Systematic review on infection and disease caused by Thelazia callipaeda in Europe: 2001-2020

New host record of Thelazia callipaeda (Nematoda: Spirurida) with a notably wide host range and shared zoonotic lineage in Japan

Thelazia callipaeda (Nematoda: Spirurida: Thelaziidae) parasitizes the eyes of dogs, cats, humans, and various wild mammals, and is transmitted by drosophilid flies. In Japan, T. callipaeda is considered an emerging parasite that has expanded its endemic region northward. However, reports of its detection in mammals other than domestic animals and humans are scarce. This study reports the detection of T. callipaeda in Japanese red fox (Vulpes vulpes japonica), masked palm civet (Paguma larvata), Japanese badger (Meles anakuma), Japanese black bear (Ursus thibetanus japonicus), raccoon (Procyon lotor), Japanese raccoon dog (Nyctereutes viverrinus), domestic dog (Canis lupus familiaris), domestic cat (Felis silvestris catus), and human. Of these, the Japanese red fox, masked palm civet, Japanese badger, and Japanese black bear have been reported as novel host records. Sequence analysis of the cytochrome c oxidase subunit I gene of T. callipaeda revealed two unique lineages specific to Japan, with no regional or host species differences. These results suggest a wide host range for T. callipaeda, highlighting the significant role of wildlife as a reservoir for this parasite in Japan.

Emergence of Thelaziosis Caused by Thelazia callipaeda in Dogs and Cats, United States

We report 2 autochthonous feline thelaziosis cases caused by the eyeworm Thelazia callipaeda and discuss the spread among dogs in the northeastern United States. Phylogenetic analysis suggests the parasite was introduced from Europe. Adopting a One Health approach is needed to limit further spread of T. callipaeda eyeworms in North America.

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

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.

Ocular thelaziosis: an emerging human parasitosis in Europe

Ocular thelaziosis is a parasitosis distributed mainly in East Asia, but increasingly described in Europe in different domestic and wild animals, including dogs, different wild canids and lagomorphs, and exceptionally in humans. In Spain, in some areas, a high infection prevalence rate has been described in domestic canids, which may lead to an increase in human cases. However, the description of human cases is still exceptional, which suggests that they are probably underdiagnosed. A case of ocular thelaziosis in a 2-year-old girl from an urban environment is described.

Wild Mesocarnivores as Reservoirs of Endoparasites Causing Important Zoonoses and Emerging Bridging Infections across Europe

Mesocarnivores are small- or mid-sized carnivore species that display a variety of ecologies and behaviours. In Europe, wild mesocarnivores are represented by the red fox (Vulpes vulpes), the golden jackal (Canis aureus), the European wildcat (Felis silvestris), the Mustelidae of the genera Meles, Martes, Mustela, Lutra, the invasive species of raccoon dog (Nyctereutes procyonoides), raccoons (Procyon lotor), and American mink (Neogale vison). These abundant animals thrive in various habitats and often develop their activity close to human settlements. Thus, they may play an important role in the introduction, maintenance, and transmission of major parasitic zoonoses and promote bridging infections with domestic animals. Against this background, this article reports and discusses some of the most important endoparasites of wild mesocarnivores living in Europe, on the basis of their actual role as reservoirs, spreaders, or sentinels. The data derived from epizootiological studies in different European countries, and the proven or speculated implications of the detected endoparasites in human and domestic animals' health, are discussed. Through older and recent literature review, the state-of-the-art knowledge on the occurrence and prevalence of the parasites under consideration is presented, showing further, warranted investigations and the need for surveillance and vigilance.

Human Thelaziosis Caused by Thelazia callipaeda Eyeworm, Hungary

Ocular infections with Thelazia callipaeda eyeworms in Europe have become more common. We report a case in Hungary caused by T. callipaeda eyeworms in a 45-year-old woman who had no travel history abroad.

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European Hares, Lepus europaeus, Represent a Reservoir Host for Thelazia callipaeda in Romania

Thelaziosis caused by Thelazia callipaeda is an emerging disease in Europe. Only two reports of naturally infected lagomorphs have been published so far. The aim of this study was to evaluate the status of the Romanian populations of European brown hares, Lepus europaeus as reservoir hosts for T. callipaeda. Between November 2019 and November 2021, the eyes of 326 L. europaeus carcasses were examined for the presence of ocular parasites. Nematodes were stored in plastic vials with physiological saline, followed by morphological and molecular identification. QGis 3.20 and EpiInfoTM 7 were used for mapping and statistical analysis. Four (1.23%) hares harbored T. callipaeda infection, with a total of 84 nematodes collected (mean intensity 21 nematodes/host), with 45 males, 39 females (two sexually immature, seven with only eggs, and 30 with eggs and larvae). One specimen from each host was successfully sequenced resulting in a 100% similarity with several other sequences of T. callipaeda haplotype 1. Statistical analysis revealed no significant results. The current study represents a first report of T. callipaeda in the European brown hare in Romania, and the second in Europe, also reiterating the role of lagomorphs as reservoir hosts for this zoonotic ocular nematode.

Efficacy of a formulation of sarolaner/moxidectin/pyrantel (Simparica Trio®) for the prevention of Thelazia callipaeda canine eyeworm infection

Background

For a long time known as the oriental eyeworm, Thelazia callipaeda is a zoonotic nematode that infects the eyes of a wide range of vertebrate hosts including dogs, cats, wildlife carnivores, lagomorphs, and humans. The high occurrence of this infection in Europe and the first cases in the United States have increased scientific interest in the parasite, as it also represents a risk for people living in endemic areas. Therefore, treatment and prevention of thelaziosis in canine population are advocated to reduce the risk of human infection as well. Here, we assessed the efficacy of a formulation containing sarolaner/moxidectin/pyrantel (Simparica Trio^®) administered orally at monthly intervals, for the prevention of establishment of infection with T. callipaeda in naturally infected dogs. In this formulation, moxidectin is expected to have efficacy against eyeworms, whereas sarolaner and pyrantel are not.

Methods

The study was conducted in eyeworm endemic areas of Italy and France, where dogs (n = 125) were assigned into two groups consisting of a negative control group (G1; n = 62), in which animals were treated monthly with a control product (sarolaner; Simparica^®), and a treatment group (G2; n = 63) in which animals were treated monthly with Simparica Trio (sarolaner/moxidectin/pyrantel) from day 0 to day 150. In total, nine animals were withdrawn from the study (two animals became positive at day 30, and seven for reasons unrelated to eyeworm infection), resulting in 116 animals (n = 58 for G1; n = 58 for G2).

Results

In G1, 16 out of 58 animals (27.6%) were observed with eyeworms during the study, and none of the animals from G2 were ever observed with eyeworms, resulting in 100% efficacy (P < 0.0001) in the prevention of establishment of T. callipaeda infection. Adult nematodes and fourth-instar (L4)-stage larvae were recovered from the eyes of positive animals, counted, and morphologically identified as T. callipaeda. In addition, specimens from Italy were molecularly confirmed as belonging to the haplotype 1 (i.e., the only one circulating in Europe so far).

Conclusions

Data presented herein demonstrated 100% efficacy of Simparica Trio for the prevention of T. callipaeda eyeworm infection in dogs from highly endemic areas of France and Italy. The use of this formulation is advantageous, as it is a licensed product in Europe with a wide efficacy spectrum against other nematodes, multiple tick species, and fleas. In addition, preventing the development of infection in dogs could also be a prophylaxis measure for zoonotic T. callipaeda infection in humans inhabiting endemic areas.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-022-05501-6.

First report of human Thelazia callipaeda infection in Portugal

The zoonotic parasitic nematode Thelazia callipaeda, also known as the oriental eye worm, is endemic in several European countries, including Portugal. Infections may result in ocular disease in domestic and wild animals as well as humans, with more or less severe manifestations. We report the first human case of ocular thelaziosis by T. callipaeda in Portugal, a country where the parasite had already been found to infect dogs, cats, red foxes, wild rabbits and a beech marten. An 80-year-old patient from east-central Portugal, who had been suffering from tearing for a few years, had whitish filiform fragments removed from the left eye. Polymerase chain reaction of partial cytochrome c oxidase subunit 1 and 18S small subunit rRNA genes followed by bidirectional sequencing and BLAST analysis confirmed T. callipaeda haplotype 1, the only haplotype previously reported in Europe. The endemicity of T. callipaeda in domestic and wild animals in east-central Portugal makes it very likely that infection of the human patient had occurred locally. In east-central and other geographical areas of Portugal, veterinarians and physicians, especially ophthalmologists, should regard T. callipaeda as a cause of ocular pathology in animals and humans.

Laboratory breeding of two Phortica species (Diptera: Drosophilidae), vectors of the zoonotic eyeworm Thelazia callipaeda

Background

Some species of drosophilid flies belonging to the genus Phortica feed on ocular secretions of mammals, acting as biological vectors of the zoonotic eyeworm Thelazia callipaeda. This study describes an effective breeding protocol of Phortica variegata and Phortica oldenbergi in insectary conditions.

Methods

Alive gravid flies of P. oldenbergi, P. variegata and Phortica semivirgo were field collected in wooded areas of Lazio region (Italy) and allowed to oviposit singularly to obtain isofamilies. Flies were maintained in ovipots (200 ml) with a plaster-covered bottom to maintain high humidity level inside. Adult feeding was guaranteed by fresh apples and a liquid dietary supplement containing sodium chloride and mucin proteins, while larval development was obtained by Drosophila-like agar feeding medium. The breeding performances of two media were compared: a standard one based on cornmeal flour and an enriched medium based on chestnut flour. All conditions were kept in a climatic chamber with a photoperiod of 14:10 h light:dark, 26 ± 2 °C and 80 ± 10% RH.

Results

From a total of 130 field-collected Phortica spp., three generations (i.e. F1 = 783, F2 = 109, F3 = 6) were obtained. Phortica oldenbergi was the species with highest breeding performance, being the only species reaching F3. Chestnut-based feeding medium allowed higher adult production and survival probability in both P. oldenbergi and P. variegata. Adult production/female was promising in both species (P. oldenbergi: 13.5 F1/f; P. variegata: 4.5 F1/f).

Conclusions

This standardized breeding protocol, based on controlled climatic parameters and fly densities, together with the introduction of an enriched chestnut-based feeding medium, allowed to investigate aspects of life history traits of Phortica spp. involved in the transmission of T. callipaeda. Obtaining F3 generation of these species for the first time paved the road for the establishment of stable colonies, an essential requirement for future studies on these vectors in controlled conditions.

Graphical abstract

Wild carnivores and Thelazia callipaeda zoonotic eyeworms: A focus on wolves

Thelazia callipaeda is a zoonotic parasite causing ocular disease in domestic dogs, cats, several wild carnivores, hares, and humans. This nematode is widely distributed in Europe, where it is transmitted by the drosophilid fly Phortica variegata. Since the first report of infection in grey wolves (Canis lupus) from southern Italy, other cases of thelaziosis have been recorded in this animal species throughout Europe, raising questions about their role in spreading T. callipaeda. Indeed, for their wandering behavior through long distances and living in woody areas where the vectors thrive, wolves may act as reservoirs and spreaders of thelaziosis. In this study we reviewed the literature about wolves acting as reservoirs of T. callipaeda in Europe. In addition, we report the first detection of T. callipaeda eyeworms in grey wolves in the Italian Alps, discussing its possible implications in the epidemiology of thelaziosis in the Alpine landscape. Animals (n = 3) included in this study were originated from the Italian Alps, one juvenile male wolf was found dead, and the other two were seven-year-old males translocated from Piedmont region to a Zoological Garden, in Tuscany. All animals were infected with eyeworms, which were morphologically and molecularly identified as T. callipaeda. Data herein presented confirm those available in the literature about the circulation of a unique cox1 haplotype in Europe. In addition, the report of T. callipaeda in wolves from the Alps suggests an ecological continuity of habitats which are suitable for the distribution of T. callipaeda from the southern to northern Italy through the Apennine backbone. Retrospectively, it could also explain the spreading of the oriental eyeworm infection in Europe over the last 20 years with many wild carnivores, such as foxes and possibly wolves, playing a pivotal role as reservoirs of the infection for dogs, cats and humans.

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Wolves may play important role in the transmission cycle of Thelazia callipaeda.

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There is a need of passive-surveillance programs of this zoonotic nematode in wild carnivores.

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This is the first report of Thelazia callipaeda in wolves from the Italian Alps.

Development of Novel Management Tools for Phortica variegata (Diptera: Drosophilidae), Vector of the Oriental Eyeworm, Thelazia callipaeda (Spirurida: Thelaziidae), in Europe

Lachryphagous males of Phortica variegata (Fallén, 1823) are gaining increasing attention in Europe, as they act as vectors of the nematode Thelazia callipaeda Railliet & Henry, 1910, causal agent of thelaziosis, an emergent zoonotic disease. Currently, there are no effective control strategies against the vector, and surveillance and monitoring rely on time-consuming and nonselective sampling methods. Our aim was to improve the knowledge about the population dynamics and the chemical ecology of the species. A total of 5,726 P. variegata flies (96.4% males and 3.6% females, mostly gravid) were collected in field experiments during June-September of 2020 in an oak forest in northern Spain. Our results indicate that 1) by means of sweep netting a significantly higher number of captures were found both around the collector´s body and in the air than at ground level; 2) a positive relationship was detected between the abundance of Phortica flies and temperature, with two significant peaks of abundance at 24 and 33°C; 3) the blend of red wine and cider vinegar was the most attractive bait; 4) yellow traps captured fewer flies compared to black and transparent traps; and 5) a significant reduction toward vinegar and wine was detected in presence of the phenolic monoterpenoid carvacrol. In addition, all the males (n = 690) analyzed by both molecular detection and dissection resulted negative for the presence of T. callipaeda larvae. Overall, these findings provide a better understanding of the vector in terms of monitoring and management strategies.

Thelazia callipaeda in Slovakia - From sporadic cases to endemic areas

Spirurid nematode Thelazia callipaeda, transmitted by the fruit fly Phortica variegata, is a causative agent of an ocular parasitic disease called also canine thelaziosis. Dogs, cats, and wild canids are considered the primary definitive hosts for the parasite, but humans may also serve as aberrant definitive hosts. For long decades the geographic range of T. callipaeda was strictly limited to the territory of Asia, but after the year 2000, the parasite began to spread rapidly through Europe. The first autochthonous infections of dogs and foxes in Slovakia were recorded in 2016. In the present study, the results of a whole-area surveillance for canine thelaziosis are reported. Altogether, 142 cases of infection caused by T. callipaeda were diagnosed by veterinarians in dogs between 2016 and the first quarter of 2021, and two cases of feline thelaziosis were recorded. The majority of the dogs showed mild ocular signs manifested by conjunctivitis; 8.5% of them suffered from more serious mucopurulent discharge, and in two dogs corneal ulceration was recorded. The screening revealed increasing trends in the occurrence of canine thelaziosis from both a temporal and spatial point of view and unambiguously confirms the endemic status of T. callipaeda in Slovakia with the prospect of its further expansion.

Ocular thelaziosis: A case report of an emerging zoonosis

PURPOSE

To describe an unusual case of ocular thelaziosis due to Thelazia callipaeda, an underdiagnosed and emerging zoonosis.

OBSERVATIONS

We report an 81-year-old woman presented to our emergency department with a week long history of bilateral redness and tearing that had not improved despite antibiotics and corticosteroid topical treatment. Slit-lamp biomicroscopy showed signs of bilateral conjunctivitis and mucopurulent discharge in fornices. Under the upper tarsal conjunctiva of the left eye, two filiform worms were identified, which were removed and sent on wet mount slides for microscopic examination and genetic identification. The rest of the ophthalmoscopic examination was rigorously normal. Polymerase chain reaction (PCR) assay turned positive for Thelazia callipaeda. During further questioning, the patient reported that she had been on summer vacation in contact with dogs which were infected with eye worms.

CONCLUSIONS AND IMPORTANCE

Ocular thelaziosis is an emerging zoonosis in Spain, but also in the rest of the world. Ophthalmologists should include ocular thelaziosis in humans as a possible cause of conjunctivitis, tearing, and corneal ulcer, thus avoiding underdiagnosis and inappropriate treatments. The epidemiology of the disease makes anamnesis essential. A confocal biomicroscopy is a useful device for identifying this eyeworm but the definitive diagnosis will be made taking into account the morphological identification under microscope, together with the molecular identification by PCR techniques.

The Vector-Borne Zoonotic Nematode Thelazia callipaeda in the Eastern Part of Europe, with a Clinical Case Report in a Dog in Poland

Thelazia callipaeda is a zoonotic nematode transmitted by drosophilid flies. It causes ocular thelaziosis, a disease of carnivores, such as dogs, cats, and foxes, and also humans. The parasite has thus far been observed in various areas of Eurasia, including 20 countries within Europe. The present study documents its presence in the south-east region of Poland, near the Ukraine border. An adult nematode was removed from the conjunctival sac of a dog showing ocular inflammation and purulent discharge. The dog’s precise origin is unknown. Based on its localization and morphometrical features, the nematode was identified as a Thelazia callipaeda adult male. The present study is the first report of T. callipaeda in a dog in Poland.