Rare infestation of Oestrus ovis in gardener’s eye
In a rare case, a team of doctors from the University Hospital of Saint-Etienne in France recently reported the case of a gardener whose itchy eye was caused because of an infestation of maggot larvae of Oestrus ovis in the eye. The 53-year-old patient presented to the emergency department with the complaint of an itchy right eye. It was later diagnosed to be caused because of the presence of maggot larvae in the cornea. The paper highlighting the diagnosis and treatment of Oestrus ovis infestation was published in the New England Journal of Medicine.
Sheep bot flies or Oestrus ovis are a common occurrence in France, and they are named after their tendency to lay eggs in the nostrils of sheep. Once the eggs are deposited, the larvae then travel their way up to the nostrils and inhabit there. They feed on the mucus and develop into maggots. A few weeks after the inhabitation, the maggots drop out of the nose and finish their maturation process, growing into adult fleas. According to recent studies published on maggot larvae infestation of the eyeballs have shown that in some cases, the female flies may get confused and lay their eggs on the eyeballs instead. The presentation is otherwise rare in humans.
In this case, the patient presented to the emergency after he felt like something had entered his eye. He further told the doctors that he experienced it when he was working in his garden close to sheep and a horse farm. In addition, he felt as though something had run into his eye. Several hours later when the problem did not subside on its own, he decided to visit the emergency department for help. This was when he first presented to the emergency department of the hospital.
After examining the patient, the doctors initially diagnosed the 53-year-old with ophthlamomyiasis, an infestation of the eye with fly larvae. Further examination revealed that the presence of the larvae had also caused conjunctival hyperemia. Conjunctival hyperemia is defined as a dilation of the blood vessels. However, there were no other signs of abrasion noted because of the body spicules of the larvae. The study further highlights that there were over a dozen mobile larvae in the patient’s eye.
Treatment included removing the larvae one by one with the help of tiny tweezers. Doctors further prescribed the patient a round of antibiotics to prevent infection. Ten days after the procedure, the patient returned for a follow-up with no signs of eye damage or infections. The larvae were also filmed and photographed and described as follows: “At presentation, the visual acuity was 20/20 in each eye. Examination of his right eye showed conjunctival hyperemia without purulence and a normal anterior chamber and fundus. More than a dozen mobile, translucent larvae were observed on the cornea, bulbar conjunctiva, and upper and lower conjunctival fornices (Panel A, and see video)”.
Oestrus ovis (Diptera: Oestridae; nasal bot)
(Diptera: Oestridae; nasal bot) is described as a brownish fly around the same size as that of a honeybee. In most areas of the world, the fly is known to deposit its first-stage larvae in the nostrils of sheep. These microscopic larvae mature into maggots, also known as large bots. These maggots spend most of their larval stages in the nasal passages and sinuses. The persisting symptoms of larvae infestation in the nasal passages or sinuses generally include an obstructed nasal passage, inflammation and irritation.
The larvae once in a latter stage then drip to the ground and convert to flies. This life cycle of the parasite, where the living tissue is infested by the larvae is referred to as myiasis. However, the condition is primarily found in sheep. In some cases, it may also spread through spores and affect goats, dogs, and human beings, shepherds. The presence of larvae may also cause chronic irritation, sinusitis and mucopurulent rhinitis. According to studies, the bots can easily be found in exposed paranasal sinuses and nasal passages if the head is cut. In very rare cases, the larvae may also penetrate the cranial vault via the ethmoidal plate, which may result in direct or secondary bacterial meningitis.
Diagnosis and treatment
Diagnosing Oestrus ovis primarily depends on the demonstration of the microfilariae in the skin on conjunctival biopsies. If not treated timely, the treatment of heavily parasitized animals may lead to occlusion of the carotid arteries. Drugs commonly prescribed as first-line of treatment include “piperazine (100 to 300 mg/kg PO), diethylcarbamazine (100 mg/kg PO), and stibophen (5 to 10 mg/kg IM for 3 to 10 days)”.
Ocular presentation of nasal bots
The nasal bots, in some cases, can migrate to the nasolacrimal duct and enter the conjunctival sac. This leads to local inflammation, with symptoms of chemosis (eye irritation), hyperemia (excess of blood in the vessels) and epiphora (overflow of tears onto the face). Doctors diagnose the condition based on the presence of larvae in the conjunctival sac. Treatment includes moxidectin or eprinomectin. The larvae that are visible are removed mechanically using tweezers, as in this case. The nasal botfly is also known to cause conjunctival and corneal lesions in horses in South Aftica.
Source: Nicolas Abihaidar et al, External Ophthalmomyiasis Due to Oestrus ovis, New England Journal of Medicine (2022). DOI: 10.1056/NEJMicm2115416