[Comparative physiopathology of Oestrus ovis (Linne 1761) myiasis in man and animals].

Oestrus ovis is an agent of a naso-sinusal myiasis of sheep and goats. This infestation is very frequent and induces clinical signs of rhinitis and sinusitis which are sometimes severe. The pathogenic role of this parasite has been explained until now exclusively because of its size, hooks and spines. Some recent studies indicate the involvement of local hypersensitivity with recruitment of numerous mast cells and eosinophils. Histological nasal mucosal tissue section examination from both sheep and goats showed the presence in considerable numbers of eosinophils and mast cells in lambs receiving single doses of artificial infection were twice as many as the number in control group. In animals subjected to multiple artificial infection the serous mast cell population increased 11-folds and that of mucous mast cells by 5-7 folds when compared with non-infected control groups. Similarly, the eosinophil counts were 17, 29 and 58 times greater in nasal septum, turbinates and sinus in infected groups than their control counter mates. The findings hence suggest that single infection is apparently tolerated by the host while massive cellular recruitment characterizes the cellular responses vis à vis multiple exposure. These reactive cells are localized mainly in the chorion layer just beneath the epithelium with only very few cells in the sub-mucosa level. It is, therefore, presumed that these cells are responsible in limiting parasite (larval) populations and in sustaining the hypersensitivity phenomenon at the site of tissue insult during infection. In naturally infected sheep the mean number of mast cells is only twice that present in parasite free animals. This result is remarkably different from that obtained in repeated artificial infections, probably associated to the difference in cellular response between adult sheep and lambs. It may also possibly explained as resulting from the immunodeficiency induced by parasite antigens. Human beings may be accidently infected. Larvae are deposited by adult flies into conjunctival sacs. Clinical signs of this zoonosis indicate that the pathophysiological processus are different than in animals. Examination of such cases did not confirm the existence of an accompanying allergic reaction in the process.