A 58-year-old woman working outdoors on a Greek island sneezed on Oct. 15, 2025, and watched what she described as "worms" come out of her nose. An ear, nose and throat specialist removed 10 fly larvae and one pupa from her maxillary sinus. The pupa is the part that was not supposed to be there.
The case, reported by researchers in Athens and Heraklion in the March 2026 issue of the CDC journal Emerging Infectious Diseases, documents a sheep bot fly reaching the pupal stage inside a human host. The authors state plainly that pupation of Oestrus ovis within any mammalian host is considered biologically implausible. Genetic sequencing matched the specimens to the species with 100% identity against reference sequences in GenBank.
The woman recovered completely after treatment with nasal decongestants. What her case leaves behind is a biological puzzle with two competing explanations, neither of them settled.
Flies Swarmed Her Face in September, and the Coughing Started Weeks Later
The report describes a straightforward exposure. It was September, hot and dry, and the woman was working next to a field where sheep were grazing. She noticed numerous flies swarming around her face.
About a week later, pain began building across her cheeks and midface. Over the following two to three weeks, she developed a severe cough. She reported no other symptoms, and none of her coworkers described anything similar.
Then came the sneeze that sent her to a doctor. The otolaryngologist recovered 10 larvae at various stages of development plus a single pupa from her maxillary sinus, the large air-filled cavity beside the nose.
The research team examined two of the larvae and part of the puparium. One measured roughly 15 millimeters and was yellowish with rows of spines along its underside. The second was light brown, about 20 millimeters long, with broad dark bands across its back. Both were identified as third-stage larvae. The puparium fragment was about 10 millimeters, black and wrinkled, and still held remnants of the pupa. Researchers extracted DNA from the pupal casing and amplified two separate gene fragments, one mitochondrial and one ribosomal, to confirm the identification.
The Life Stage That Should Not Happen Inside a Mammal
In sheep and goats, the fly's natural hosts, the cycle is well mapped. The female deposits first-stage larvae directly into the animal's nostrils. Those larvae crawl upward into the nasal passages and sinuses, feed, grow, and molt. They are eventually expelled as third-stage larvae, burrow into soil, and only then pupate.
Humans are accidental hosts. When Oestrus ovis affects people, it usually deposits larvae in the conjunctival sac of the eye, producing a sudden foreign-body sensation and irritation described in a widely cited review of myiasis in Clinical Microbiology Reviews. Deposits into the nostrils, mouth or ear canal are rare by comparison.
For years, clinicians believed the larvae could not develop past the first stage in a human. That has shifted. Second-stage and third-stage larvae have been recovered from patients more recently, including a nasal case in the Peruvian highlands, typically in people who were immunosuppressed or who had structural abnormalities in the nose. Among five previously reported cases in travelers returning from Greece, four involved first-stage larvae and one involved second-stage.
Pupation is a different matter. Sinuses do not supply the temperature and humidity the stage requires, and host secretions, immune activity, and resident bacteria make the environment hostile. Even in animals, larvae that get trapped in the sinuses are not known to pupate. They dry out, liquefy, or calcify instead.
A Severely Deviated Septum, or Something More Unsettling
The patient had a severely deviated nasal septum, and the researchers believe she was inoculated with an unusually large number of larvae at once.
Their leading hypothesis is mechanical. The combination of a heavy larval burden and a blocked, distorted nasal passage may have prevented the larvae from exiting normally, giving them the time to reach the third stage and, in one case, to pupate in place.
The second possibility is more provocative and, the authors are careful to note, unproven. This case may be an early indication of evolutionary adaptation that would let Oestrus ovis complete its life cycle in humans. The report explicitly calls for more cases and more data before anyone draws that conclusion.
Nothing in the paper establishes which explanation is correct. What the authors do recommend is that clinicians in areas where the fly is endemic keep human bot fly infection in mind.
Where the Actual Risk Sits for Readers
Oestrus ovis is widespread in hot, dry regions, including countries bordering the Mediterranean. A University of Florida profile of the sheep bot fly notes it occurs on all six inhabited continents where sheep are raised, with the highest prevalence in Mediterranean and West African countries. Human cases remain uncommon and are almost always accidental. The infestation does not spread from person to person.
Occupational exposure is the pattern worth noting. Shepherds, farm workers and anyone spending long stretches outdoors near grazing sheep or goats during hot weather face the realistic exposure, and eye involvement remains far more likely than sinus involvement. Reported eye cases include travelers who simply passed through affected regions, as documented in a review of Mediterranean cases published in Parasitology Research.
Symptoms that have brought patients to care include a sudden sensation of something in the eye, redness and tearing, or, in nasal cases, facial pain and irritation. Anyone with those symptoms after outdoor exposure near livestock should be evaluated by a clinician rather than attempting removal at home. One remarkable case does not change medical guidance, and the researchers do not suggest that it should.
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Key Questions Answered
What actually happened to the patient?
She worked outdoors beside a sheep pasture on a Greek island in September and noticed flies around her face. Facial pain and a severe cough followed. In mid-October she sneezed out larvae, and a specialist removed 10 larvae and one pupa from her sinus.
Why do researchers call pupation biologically implausible?
Sheep bot fly larvae normally leave the host before pupating, and a human sinus does not provide the temperature, humidity or microbial conditions the pupal stage needs. Even in sheep and goats, trapped larvae dry out rather than pupate.
How was the parasite identified?
Researchers examined the specimens under magnification, then extracted DNA from the pupal casing and sequenced two gene fragments. Both matched published Oestrus ovis sequences exactly.
Does this mean the fly is now infecting humans more easily?
No one knows. The authors offer two explanations, a mechanical one involving her severely deviated septum and a large larval dose, and a speculative one about early parasite adaptation. They state that more cases are needed to distinguish between them.
Who is most at risk?
People with sustained outdoor exposure near grazing sheep or goats in hot, dry regions. Most human cases involve the eye rather than the sinuses, and the condition does not pass between people.
Did the patient recover?
Yes. After surgical removal of the larvae and pupa and treatment with nasal decongestants, she made a complete recovery.
