Volume 29, Number 4—April 2023
Prevention of Thelazia callipaeda Reinfection among Humans
Thelazia callipaeda is a zoonotic vector-borne nematode that infects and causes eye disease among a wide range of domestic and wild mammals, including humans. We describe an unusual case of reinfection by this nematode in Serbia and call for a focus on preventive measures in endemic areas.
The genus Thelazia (order Spirurida, family Thelaziidae) comprises several species of nematode that cause ocular infections in different host mammals, including humans (1). Over the past 20 years, the T. callipaeda eyeworm has gained interest among the scientific community because several human cases have been reported in countries in Asia and Europe, making this parasite an agent of public health concern (1). Adult and larval forms of T. callipaeda eyeworms infect the ocular apparatus of a wide range of both domestic (e.g., dogs, cats) and wild (e.g., red foxes, wolves, jackals, bears, lagomorphs) animal species, including humans (1–3). In Europe, 2 species of drosophilid fruit flies were confirmed to act as vectors of T. callipaeda eyeworms: Phortica variegata, tested under laboratory and natural conditions (4), and P. oldenbergi only experimentally (5). Thelaziosis should be expected among humans in areas where T. callipaeda infection is endemic in animal reservoirs. Absence of preventive measures could be a factor influencing human reinfections in endemic areas. We describe a case of T. callipaeda reinfection in a human patient and call for focus on prevention in areas where the parasite and its vectors thrive.
A man, 41 years of age, living in a small village in the southern part of Serbia contacted an ophthalmologist at the University Clinical Center in Nis, Serbia, because of ocular discomfort. The patient reported a history of clinical thelaziosis caused by T. callipaeda infection 5 years earlier. Ophthalmic manifestations were conjunctivitis with increased lacrimation, itching, and sensation of a foreign body in his left eye. During ophthalmologic examination, we removed 11 eyeworms (6 female, 5 male) from the eye and subsequently identified them morphologically as T. callipaeda according to an identification key (6). The nematodes had a filariform body type with a transversally striated cuticle and a buccal capsule of hexagonal shape. Among female worms, the vulva was located anterior to the esophagus-intestinal junction; male worms had a curved caudal end with 2 asymmetric spicules and precloacal and postcloacal papillae (Table; Figure).
To confirm morphologic identification, we extracted genomic DNA from individual worms using a QIAGEN DNeasy Blood & Tissue Kit (https://www.qiagen.com), and performed PCR analysis using the primers NTF (5′-TGATTGGTGGTTTTGGTAA-3′) and NTR (5′-ATAAGTACGAGTATCAATATC-3′), which amplify a 689-bp portion of the mitochondrial cytochrome c oxidase subunit 1 (cox1) gene. We purified amplified DNA products and sequenced them in both directions using ThermoFisher Big Dye Terminator version 3.1 chemistry in an Applied Biosystems 3130 genetic analyzer with an ABI-PRISM 377 automated sequencer (https://www.thermofisher.com). We analyzed sequences using MEGA version 7 software (https://www.megasoftware.net) and compared them with those available in GenBank using BLAST (https://blast.ncbi.nlm.nih.gov/Blast.cgi). Nucleotide sequences had 100% identity with T. callipaeda (GenBank accession no. AM042549.1). In addition, phylogenetic analysis performed by using the maximum-likelihood method based on the Tamura-Nei model showed the representative sequence from our study clustered with other sequences of T. callipaeda belonging to haplotype 1 (Appendix), the only haplotype thus far described in Europe. We deposited the nucleotide sequence in GenBank (accession no. OP696980).
We treated the patient with topical antimicrobials and corticosteroids (rinsing with 3% boric acid 5×/d and topical tobramicin/deksametazon 5×/d). At clinical follow-up 7 and 14 days later, we found no signs or symptoms of eye infection.
T. callipaeda eyeworm prevalence in humans and animals has increased throughout Europe in recent decades (1). To date, human thelaziosis has been described in 12 patients from Europe, including a case-patient in Serbia (7) reinfected by T. callipaeda eyeworms 5 years after an initial case, as in the case we describe here. A related study called for implementing preventive measures, such as vector control and treatment of domestic reservoirs (e.g., dogs), to avoid zoonotic human infection (8). In addition, wild carnivore reservoirs, such as red foxes and wolves, should be considered as sources of infection for humans who frequent the same forest areas (9). The patient in our study reported that he spent long periods picking mushrooms in the forest, and he exhibited clinical manifestations of thelaziosis during the summer (July), when outdoor activities are most common and the P. variegata fruit fly, a T. callipaeda eyeworm vector, is most abundant.
Reinfection in this patient highlights that T. callipaeda eyeworms can cause recurrent infection in human hosts, which suggests the potential usefulness of implementing prevention and control strategies in the Balkan Peninsula, where this parasite and its vector and animal reservoirs are spreading (10). Moreover, it indicates that inspecting for T. callipaeda eyeworms should be part of routine periodic examinations in endemic areas, even among asymptomatic persons.
Dr. Trenkić is an assistant professor in the medical faculty, Department of Ophthalmology, University of Niš. She performs ophthalmologic research.
The authors thank Riccardo Paolo Lia for his support on morphologic identification and Giada Annoscia for her support on molecular analysis.
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TableCite This Article
Original Publication Date: March 18, 2023
Table of Contents – Volume 29, Number 4—April 2023
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Domenico Otranto, University of Bari Aldo Moro, Strada provinciale per Casamassima km3, 70010 Valenzano, Italy