Detection of Thelazia callipaeda in Phortica variegata and spread of canine thelaziosis to new areas in Spain

Background: The fruit fly Phortica variegata (Drosophilidae: Steganinae) feeds on the ocular secretions of animals and humans, and has been described as an intermediate host of the eye worm Thelazia callipaeda (Spirurida: Thelaziidae) in Italy. Despite the increased detection of T. callipaeda in many European countries, information about its vector role in natural conditions is still limited. In the Iberian Peninsula, thelaziosis caused by T. callipaeda has been reported in dogs, cats, red foxes, wild rabbits and humans. Methods: In the last seven years, we have detected increased numbers of cases of canine thelaziosis at three locations in mainland Spain: Site 1, La Vera region (Caceres Province, central-western Spain; 51 cases); Site 2, El Escorial municipality (Madrid Community, central Spain; 23 cases); and Site 3, Miraflores de la Sierra municipality (Madrid Community, central Spain; 41 cases). Site 1 is considered endemic for T. callipaeda while the other two sites have been recently recognised as risk zones for T. callipaeda infection. Results: From June 2016 to September 2017, 2162 flies were collected and morphologically identified as Phortica spp. (Site 1, n = 395; Site 2, n = 1544; and Site 3, n = 223). Upon dissection, third-stage T. callipaeda larvae were found in two out of 155 flies examined from Site 1, and both these larvae tested molecularly positive for the eye worm. Of the 395 flies collected from Site 1, 371 were molecularly processed for arthropod species identification and T. callipaeda detection. All 371 flies were identified as P. variegata and 28 (7.5%; 95% CI: 4.8-10%) tested positive for T. callipaeda DNA haplotype 1. Conclusions: Our findings indicate that T. callipaeda circulates among dogs and P. variegata in Spain, where zoonotic cases have been also reported. The co-existence of canine thelaziosis and Phortica spp. in geographical areas previously considered free of the eye worm indicates a risk of infection for both animals and humans living in this region.