Abstract
Unilateral nasal symptoms in patients with lowered immunity who have recently been to North Africa may be due to infestation with the nasal bot fly.
The enclosed picture shows the posterior face of a puparium of Oestrus ovis (approximately 1.6 cm in length), developed from a third instar (final developmental stage) larva, which was sneezed from the nose of a 68-year-old Devon man on steroids and azathioprine, who had developed itching in the left nostril 3 months earlier during a beach holiday in Tunisia.
Oestrus ovis is a nasal bot fly, more commonly causing myiasis (fly larva infestation) in sheep and goats worldwide. 1 This is one of the three reliable documented cases of a larva of this species reaching the third instar stage in a human.2,3 It appears to be the most mature larva found, evidenced by its continued development to a puparium. Two of the three patients (like the patient described) were immunocompromised, the one with HIV 2 and the second (our patient) with medication, but the third appeared otherwise healthy. 3
The gravid female fly ejects larvae directly into the nose of the unsuspecting host, where they colonise the nasal cavity and develop, feeding via extracorporeal proteases acting within the nasal passages. 4 When fully matured the larvae leave the host, for puparation, waiting for adult emergence dependent on environmental factors, when they then go on to start the next generation.
During the 3 months following the Tunisian holiday, the patient had symptoms of hay fever, which he treated himself with partial success using antihistamines. The symptoms of unilateral left nasal blockage persisted, however, until he sneezed out a larva (which developed into the pupa pictured) on the day of his attendance at his general practitioner surgery. Fortunately, the patient was well following this with a patent normal left nasal passage and no further treatment was required.