Microscopic examination revealed the objects to be fly larvae. They were whitish, transparent, oval shaped with a length of 1 mm by 0.33 mm of width (see Fig. 1A in the case presentation [1]), with 12 rows of cuticular spines on both sides (2, 3). The cephalic segment was distinguished with two mandibles curved in a semicircle and two longitudinal appendages (see Fig. 1B in the case presentation [1]). The caudal segment consisted of two tubercles, each containing about 10 curved spines (see Fig. 1C in the case presentation [1]). These morphological characteristics were suggestive of first-instar larvae of Oestrus ovis.
O. ovis is a fly species that deposits larvae in the nostrils of sheep and goats while remaining in flight (4, 5). Larvae migrate into the nasal cavities and sinuses in order to develop. They mature in about 8 months before being eliminated by sneezing. By accident, when they cannot find their usual hosts, O. ovis can deposit larvae on other species, but the larvae cannot develop to maturity in humans, who are dead-end incidental hosts.
Edmond and Etienne Sergent of Pasteur Institute of Algeria published the first description of a human ophthalmomyiasis caused by O. ovis in 1907 under the name of “thim’ni,” which meant “sheep fly” in a Berber dialect (6).
This infestation is characterized by sudden intense ocular pain with foreign body sensation due to strong attachment of larvae to the conjunctival mucosa by powerful mandibles. Progression to conjunctivitis and rhinorrhea is possible, sometimes complicated by keratitis or even intraocular infection. In our case, after removal of the larvae, an antibiotic collyrium was prescribed, and ophthalmology consultations at day 2 and 7 revealed no complication.
Risk factors were investigated and revealed an animal fair near the patient’s home 4 days earlier that could explain the presence of O. ovis. More than 110 years after the first description by the Sergent brothers, this case raises once more the initial hypothesis, which suggested that the frequency of this accidental infestation in man is of greater potential where sheep are rare and the population is dense.
Contributor Information
Julien Lesaca, Email: julien.lesaca@gmail.com.
Erik Munson, Marquette University.
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