.