Answer to November 2022 Photo Quiz

Abstract

Read the full article for the answer.

INTRODUCTION

The adult specimen was subsequently identified as a female Thelazia callipaeda. Adult nematode size, the presence of cuticles along the periphery, larval deposition through the vulva, shape of buccal cavity, and presence of anterior pore at the esophageal-intestinal junction were all identifying characteristics of this species (1, 2).

Initial suspicion by ophthalmologists, after appearance of the specimen in the eye, was an adult Loa loa. However, Loa loa is found normally in the subconjunctiva, and the size of adult forms is from 4 to 7 cm (3). Moreover, the blood PCR performed had a negative result for microfilariae species. The size of Dirofilaria spp. adults ranges from 10 to 70 cm. Dirofilaria spp. have longitudinal cuticular ridges that were not presented on our specimen (4). With respect to Gnathostoma spp., 2- to 3-cm larvae (L3) are the only form found in humans. These possess a cuticular armature of the body surface and a cephalic bulb with seven or eight rows of spines depending on the species; the vulva in females is located ventrally in the posterior third of the body (5). Sparganosis (genus Spirometra) is a larval cestodiasis that accidentally parasitizes humans through plerocercoid larvae (6). Our adult nematode presented a defined alimentary canal, the presence of larvae in the uterus, and a cuticle around the body that is absent in larvae of Spirometra species.

Ocular thelaziosis is a zoonosis in canids, felids, and cattle (2, 7). Known as “Oriental eye worm”, Thelazia callipaeda was introduced in Europe in 2000, and the first case was reported in the north of Italy (8). The lacrimophagous male fly Phortica variegata is the primary vector in Europe (7, 8). Since the first human thelaziosis case in Cáceres, Spain, in 2011, ocular thelaziosis has represented an emerging zoonosis in our country but may be underdiagnosed (2, 9).

The cycle starts when the fly contacts the lacrimal secretions of mammalian animals such as dogs, red foxes, cows, cats, or hares during the spring/summer season. After ingestion of eggs or noninfective larvae (L1), two moults to infective larvae (L3) occur inside the fly. After contact of the fly with the lacrimal apparatus of these animals or humans, the L3 larvae develop into adults in approximately 35 days (7).

Human cases may be asymptomatic. Clinical infection is localized in the eye without systemic response. The most common symptom is a foreign body sensation, as our patient presented (8). The adult is usually found in the lacrimal apparatus under the lids or on the conjunctiva, nasolacrimal ducts, conjunctival sacs, or excretory ducts of the lachrymal glands (7). Other cases have occurred during phacoemulsification cataract surgery in elderly patients while performing slit lamp biomicroscopy of the eye as in our case (10). Thelazia spp. can cause conjunctivitis, hypermia, keratitis, or corneal ulceration due to the outer cuticle of the nematode (10). Treatment consists of removing the adult without the need of pharmacological treatment (7). Our patient received 7 days of eye drops with moxifloxacin (three times per day) to avoid bacterial superinfection (10).