Case Report: Conjunctival Infestation with Thelazia gulosa: A Novel Agent of Human Thelaziasis in the United States

Diversity of Thelazia spp. in domestic cattle from Romania: epidemiology and molecular diagnosis by a novel multiplex PCR

BACKGROUND

Thelaziosis is a neglected vector-borne disease caused by parasitic nematode worms of the genus Thelazia which affects various hosts. Limited attention has been given to ungulate-associated Thelazia species. Current diagnosis of thelaziosis and the identification/differentiation of species heavily relies on morphological features. Therefore, we conducted an epidemiological study in Romanian cattle, with the aim to obtain morphological and molecular data that can be used for species identification.

METHODS

The eyes of 705 slaughtered cattle were sampled and subjected to morphological identification, morphometric analysis, and molecular characterization. PCR amplification and sequence analysis were performed based on the cytochromec oxidase subunit 1 (COI) gene. Statistical tests assessed the correlations between infection parameters and ecological or biogeographical factors. A novel PCR method was developed based on the consensus sequence from each species. Specific forward primers were designed for each of the three species, and a reverse primer (COIintR) was used for all reactions. A consensus thermal profile was established by gradient PCR amplification of each species separately.

RESULTS

Of the sampled cattle, 19.3% were infected with Thelazia spp. Prevalence varied significantly with ecogeographical factors. A total of 585 Thelazia nematodes were recovered, with T. rhodesi being the most abundant, followed by T. skrjabini and T. gulosa. Morphometric and molecular analyses supported the morphological identification, yielding unique sequences for each species. From the 59 T. rhodesi specimens sequenced, 29 unique sequences were obtained, with a 99.1-99.85% nucleotide identity to the only other COI sequence present in GenBank®. All nine T. gulosa isolates were unique (99.37-100% nucleotide identity to other sequences), while T. skrjabini specimens displayed 98.47-100% nucleotide identity to the sole available sequence.

CONCLUSIONS

Bovine thelaziosis is prevalent in Romania, raising concerns for animal welfare and potential economic impacts. Infected cattle grazing alongside vulnerable wild ruminants, such as the European bison, may affect conservation efforts. Our newly developed multiplex PCR shows promise as a valuable surveillance tool, enabling the detection of occult infections in apparently healthy animals through lachrymal secretion testing.

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.

Rare Thelazia californiensis infant ocular infestation

Purpose

A rare case of Thelazia californiensis ocular infestation was diagnosed and treated in an 11-month-old patient.

Observations

The patient presented with a visual acuity of 20/130 OU by Teller cards. Exam demonstrated a white, mobile worm in the inferomedial fornix of the right eye. The remainder of the exam was otherwise normal. The worm was removed under anesthesia and identified as Thelazia californiensis by the Division of Parasitic Diseases and Malaria, at the Centers for Disease Control and Prevention.

Conclusions and importance

This case demonstrates a rare but important cause of follicular conjunctivitis and mobile foreign bodies, especially in patients with a supportive history of exposure to the intermediate and definitive hosts of Thelazia species.

Recent trends in the use of social media in parasitology and the application of alternative metrics

In recent times, the use of social media for the dissemination of “news and views” in parasitology has increased in popularity. News, Twitter and Blogs have emerged as commonplace vehicles in the knowledge dissemination and transfer process. Alternative metrics (“altmetrics”), based on social media mentions have been proposed as a measure of societal impact, although firm evidence for this relationship is yet to be found. Nevertheless, increasing amounts of data on “altmetrics” are being analysed to identify the nature of the unknown impact that social media is generating. Here, we examine the recent, and increasing use of social media in the field of parasitology and the relationship of “altmetrics” with more traditional bibliometric indicators, such as article citations and journal metrics. The analyses document the rise and dominance of Twitter as the main form of social media occurring in the discipline of parasitology and note the contribution to this trend of Twitter bots that automatically tweet about publications. We also report on the use of the social referencing platform Mendeley and its correlation to article citations; Mendeley reader numbers are now considered to provide firm evidence on the early impact of research. Finally, we consider the Twitter profile of 31 journals publishing parasitology research articles (by volume of papers published); we show that 13 journals are associated with prolific Twitter activity about parasitology. We hope this study will stimulate not only the continued and responsible use of social media to disseminate knowledge about parasitology for the greater good, but also encourage others to further investigate the impact and benefits that altmetrics may bring to this discipline.

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We highlight and document the rise of social media and its use in parasitology.

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Twitter activity within the parasitology community has increased significantly over the last 10 years.

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Mendeley reader activity is strongly correlated with an article's citations.

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Thirteen journals are associated with prolific Twitter activity about parasitology.

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A Journalʼs social media strategy is important to authors.

Rabbit-derived human Thelazia callipaeda infection: a case report

In November 2021, a 19-year-old medical student was diagnosed with a rabbit-derived Thelazia callipaeda infection in her left eye. She visited her doctor because she removed the white object by herself with a cotton swab 2 days earlier. She explained to the doctor that she rubbed her eyes without washing her hands when rabbit hair got into her eyes during the animal experiment class at school 2 weeks earlier. The other 2 worms were then taken out with ophthalmic forceps and were placed into physiological saline. The worms were sent to the Shandong Academy of Eye Disease Prevention and Therapy for examination. After identification, the worms were regarded as the female T. callipaeda. Ofloxacin eye drops and peranapulin eye drops were administered to control inflammation. No abnormality was found in the follow-up 2 weeks and 1 month later. This report highlights that it is very important to strengthen the health and safety education of medical students during animal experiment classes.

An annotated checklist of the eukaryotic parasites of humans, exclusive of fungi and algae

The classification of "parasites" in the medical field is a challenging notion, a group which historically has included all eukaryotes exclusive of fungi that invade and derive resources from the human host. Since antiquity, humans have been identifying and documenting parasitic infections, and this collective catalog of parasitic agents has expanded considerably with technology. As our understanding of species boundaries and the use of molecular tools has evolved, so has our concept of the taxonomy of human parasites. Consequently, new species have been recognized while others have been relegated to synonyms. On the other hand, the decline of expertise in classical parasitology and limited curricula have led to a loss of awareness of many rarely encountered species. Here, we provide a comprehensive checklist of all reported eukaryotic organisms (excluding fungi and allied taxa) parasitizing humans resulting in 274 genus-group taxa and 848 species-group taxa. For each species, or genus where indicated, a concise summary of geographic distribution, natural hosts, route of transmission and site within human host, and vectored pathogens are presented. Ubiquitous, human-adapted species as well as very rare, incidental zoonotic organisms are discussed in this annotated checklist. We also provide a list of 79 excluded genera and species that have been previously reported as human parasites but are not believed to be true human parasites or represent misidentifications or taxonomic changes.

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.

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.

A Second Case of Human Conjunctival Infestation With Thelazia gulosa and a Review of T. gulosa in North America

We describe a second case of human infection caused by Thelazia gulosa (the cattle eye worm), likely acquired in California. For epidemiologic purposes, it is important to identify all Thelazia recovered from humans in North America to the species level.

The Nematodes Thelazia gulosa Railiet and Henry, 1910 and Thelazia skrjabini Erschov, 1928 as a Cause of Blindness in European Bison (Bison bonasus) in Poland

PURPOSE

The nematodes of the genus Thelazia are the cause of eye diseases of wild and domestic ruminants throughout the world. The aim of the study was to describe clinical cases of thelasiosis in European bison (Bison bonasus) in Poland, and provide morphometrical features of Thelazia gulosa Railiet and Henry, 1910 and Thelazia skrjabini Erschov, 1928 regarded as potentially useful for species differentiation METHODS: The conjunctival sacs, tear ducts, the surface of the cornea and nicitating membrane collected from bison were rinsed with saline solution. Any nematodes isolated from the sediment were subjected to morphometric analysis.

RESULTS

Thirteen of the 16 examined European bison were infected with Thelazia nematodes, belonging to the species T. gulosa and T. skrjabini. The intensity of infection ranged from one to six (mean intensity 5), and four to 29 (mean intensity 14) nematodes T. skrjabini and T. gulosa respectively. Congestion of conjunctival sac, keratitis and corneal opacity, corneal ulceration and perforation as well as purulent eyeball inflammation were observed in infected animals.

CONCLUSIONS

Thelazia gulosa and T. skrjabini can be identified by morphometrical features. As thelasiosis might be a serious threat for protected population of European bison, further studies are needed of the epidemiology and pathology of this emerging parasitosis in Poland.

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.

A Case of Human Thelaziasis and Review of Chinese Cases

PURPOSE

Human cases of thelaziasis caused by Thelazia callipaeda have increased in China in recent years. Although this species is of medical importance, our knowledge about the epidemiology of thelaziasis is still fragmentary. This study first reports a case of thelaziasis in central China. Then, the epidemiology of thelaziasis in China in the past 100 years (1917-2018) is reviewed.

METHODS

A 5-year-old girl experienced discomfort in her left eye. Four thread-like worms were seen in the nasal upper eyelid of the left eye. The symptoms disappeared after these parasites were removed. In addition, we reviewed studies of Chinese human thelaziasis cited in articles or book chapters in all languages from inception to 31 Dec 2019.

RESULTS

China is the nation with the most reports of thelaziasis (653 cases) in the world. More human cases were reported in central and eastern China than in other areas, and the majority of cases were from rural areas in poor socioeconomic settings.

CONCLUSION

Special attention should be paid to this neglected disease in China. The use of a One Health approach is imperative for preventing eyeworm infections in humans.

A human corneal ulcer caused by Thelazia callipaeda in Southwest China: case report

In this study, we describe a rare human case with corneal ulcer caused by thelaziosis in a 69-year-old man in Southwest China. A male nematode was discovered and removed from the patient's right eye with a long spicule and further identified by sequencing mitochondrial cox1 gene. The ophthalmologic and molecular biological evidence demonstrates the corneal ulcer caused by T. callipaeda infection, which is mainly distributed in Asian and European countries. Most T. callipaeda infections are emerged in the conjunctiva, leading to conjunctivitis. To the best knowledge of the authors, corneal ulcers caused by T. callipaeda have not been reported yet.

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.

Human ocular thelaziasis caused by gravid Thelazia callipaeda - A unique and rare case report

An 80-year-old male reported to the clinic with complaints of diminished vision, foreign body sensation, and occasionally some black object moving in front of the right eye. Detailed ocular examination revealed three slender creamy white live worms in the conjunctival sac of the right eye. Total three worms were retrieved and sent to the pathology department for detailed examination. The worm was identified as gravid Thelazia callipaeda. As per the search results in PubMed and Cochrane search engine, this is the first report of human case of gravid Thelazia infestation with simultaneous existence of embryonated or ensheathed eggs and primary-stage larvae in the same worm.

The Discovery of Helminth Life Cycles

The origin of worms, which were occasionally excreted by some individuals, has left humans wondering for centuries. The story of the gradual discovery of the life cycles of the parasitic helminths is a fascinating one, peppered with misconceptions, misguided by dogmas of the church and enlightened by brave men, who did not recant when they were attacked by the opinion leaders of their time. This article will try to pinpoint some of the key discoveries which turned out to be milestones for the elucidation of the secret life of helminths.

Medical Parasitology Taxonomy Update, 2016-2017

Parasite taxonomy continues to change as molecular and morphologic studies enhance our understanding of parasite relatedness. This minireview builds on the information provided in the last taxonomy update in this journal to summarize new and revised clinically relevant human parasite taxonomic changes that have occurred in 2016 and 2017.

A Systematic Overview of Zoonotic Helminth Infections in North America

Zoonotic helminths are frequent human parasites that generally complete their natural life cycle in the absence of humans. This review encompasses 30 common or clinically relevant zoonotic helminth infections that are endemic to North America. For each organism or disease, the following information is briefly reviewed: taxonomy, biology, and life cycle, epidemiology, route of transmission for the human host, clinical manifestations, pathologic features, treatment, and laboratory diagnosis. Illustrations are provided for select parasites.

Human Thelaziasis: Emerging Ocular Pathogen in Nepal

Thelaziasis is an ocular arthropod-borne, zoonotic disease of the eye infecting the conjunctival sac, lacrimal duct, and lacrimal gland caused by a nematode of the genus Thelazia. We report the first case of human ocular thelaziasis in Nepal in a 6-month-old child from a Rukum district, Nepal. The infant presented with conjunctivitis, and his visual acuity and dilated fundal examination were normal. A total of 6 worms were removed for identification. Collected nematodes were identified based on morphological keys as Thelazia callipaeda. The patient’s symptoms improved after removal of the nematodes.