From June 2005 through August 2006, a total of 4 patients with human thelaziasis were referred to the Department of Emergency and Admissions at Croce and Carle Hospital in Cuneo, Italy, for consultation. The 4 male patients (age range 37–65 years) lived in northwestern Italy (43°N, 6°E) and southeastern France (46°N, 9°E), where infections had been reported in dogs, cats, and foxes (9,12). All patients had similar symptoms (exudative conjunctivitis, lacrimation, and foreign body sensation) for a few days to weeks before referral (Table). All patients required medical attention during the summer (June–August 2005 and 2006) and reported floating filaments on the eye surface. A medical history was obtained for 3 of the patients. The other patient (patient 2, a homeless man) was referred to a physician at the local social services in Nice, France, for severe mental disorders, poor hygiene, and diabetes (Table). Infections in patient 2 were diagnosed 1 month apart in each eye (June and July 2005; referred to as patient 2a and 2b). None of the patients had had any eye disease or had traveled outside their area of residence, with the exception of patient 1 who had gone trekking in the woods in Tenda (Piedmont region, Italy) ≈3 weeks before the onset of symptoms.

Eye examinations showed thin, white nematode(s) on the conjunctival fornix of the affected eye. Nematodes were removed with a forceps after local anesthesia (1% novocaine) was administered. The nematodes were stored in 70% ethanol until they were morphologically identified and analyzed. After the parasites were removed from the eyes, antimicrobial eye drops were prescribed for ≈7 days. Ocular symptoms disappeared within 2–3 days.

Collected nematodes were identified based on morphologic keys (13,14). T. callipaeda nematodes have a serrated cuticle (Figure 2, panel A), buccal capsule, mouth opening with a hexagonal profile, and 6 festoons. Adult females are characterized by the position of the vulva, located anterior to the esophagus-intestinal junction, whereas males have 5 pairs of postcloacal papillae. To confirm morphologic identification, specimens from patients 2 and 4 were analyzed as previously described (11). Genomic DNA was isolated from each nematode, and a partial sequence of the mitochondrial cytochrome c oxidase subunit 1 (cox1, 689 bp) gene was amplified by PCR. Amplicons were purified by using Ultrafree-DA columns (Amicon; Millipore, Bedford, MA, USA) and sequenced by using an ABI-PRISM 377 system and a Taq DyeDeoxyTerminator Cycle Sequencing Kit (Applied Biosystems, Foster City, CA, USA). Sequences were determined in both directions and aligned by using the ClustalX program (15). Alignments were verified visually and compared with sequences available for the cox1 gene of T. callipaeda (GenBank accession nos. AM042549–556).

A total of 6 adult nematodes were morphologically identified as T. callipaeda (Table). A mature female nematode (patient 4) had embryonated eggs in the proximal uterus and larvae in the distal uterus (Figure 2, panel B). This suggested that a male worm was present, which had been rubbed out of the eye before symptoms occurred or had remained undetected. Sequences obtained from nematodes were identical to the sequence of haplotype 1 of T. callipaeda (GenBank accession no. AM042549) (11).

We report human infection by T. callipaeda in Italy and France in the same area where canine thelaziasis had been reported. These infections highlight the importance of including this arthropod-borne disease in the differential diagnoses of bacterial or allergic conjunctivitis. All cases of human thelaziasis were reported during the summer months (June–August), which is the period of T. callipaeda vector activity (late spring to fall in southern Europe) (7). The seasonality of human thelaziasis may impair correct etiologic diagnosis of this disease because spring and summer are the seasons in which allergic conjunctivitis (e.g., by pollens) occurs most frequently. This finding is particularly important when infections are caused by small larval stages that are difficult to detect and identify. Furthermore, clinical diagnosis of human thelaziasis is difficult if only small numbers of nematodes are present because clinical signs related to an inflammatory response mimic allergic conjunctivitis, especially when they are associated with developing third- or fourth-stage larvae.

Untimely or incorrect treatment of the infection may result in a delay in recovery, mainly in children and the elderly, who are most likely to be exposed to infection by the fly. Although treatment for canine infection with T. callipaeda with topical organophosphates, 1% moxidectin, or a formulation containing 10% imidacloprid and 2.5% moxidectin is effective, mechanical removal of parasites in humans remains the only curative option (3). Thus, prevention of human thelaziasis should include control of the fly vector by use of bed nets to protect children while they are sleeping and by keeping their faces and eyes clean. Genetic identification of haplotype 1 has shown that this is the only haplotype circulating in animals (i.e., dogs, cats, and foxes) in Europe (11). This finding confirms the metazoonotic potential of Thelazia spp. infection and the need to treat infected domestic animals, which may act as reservoirs for human infection.