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

Efficacy of a combination of esafoxolaner, eprinomectin and praziquantel (NexGard® Combo) against Thelazia callipaeda in naturally infected cats

This clinical study assessed the efficacy of a topical combination of esafoxolaner, eprinomectin and praziquantel (NexGard® Combo) in treating cats naturally infected with the eyeworm Thelazia callipaeda (Nematoda, Thelaziidae). On Study Day (SD) 0, sixteen client-owned cats with eyeworm infection were allocated to an untreated control group (G1, 8 cats) or to a NexGard® Combo treated group (G2, 8 cats) and subjected to ocular examination. Cats in G2 received the treatment as per label recommendations. On SD 7 and 14 (±1), cats were examined for the presence of eyeworms and clinical signs. On SD 14, eyeworms were collected and counted. On SD 7 and 14, all cats in G1 were still infected with eyeworms, while G2 cats were free from eyeworms on SD 7 and 14, demonstrating 100% efficacy (p < 0.0001). All collected eyeworms were morphologically and molecularly confirmed to be T. callipaeda. On SD 0, fifteen out of the sixteen cats (7 in G1 and 8 in G2) displayed inflammatory ocular signs. On SD 7, all eight untreated cats and seven treated cats displayed inflammatory ocular signs. On SD 14, five out of eight G2 treated cats had recovered, while the eight untreated cats still displayed inflammatory ocular signs. The treatment significantly reduced lacrimation and conjunctivitis (p = 0.0001). No adverse reactions occurred. This clinical study provides evidence that NexGard® Combo is highly safe and effective for the treatment of T. callipaeda infection in cats under field conditions.

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.

Laboratory Culture and Life Cycle of Thelazia callipaeda in Intermediate and Definitive Hosts

Human thelaziasis caused by Thelazia callipaeda is being increasingly reported worldwide. Notably, an epidemic trend is observed in Southwest China. Whether Phortica okadai found in Southwest China can act as a vector of T. callipaeda and human-derived T. callipaeda animal infections has not been widely reported. Here, P. okadai was maintained in a laboratory and experimentally infected with first-stage larvae collected from adult T. callipaeda that were isolated from infected human subjects. Dead P. okadai were subjected to PCR assay and dissected every two days to detect T. callipaeda. Subsequently, live flies were used to infect a rabbit. The infection procedures were performed once a day (20 min) for two weeks. The results show that L1 collected from the adult T. callipaeda could successfully parasitize P. okadai captured in Zunyi, a city in Southwest China, and developed into L3, and a rabbit was successfully infected with T. callipaeda using P. okadai as the intermediate host. The present study demonstrates a human-derived T. callipaeda infection in rabbits, through P. okadai, under laboratory conditions for the first time. These results provide insights into the transmission cycle of T. callipaeda and constitute a foundation to develop an effective treatment protocol for T. callipaeda infection.

Efficacy of fipronil/(S)-methoprene/eprinomectin/praziquantel (Broadline®) against Thelazia callipaeda in naturally infected cats

Background

The present clinical field trial was conducted to assess the efficacy of a broad-spectrum parasiticide spot-on formulation containing eprinomectin (Broadline^®) against Thelazia callipaeda eyeworm in naturally infected cats.

Methods

Fifteen privately owned cats harboring at least one live adult T. callipaeda were included in the study. Cats were randomly allocated to an untreated control group of seven cats or to a Broadline^®-treated group of eight cats. Cats were treated on Day 0; ocular examinations were performed at inclusion and on Days 7 and 14; eyeworms were recovered and counted on Day 14. The primary efficacy assessment was based on group comparison of number of T. callipaeda on Day 14.

Results

Seven days after treatment, six of eight treated cats were negative for eyeworm infection per visual examination, and on Day 14 no eyeworms were found in the treated cats while the seven untreated cats were still infected (geometric mean: 1.97). All cats had inflammatory ocular signs at inclusion; on Day 14, five of eight treated cats had recovered while all untreated control cats were still symptomatic. All collected parasites were confirmed to be T. callipaeda by morphology and molecular characterization.

Conclusions

A single treatment with Broadline^® provided 100% efficacy against feline thelaziosis and improved related ocular inflammation signs.

Graphical abstract

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.

Zoonotic Thelazia californiensis in dogs from New Mexico, USA, and a review of North American cases in animals and humans

Thelazia californiensis is a spirurid nematode found in the conjunctival sac of domestic and wild animals, including humans, across the western United States of America. Herein, we report two cases of thelaziosis by T. californiensis in dogs from New Mexico, United States, based on integrated morphological and molecular approaches. Nematode specimens collected from the conjunctiva of both dogs were identified as T. californiensis based on morphology. Our study substantially expands the knowledge on morphometry of this nematode species. Therefore, these data will be useful for accurate diagnosis of thelaziosis in domestic animals, wildlife and humans in North America, using classical, microscopy-based methods. We characterized for the first time the mitochondrial cytochrome c-oxidase subunit 1 (COI) and 12S genes of T. californiensis. While these markers support the validity of T. californiensis, they were not very informative for elucidating the phylogenetic relationships among Thelazia species. Nevertheless, the characterization of these diagnostic markers for T. californiensis will be useful for studies on the epidemiology, molecular xenomonitoring of fanniid vectors, and population genetics of this multi-host, zoonotic parasite.

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.

Antiparasitics in Animal Health: Quo Vadis?

Antiparasitics acting on endo- or ectoparasites represent the second largest segment of the global animal health market, accounting for 23% of market share. However, relatively few novel antiparasitic agents have been introduced into the market during recent decades. One exception, and a groundbreaking 21st century success story, are the isoxazolines, whose full potential has not yet been entirely explored. Unfortunately, resistance issues are present across most parasitic diseases, which generates a clear market need for novel resistance-breaking antiparasitics with new modes/mechanisms of action. Recent advances in science and technologies strongly suggest that the time is right to invest in new modalities such as parasitic vaccines or in environmentally friendly interventions.

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.

Ophthalmic Thelazia callipaeda infections: first feline and new canine imported cases in Germany

The first case of feline ocular Thelazia callipaeda infection and two new canine imported infections in West Germany are here described. The three animals had a history of recent travel to/from other countries. The young adult cat imported from Spain presented an intermittent unilateral ocular discharge. During in-depth ophthalmic examination, a single alive nematode was removed from the conjunctival compartment of the affected eye. Referring to the canine cases, an adult female dog originated from Kenya presented epiphora and mucous whitish-grey discharge of the right eye. During flushing of the nasolacrimal duct two small, thin and long nematodes were removed. Furthermore, a male Borzoi racing dog with regular visit to racing tracks in different countries presented ocular mucous discharge. At ophthalmologic examination, two transparent-whitish vital nematodes were removed. All nematode specimens of the three cases were morphologically identified as adult T. callipaeda parasites. The animals were treated orally with milbemycin oxime (2.0 mg/kg; cat) or milbemycin oxime/praziquantel (0.5 mg/kg and 5.0 mg/kg; dogs) twice with 1-week interval resulting in complete resolution of symptoms. The repeated introduction of patent T. callipaeda-infected animals, especially from southern and eastern endemic countries, will ease the establishment of ophthalmic thelaziosis in Northern Europe. The male fruit fly, Phortica variegata, an intermediate host of T. callipaeda, is endemic within European countries. Considering the clinical and zoonotic relevance of ophthalmic thelaziosis, enhanced disease awareness of European medical and veterinarian doctors and in-depth eye examination for proper detection of T. callipaeda are crucial for appropriate anthelmintic treatments and to limit spreading of the infection.

Canine thelaziosis in the Czech Republic: the northernmost autochthonous occurrence of the eye nematode Thelazia callipaeda Railliet et Henry, 1910 in Europe

The eye nematode Thelazia callipaeda Railliet et Henry, 1910 (Spirurida: Thelaziidae) is a vector-borne zoonotic nematode infecting a range of wild and domestic carnivores as well as humans. It is considered to be a causative agent of emerging and neglected disease and currently invades central part of Europe. Nematodes were collected from the eye of a dog living in Prague, which never travelled outside the Czech Republic. The nematodes were identified based on their morphology and partial sequence of the cox1 gene as T. callipaeda haplotype 1. This finding represents the northernmost record of autochthonous canine thelaziosis in Europe. The insufficient control of imported animals as well as free movement of dogs and wild carnivores within Europe probably facilitates spreading of T. callipaeda throughout the continent. To better understand the spreading of T. callipaeda and to prevent its zoonotic transmissions, information about the risk of this infection in newly invaded countries should be disseminated not only among veterinarians and physicians, but also within the community of pet owners and hunters.

Molecular characterisation of acanthocephalans from Australian marine teleosts: proposal of a new family, synonymy of another and transfer of taxa between orders

We provide molecular data (cox1, 18S rDNA and 28S rDNA) for 17 acanthocephalan species and 20 host-parasite combinations from Australian marine teleosts collected from off Queensland, Australia. Fourteen of these acanthocephalans are characterised with molecular data for the first time and we provide the first molecular data for a species of each of the genera Heterosentis Van Cleave, 1931, Pyriproboscis Amin, Abdullah & Mhaisen, 2003 and Sclerocollum Schmidt & Paperna, 1978. Using 18S and 28S rDNA sequences, the phylogenetic position of each newly sequenced species is assessed with both single-gene and concatenated 18S+28S maximum likelihood and Bayesian inference analyses. Additional phylogenetic analyses focusing on the genus Rhadinorhynchus Lühe, 1912 and related lineages are included. Our phylogenetic results are broadly consistent with previous analyses, recovering previously identified inconsistencies but also providing new insights and necessitating taxonomic action. We do not find sufficient evidence to recognise the Gymnorhadinorhynchidae Braicovich, Lanfranchi, Farber, Marvaldi, Luque & Timi, 2014 as distinct from the Rhadinorhynchidae Lühe, 1912. The family Gymnorhadinorhynchidae and its sole genus, Gymnorhadinorhynchus Braicovich, Lanfranchi, Farber, Marvaldi, Luque & Timi, 2014, are here recognised as junior synonyms of Rhadinorhynchidae and Rhadinorhynchus, respectively. The two species currently assigned to Gymnorhadinorhynchus are recombined as Rhadinorhynchus decapteri (Braicovich, Lanfranchi, Farber, Marvaldi, Luque & Timi, 2014) n. comb. and Rhadinorhynchus mariserpentis (Steinauer, Garcia-Vedrenne, Weinstein & Kuris, 2019) n. comb. In all of our analyses, Rhadinorhynchus biformis Smales, 2014 is found basal to the Rhadinorhynchidae + Transvenidae Pichelin & Cribb, 2001, thus resulting in a paraphyletic Rhadinorhynchidae. It appears that R. biformis may require a new genus and family; however, morphological data for this species are currently insufficient to adequately distinguish it from related lineages, thus we defer the proposal of any new higher-rank names for this species. Species of the genus Sclerocollum, currently assigned to the Cavisomidae Meyer, 1932, are found nested within the family Transvenidae. We transfer the genus Sclerocollum to the Transvenidae and amend the diagnosis of the family accordingly. The genera Gorgorhynchoides Cable & Linderoth, 1963 and Serrasentis Van Cleave, 1923, currently assigned to the Rhadinorhynchidae, are supported as sister taxa and form a clade in the Polymorphida. We transfer these genera and Golvanorhynchus Noronha, Fabio & Pinto, 1978 to an emended concept of the Isthomosacanthidae Smales, 2012 and transfer this family to the Polymorphida. Lastly, Pyriproboscis heronensis (Pichelin, 1997) Amin, Abdullah & Mhaisen, 2003, currently assigned to the Pomphorhynchidae Yamaguti, 1939, falls under the Polymorphida in our analyses with some support for a sister relationship with the Centrorhynchidae Van Cleave, 1916. As this species clearly does not belong in the Pomphorhynchidae and is morphologically and molecularly distinct from the lineages of the Polymorphida, we propose the Pyriprobosicidae n. fam. to accommodate it.

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.

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.

The first autochthonous case of feline ocular thelaziosis in Austria

Over the last 30 years, Thelazia callipaeda (Spirurida: Thelaziidae) has increasingly been reported as an agent of ocular infections in animals and humans throughout Europe. Following the cases of canine ocular thelaziosis recently recorded in Austria for the first time, in the present paper, we describe the first case of T. callipaeda infection in an Austrian cat with no history of traveling abroad. This finding further supports the occurrence of the parasite’s autochthonous transmission cycle in the country. The cat showed serous ocular discharge, conjunctival hyperemia, and mild conjunctival edema in the right eye. Mechanical removal of the parasite from the cat’s eye, in combination with milbemycin oxime/praziquantel oral treatment and topical use of tobramycin/dexamethasone eye drops led to complete resolution of the clinical signs within 2 weeks. Results presented in the current study are of great importance for the local veterinarians who seemed largely unaware of this zoonotic parasite. Therefore, increased awareness of medical and veterinary communities is imperative for preventing further infections in both animals and humans.