Researchers from five nations reported a case of infection in an Englishwoman with a parasitic flatworm from the trematode class (flukes), which typically affects birds and less often mammals. The parasite, contracted probably during a trip to the Galapagos Islands, was found in the patient’s eye. The case description was published in the journal Emerging Infectious Diseases from the US Centers for Disease Control and Prevention (CDC).
Parasitic trematodes of the genus Philophthalmus are widespread globally and generally inhabit the conjunctival sacs of water birds, leading to their designation as avian ocular flukes. Their intermediate hosts are freshwater and marine snails. Birds become infested by ingesting parasite metacercariae encysted on algae. Due to warmth, they emerge from cysts in the pharynx and travel through the nasolacrimal ducts to the orbits, where they mature into adults. Besides birds, infection instances have been noted in capybaras (Hydrochoerus hydrochaeris), Galapagos sea lions (Zalophus wollebaeki), and, much more seldom, other mammals. Since 1939, only 12 instances of philophthalmiasis in humans have been documented—in Asia, Europe, and North America.
Thomas Weitzel from Charité University Hospital in Berlin, alongside colleagues from the USA, France, Chile, and Ecuador, detailed the situation of a 26-year-old Englishwoman who sought care in Santiago complaining of severe pain, swelling, and a feeling of a foreign object moving in her right eye over nine days. Before these symptoms emerged, she had visited Colombia (four weeks), Ecuador, including the Galapagos Islands where her sole contact with a natural water body occurred during the trip (2.5 weeks), and Peru (one week). During the ophthalmic examination, pronounced swelling of the eyelids and conjunctiva of the affected eye was observed, along with a follicular reaction of the lower conjunctival fornix and the upper eyelid cartilage conjunctiva. Examination of the cornea, anterior segment, and fundus revealed no abnormalities.
During a detailed inspection of the affected areas, physicians noticed an elongated, mobile structure on the conjunctiva of the upper eyelid cartilage and removed it with a moist cotton swab. After removal, the foreign body sensation ceased, and full recovery without complications occurred within a few weeks. Microscopic analysis of the extracted structure identified it as a single, mature, egg-producing specimen of the fluke Philophthalmus lacrymosus, exhibiting morphological and morphometric traits consistent with other described members of this species.
To confirm the species identification, researchers employed PCR and Sanger sequencing for the nuclear internal transcribed spacer 2 (ITS-2) and the mitochondrial cytochrome c oxidase subunit I (Cox1). The ITS-2 consensus sequence fully matched that of P. zalophi from the Galapagos sea lion, matched P. lacrymosus found in gulls in Portugal by 98.6 percent, matched P. lucipetus by 95.9 percent, matched P. gralli detected in invasive terrestrial snails (Melanoides tuberculata) in Costa Rica and small passerines in Peru by 95.6 percent. The Cox1 consensus sequence matched that of Dominican gulls (Larus dominicanus) from Brazil by 99.45 percent, and matched P. lacrymosus samples from Portugal by 91.90–92.15 and 87.34–87.09 percent.
The findings from the clinical and epidemiological study suggest that the zoonotic ocular fluke P. lacrymosus can affect humans in South America (in this case, infection most likely occurred in the Galapagos Islands). They also indicate the possibility that P. zalophi may be conspecific with P. lacrymosus, and that some morphological differences between them might be due to adaptation to a new host when switching from birds to sea lions.
Previously, physicians had documented cases of finding a parasitic crustacean (the pentastomid Armillifer grandis) in the eye of a resident of the Democratic Republic of Congo, who was infected after eating crocodile meat, and cases of brain and eye infection in two American boys caused by raccoon roundworms, Baylisascaris procyonis.
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