Comparative evaluation of the prophylactic activity of a slow-release insecticide collar and a moxidectin spot-on formulation against Thelazia callipaeda infection in naturally exposed dogs in France

Thelazia callipaeda infestation in an 8-month-old male infant in Hubei, China

Thelazia callipaeda, a zoonotic nematode, primarily infests the ocular tissues of mammals, occasionally humans. Infestations in infants under 1 year of age are rarely reported. This case describes an 8‑month-old male infant diagnosed with ocular T. callipaeda infestation in Hubei, China. The infant was brought to the hospital by his mother, who reported that he had been rubbing his right eye for 3 days, accompanied by increased ocular discharge and mild tearing. Upon examination, a whitish, motile, thread-like worm was observed in the conjunctival sac of the right eye. During ophthalmological surgical exploration, a total of 10 worms were removed from the right eye, with 8 sent for identification. All 8 adult nematodes collected were morphologically identified as T. callipaeda, consisting of 4 females and 4 males. Following the removal of the nematodes, the infant's ocular symptoms rapidly resolved, with no recurrence noted during a 2-month follow-up.

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.

Feline thelaziosis (Thelazia callipaeda) in Spain: state-of-the-art and first prophylactic trial in cats

OBJECTIVES

Thelaziosis caused by the nematode Thelazia callipaeda (Spirurida, Thelaziidae) affects the eyes of domestic and wild carnivores, lagomorphs and even humans. The role of cats in spreading thelaziosis remains unclear. The present study assesses the current status of feline T callipaeda infection in Spain and presents the results of the first prophylactic trial conducted in this species.

METHODS

We retrospectively analysed the occurrence of feline thelaziosis (study 1), examined its prevalence based on cross-sectional sampling of endemic areas (study 2), and assessed the therapeutic/prophylactic benefits of a spot-on (moxidectin) and therapeutic efficacy of an eye drop (ivermectin) formulation (study 3).

RESULTS

In study 1, 69 Thelazia-infected cats were examined. Autochthonous cases were detected in 18/26 municipalities surveyed in Spain, which corresponds to 88.4% (n = 61/69) of the total number of cases. In study 2, 74 cats (20 from La Vera region and 54 from Orense province) were examined from 2011 to 2013. Ten of these cats (13.5%) were infected with T callipaeda. The infection prevalence was 40% (n = 8/20) in La Vera and 3.7% (n = 2/54) in Orense. The therapeutic efficacy of ivermectin was assessed over a summer (2011) in 12 cats, while that of moxidectin was examined over a 17-month period in seven cats. Four of these seven cats were subsequently included in an all-year-round prophylaxis trial. Treatment efficacy ranged from 91.7% (ivermectin) on day 28 after treatment to 100% (moxidectin) on day 14. Moxidectin prevented reinfections in cats.

CONCLUSIONS AND RELEVANCE

Our data confirm the endemic status of T callipaeda infection in Spain, revealing its high prevalence in cats living in known endemic areas. Moxidectin was effective in treating and preventing infection. We strongly recommend the inclusion of thelaziosis in the differential diagnosis of pets and humans presenting with ocular manifestations, along with adequate preventive measures.

Update on the treatment and prevention of ocular thelaziosis (Thelazia callipaeda) in naturally infected dogs from Spain

This study examines the therapeutic and year-round prophylactic efficacy of different formulations used in dogs in three Spanish areas where canine thelaziosis is endemic. The study was conducted as a Good Clinical Practice, multicentre, randomised field study in privately owned outdoor dogs naturally infected with Thelazia callipaeda. The active pharmaceutical ingredients tested were: an oral formulation of milbemycin oxime 12.5 mg combined with praziquantel 125 mg (A), a subcutaneous sustained-release formulation of moxidectin 10 g (B), a moxidectin 2.5% weight/volume (w/v) spot-on formulation combined with imidacloprid 10% w/v (C), and an eye drop formulation (6 µg) of ivermectin 10 mg/ml diluted 10% in propylene glycol (D). Infected dogs were randomly allocated to treatment Groups A, B, C and D. Dogs testing negative for T. callipaeda inspection in two visits (Day 7/Day 14 and D30) were enrolled in the prophylaxis trial and reallocated to the corresponding study group (A, B, C or D). Treatment efficacy ranged from 70.4% recorded in Group A 1 week after treatment, to 100% recorded in Group C on Day 30 and in Group B on Day 60. Treatment was more efficacious in Group D (85.7% 1 week after treatment) than A, but was never 100% efficacious as in Groups B and C. Year-round prophylactic efficacy was 83.3% in Group A, 100% in Group B, 93.5% in Group C and 87.5% in Group D. In conclusion, products containing moxidectin were highly efficacious both in treating and preventing canine thelaziosis. Milbemycin also emerged as a good option. However, the off-label use of topical or subcutaneous ivermectin should be avoided due to possible adverse reactions such as pruritus, irritation or redness. In endemic areas, monthly prophylaxis to limit the spread of T. callipaeda to new areas across Europe and reduce zoonotic risks is essential.

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

Cases of thelaziosis by Thelazia callipaeda have been increasing considerably in Europe throughout the 21st century, with recent emphasis on Eastern Europe. A systematic review was conducted using defined search terms across three major databases and, additionally, with the examination of the references of the 56 articles selected. Available information about epidemiological and clinical features of all cases of thelaziosis by T. callipaeda in companion animals, wildlife and humans was extracted, evaluated and subjected to qualitative and quantitative analysis. In all cross-sectional studies about dogs, cats and red foxes, males were more frequently infected than females (dogs: p = 0.0365; cats: p = 0.0164; red foxes: p = 0.0082). Adult dogs seem to be more prone to infection (p < 0.0001), as well as large-sized dogs (p < 0.0001), and companion animals that live exclusively outdoors (p < 0.0001). Dogs and red foxes involved in these cross-sectional studies harboured significantly more female than male nematodes (p < 0.0001). Thelaziosis by T. callipaeda is far from controlled in Europe. Only through updated epidemiological data, knowledge improvement and awareness can correct diagnosis and appropriate treatment and prevention be ensured to tackle this zoonosis.

Spain as a dispersion model for Thelazia callipaeda eyeworm in dogs in Europe

Thelazia callipaeda (Spirurida, Thelaziidae) causes ocular infection in carnivorous animals and humans. While growing numbers of companion dogs and sometimes cats are being diagnosed with thelaziosis, little is known about its real spread. As it has been also diagnosed in wild animals and human beings, it is considered a potential emerging zoonotic disease. This study provides information about the spread of the parasite in dogs in Spain since its initial description in 2010 until 2018. The first detection of T. callipaeda in the Principality of Andorra in 2017 is also reported. Two different studies were conducted: a) a survey in which clinical cases from veterinary practices were collected and b) a prevalence study in two endemic areas in western and central Spain (Site 1 La Vera region, Cáceres, and Site 2 El Escorial municipality, Madrid). In total, 1114 cases of thelaziosis were detected in 121 municipalities of Spain and 6 municipalities of Andorra. In 92 out these 127 municipalities, reports were of autochthonous cases. Six hundred twenty-three out of 1114 presented data collection sheet and were included in the statistical analysis: 510 cases identified by veterinarians in Spain and Andorra in Study 1, and 113 cases detected among the 234 dogs (48.3 %) examined in the prevalence study (Study 2). Prevalences were 61.3 % (84/137) for Cáceres and 29.9 % (29/97) for Madrid, being Site 1 significantly more risky (P <  0.0001, odds ratio: 3.72, CI: 2.14-4.47 %) compared to Site 2. Our study updates data for canine thelaziosis reported in the last decade in Spain and Andorra. Results highlight the urgent need for prevention strategies to control the spread of this potential zoonotic disease.

Vector-borne nematode diseases in pets and humans in the Mediterranean Basin: An update

Vector-borne diseases (VBDs) are among the leading causes of morbidity and mortality in humans and animals. The scale of VBDs is increasing worldwide, including in the Mediterranean Basin, a region exposed to climate changes. Indeed, weather conditions may influence the abundance and distribution of vectors. The vector-borne nematode diseases of dogs and cats, such as dirofilariosis, onchocercosis, thelaziosis, Cercopithifilaria, and Acanthocheilonema infections, are some of these vectorized diseases, several of which are zoonoses. They are all caused by parasitic nematodes transmitted by arthropods, including mosquitoes (Dirofilaria spp.), black flies (Onchocerca lupi), drosophilids (Thelazia callipaeda), ticks (Acanthocheilonema dracunculoides and Cercopithifilaria bainae), and fleas and lice (Acanthocheilonema reconditum). The control and prevention of these infections and diseases require a multidisciplinary approach based on strengthening collaboration between the different actors in the fields of health, research, sociology, economics, governments and citizens, to improve human, animal, and ecosystem health. This is the concept of "one health." The review aimed to provide a general update on the spatial and temporal distribution of vector-borne nematodes diseases affecting companion animals and humans, as well as the vectors involved in the Mediterranean area. Simultaneously, certain epidemiological parameters, diagnosis, treatment, and control of these diseases based on the "one health" concept will also be discussed.

Thelaziosis due to Thelazia callipaeda in Europe in the 21st century-A review

Thelazia callipaeda was first described at the beginning of the 20th century in Asia, but this eyeworm is now frequently reported in Europe in the 21st century. To date, thelaziosis has been described in the following European countries (in order of appearance): Italy, France, Germany, Switzerland, Spain, Portugal, Belgium, Bosnia and Herzegovina, Croatia, Serbia, Romania, Greece, Bulgaria, Hungary, Slovakia, the United Kingdom, Turkey and Austria. The infected vertebrate host species include domestic carnivores (dogs and cats), wild carnivores (red foxes, wolves, beech martens, wildcats and golden jackals), lagomorphs (brown hares and wild European rabbits) and humans. In Europe, 11 cases of human thelaziosis have been reported, the majority of which are autochthonous. However, some of them have been imported, a fact which highlights the importance of surveillance policies to restrict cross-border spread of the parasite. The objectives of this article are to review key aspects of the epidemiology of T. callipaeda, summarise animal and human cases in Europe and emphasise the importance of education and awareness among veterinarians, physicians (particularly ophthalmologists) and animal, in order to owners to tackle this zoonosis.

Prevention of canine ocular thelaziosis (Thelazia callipaeda) with a combination of milbemycin oxime and afoxolaner (Nexgard Spectra®) in endemic areas in France and Spain

In the past decade, canine thelaziosis due to Thelazia callipaeda has been diagnosed in an increasing number of European countries, with endemic areas being identified. A multi-center field trial was conducted in endemic areas in France and Spain to evaluate the efficacy of monthly administrations of the oral milbemycin oxime/afoxolaner combination (NexGard Spectra^®) for the prevention of T. callipaeda infection in at-risk dogs. A total of 79 dogs negative for T. callipaeda and with a clinical history of eyeworm infection in the past two years completed the study. Dogs were randomly allocated either to a negative control group (42 dogs) or to the NexGard Spectra^® treated group (37 dogs). All dogs were followed up for a 6-month period and assessed monthly for the presence of nematodes on the eyes and for the signs of ocular thelaziosis (e.g., conjunctivitis, keratitis, and ocular discharge). When the presence of nematodes was confirmed, the conjunctival fornix was flushed with a saline solution for parasite recovery and counting, and the dogs were treated appropriately. Recovered parasites were stored in 70% alcohol for subsequent morphological identification. During the course of the study, 57.1% (24/42) of the control dogs were diagnosed positive for Thelazia infection, which illustrates a high incidence rate of parasite infection. Conversely, no eyeworm was recovered from any of the 37 dogs that received NexGard Spectra^®. All parasites sampled were confirmed to be T. callipaeda. This clinical field study demonstrated that monthly administrations of NexGard Spectra^® provided 100% preventive efficacy against canine thelaziosis.

Spreading of Thelazia callipaeda in Greece

Thelazia callipaeda (Spirurida, Thelaziidae), the so-called oriental eyeworm, has been increasingly reported as an agent of infection in animals and humans from many European countries. Clinical signs range from subclinical to moderate or severe ocular disorders (e.g., epiphora, photophobia, conjunctivitis, keratitis, ulcers). The disease has been also diagnosed in animals from countries of the Balkan area (e.g., Croatia, Bosnia and Herzegovina and Serbia), but only a single case of canine thelaziosis, presumably autochthonous, was reported in Northern Greece. In this study, we provide robust information of the occurrence of thelaziosis in Greece by reporting autochthonous cases of thelaziosis in dogs (n = 46), cats (n = 3) and in one rabbit (Oryctolagus cuniculus) living in Northern and Central regions of Greece. The occurrence of a single haplotype of the cytochrome oxidase subunit 1 gene confirms that the same zoonotic haplotype of the parasite circulating in Europe is also spreading in Greece. The increased awareness of this parasitosis is crucial to limit the risk of further infections in both humans and animals in European countries.

First report of Thelazia callipaeda infection in wild European rabbits (Oryctolagus cuniculus) in Portugal

Background

Thelazia callipaeda is a zoonotic nematode that affects the eyes of domestic and wild animals, including dogs, cats and red foxes. This parasitic eye worm is transmitted by Phortica variegata, which is a zoophilic fruit fly spread in Europe. Two wild European rabbits (Oryctolagus cuniculus) found dead in north-eastern Portugal were submitted to necropsy.

Results

Both animals presented gross lesions compatible with haemorrhagic viral disease. Eye examination revealed the presence of six worms (three in each animal, on both eyes). Out of the six nematodes, five females and one male were morphologically and molecularly identified as T. callipaeda.

Conclusions

This is the first report of T. callipaeda in wild rabbits from Portugal, which reveals a new host for this parasite in southern Europe and emphasizes the importance of including thelaziosis in the differential diagnosis of ocular alterations in both animals and humans from areas where the eye worm is endemic.