First Report of Human Thelazia Infection in Madrid: A Pediatric Case

To the Editors: In November 2024, a 2-year-old child attended the Pediatric Emergency Department of Puerta de Hierro University Hospital (Majadahonda) with a 5-day history of conjunctival irritation and tearing, previously treated with antibiotic eye drops for 2 days. Symptoms worsened, including mild conjunctival erythema, discharge, pain, pruritus, fever for 24 hours, nasal congestion and decreased oral intake. The patient had been followed for 5 months for recurrent ocular irritation and intermittent discharge, initially diagnosed as allergic conjunctivitis. Epidemiologically, the child lived in a rural area in the Guadarrama mountains, had contact with animals and attended nursery school. Ophthalmologic examination re-vealed a normal right eye and a hyperemic left conjunctivae with marked tarsal papillary reaction. Two helminths with macroscopic resemblance to pinworm larvae were observed in the left eye. The parasites were extracted and sent to the Microbiology Department for etiologic diagnosis after ruling out perianal pinworm infestation. Diagnosis was established by direct microscopic observation. The nematodes showed morphologic characteristics consistent with female adult Thelazia callipaeda. The wall of the nematodes was finely striated and showed the characteristic deep buccal capsule (Fig. 1A). The specimen showed a protruding vulvar opening anterior to the esophagus–intestinal junction (Fig. 1B) and multiple coiled first instar larvae (Fig. 1C). Molecular confirmation was performed by polymerase chain reactin amplification and sequencing of the mitochondrial cytochrome oxidase subunit 1 (CO1) gene, identifying the parasite as haplotype 1, the only haplotype described in animals and humans in Europe.FIGURE 1.: A: Apical portion of two Thelazia callipaeda specimens showing the distinctive buccal cavity and the cuticle with transverse striations. B: Medium portion of the body showing numerous coiled larvae. C: Protruding vulvar opening anterior to the esophagus–intestinal junction of the specimen.Following parasite extraction, the patient continued treatment with antibiotic eye drops for 1 week, supplemented with corticosteroid and antihistamine eye drops. Symptoms resolved within 7 days. Since the 21st century, human cases of ocular thelaziosis in Europe have increased, with 11 cases reported between 2001 and 2020 across several countries, including Spain.1 This rise is linked to animal reservoirs, particularly wild canids such as red foxes and wolves, which play a key role in maintaining and spreading the parasite. Their ecological overlap with the vector and proximity to humans and domestic animals facilitate zoonotic transmission.2 The arthropod vector, Phortica variegata (Drosophila genus), shows attraction to the eye secretions of humans and some animals. This contributes to their role as vectors in this parasitosis. In Spain, the first canine case was reported in 2010 in Cáceres. Since then, cases have expanded significantly, with infections documented in 19 provinces and high prevalence rates, especially in regions like La Vera and El Escorial. Spain is now considered endemic for canine thelaziosis, increasing the risk of human infection.3 The first human case in Spain was reported in 2012, followed by 6 more cases in the geographic areas of Cáceres, León, Ourense, Madrid and Salamanca.4 Despite the high prevalence in animals, this represents the first reported human ocular thelaziosis case in the Community of Madrid. Given the increasing number of animal cases, further human infections are expected. This case highlights the importance of including ocular thelaziosis in the differential diagnosis of patients with conjunctival symptoms, particularly in those with rural exposure or contact with animals in endemic areas. ACKNOWLEDGMENTS We thank Ana Hernández-González, Esther Rodríguez and Lourdes Castro, and the colleagues from the Microbiology and Ophthalmology Departments for their technical and clinical advice.