Study on human ophthalmomyiasis externa caused by Oestrus ovis larva, in Sirte-Libya: parasite features, clinical presentation and management.

Oestrus ovis larva is by far the commonest cause of human ophthalmomyiasis. The larva usually limits it's activity to the conjunctiva and cornea, but, penetration of the eye is a potential complication. Misdiagnosis is common and the condition of acute catarrhal conjunctivitis is ascribed to other causes. The study included 20 patients referred to university hospital of Sirte, Libya. Results showed that the condition was more common among adult male shepherds and farmers in rural areas. Important criteria for diagnosis were; sudden mobile foreign body sensation with abrupt itching and lacrimation occurring in endemic area, in warm months even without history of fly strike. Effective treatment consisted of mechanical removal of the larva by the cotton swap mounting technique which resulted in rapid improvement. Suffocation of residual larvae was mediated by use of liberal amounts of topical antibiotics. Slit lamp examination of larva showed that it was small, translucent, avoid the light beam and easily overlooked. Detailed microscopic examination of larval surface structures revealed a multi-component attachment apparatus consisting of oral hooks, inter-segmental spines, caudal spines and a multi-layered spiny thoracic complex described for the first time. These injurious structures are believed to be responsible through inflicting direct mechanical damage for the observed haemorrhage, ulceration or even the potential invasion, as these changes were more obvious in neglected cases. So, early diagnosis and treatment are essential to avoid complications.