Occurrence of Thelazia callipaeda and its vector Phortica variegata in Austria and South Tyrol, Italy, and a global comparison by phylogenetic network analysis

Abstract

The zoonotic nematode Thelazia callipaeda infects the eyes of domestic and wild animals and uses canids as primary hosts. It was originally described in Asia, but in the last 20 years it has been reported in many European countries, where it is mainly transmitted by the drosophilid fruit fly Phortica variegata. We report the autochthonous occurrence of T. callipaeda and its vector P. variegata in Austria. Nematodes were collected from clinical cases and fruit flies were caught using traps, netting, and from the conjunctival sac of one dog. Fruit flies and nematodes were morphologically identified and a section of the mitochondrial cytochrome c oxidase subunit I gene (COI) was analysed. A DNA haplotype network was calculated to visualize the relation of the obtained COI sequences to published sequences. Additionally, Phortica spp. were screened for the presence of DNA of T. callipaeda by polymerase chain reaction. Thelazia callipaeda and P. variegata were identified in Burgenland, Lower Austria, and Styria. Thelazia callipaeda was also documented in Vienna and P. variegata in Upper Austria and South Tyrol, Italy. All T. callipaeda corresponded to haplotype 1. Twenty-two different haplotypes of P. variegata were identified in the fruit flies. One sequence was distinctly different from those of Phortica variegata and was more closely related to those of Phortica chi and Phortica okadai. Thelazia callipaeda could not be detected in any of the Phortica specimens.

Keywords: COI; Canine thelaziosis; Cytochrome c oxidase subunit I; Emerging zoonotic disease; Oriental eye worm; Vector-borne disease; Zoophilic fruit fly.

Fig. 1

Geographical distribution of sampling sites for Phortica variegata and location of the residence of the infected animal, or if not available, that of the clinic of the treating veterinarian of clinical cases of Thelazia callipaeda included in this study. BL Burgenland, CA Carinthia, LA Lower Austria, SZ Salzburg, ST South Tyrol, SY Styria, TY Tyrol, UA Upper Austria, VI Vienna, VB Vorarlberg. [Map created using QGIS v.3.22.3 (Free Software Foundation, Boston, MA)]

Fig. 2

Median-joining haplotype network of the cytochrome c oxidase subunit I gene (COI) sequences (617 nucleotide positions) of Thelazia callipaeda showing the geographical distribution (a) and the reported hosts (b). Circles represent haplotypes; numbers within the circles represent the number of individuals; if no number is shown, then only one individual is represented. Representative GenBank accession numbers of the haplotypes are shown next to the circles; white circles represent intermediate nodes; bars on branches connecting haplotypes represent the number of substitutions; asterisks indicate haplotypes of the individuals obtained in the present study

Fig. 3

Median-joining haplotype network of the COI sequences (647 nucleotide positions) of Phortica variegata sensu stricto (a) and Phortica spp. closely related to the unknown specimen from the present study (b) showing the geographical distribution. Circles represent haplotypes; numbers within the circles represent the number of individuals; if no number is shown, then only one individual is represented. Representative GenBank accession numbers of the haplotypes are shown next to the circles; white circles represent intermediate nodes; bars on branches connecting haplotypes represent the number of substitutions; asterisks indicate haplotypes of the individuals obtained in the present study