A Histological Study Of The Larval Salivary Glands Of The Sheep Nasal Bot Fly Oestrus Ovis Linnaeus (Oestridae - Diptera) With Observations On The Larval Distribution

Abstract

The larvae of Oestrus ovis are well known parasites inhabiting the nasal passages and adjoining cavities in sheep. Besides causing myiasis of the nasal cavities of sheep, these larvae are also known to attack man occasionally causing an ocular myiasis (Opthalmomyiasis). These larvae have gained an almost cosmopolitan distribution and have attracted attention in practically every country of the world from earliest times. However, there is no published work on this pest in Kenya. Thus, the first part of the present study involves an investigation of the number of larvae found in a sheep head, their exact location, and the damage they do For the purposes of this study, regular visits were made to slaughter houses in and around Nairobi and the heads of freshly slaughtered sheep obtained. Each head was divided transversely with a powerful saw to open the frontal sinuses. The anterior part was further divided by sagittal cuts on either side of the nasal septum so that the mucosa of the septum and the turbinal bones could be easily and thoroughly examined. 2 It was observed that the 1st instar larva are found in the lower nasal passages. They may be found in the upturned nostrils of the sheep, on the muzzle near the nostrils, in the folds of the turbinal bones or between the later bones and those of the skull. The 2nd and 3rd instar larvae are found in the upper nasal passages and in and around the frontal and maxillary sinuses. A maximum of 14 larvae (2nd and 3rd ins tars) of which 4 were dead, were recorded from the frontal sinuses of a single sheep. Only on one occasion were larvae found in the pharyngeal region. The larvae have two dark, sharp and curved mouth hooks and many row of sharp spins on their ventral surface. They use this armature for moving about, attaching themselves and feeding on the mucous membranes that line the head cavities. As a result of this activity, inflamation, which becomes mucoid purulent is always observed in a dissection of any infested head..........