Thelazia Species Research Articles

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

BackgroundThelaziosis 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.MethodsThe 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.ResultsOf 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.ConclusionsBovine 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.Graphical

Human Ocular Thelaziasis: A Case Report

Thelaziasis is a zoonotic disease which affects the eye of domestic and wild carnivores caused by the nematode Thelazia. It is transmitted to humans by secretophagous arthropod-borne zoophilic nonbiting flies of the family Drosophilidae. Human thelaziasis is rare and occurs in poor socio-economic families of the rural locations where people live in close proximity with animals. A one and halfyear-old was presented to the outpatient ophthalmology clinic after her mother noticed a whitish, thread-like worm in her right eye. A total of four worms were mechanically removed from her right eye. All the collected worms were gravid female nematodes of Thelazia species. The present case of human ocular thelaziasis from Palpa, Nepal is presented for its rarity.

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.

Wriggly creatures coming out of eye: case report on human ocular thelaziasis

Ocular Thelaziasis is an arthropod-borne, zoonotic disease of the eye affecting the conjunctival sac,lacrimal duct, and lacrimal gland caused by a nematode of the genus Thelazia. Thelazia species aretransmitted by different species of Muscidae, which are a family of flies with worldwide distribution.The present study reports a case of human ocular Thelaziasis in a 13-year-old female patient.Species Thelazia callipaeda was confirmed based on microbiological examination. The patient wastreated with anti-helminthic drugs and was relieved of the symptoms without recurrence.

A REPORT OF THREE CASES OF HUMAN OCULAR THELAZIASIS IN MANIPUR MICROBIOLOGY

BACKGROUND: This is a report of 3(three) cases of human ocular thelaziasis caused by Thelazia species. CASE CHARACTERISTIC: Three patients aged 34 year, 27 years and 5 years old male attended Department of ophthalmology, RIMS, Imphal during the period from 2017 to 2019 with chief complaint of increased lacrimation, itching and irritation. The parasites were surgically removed from the eyes of patients in one piece under local anaesthesia and brought to Microbiology department and were processed for identification. They were all suffering from ocular Thelaziasis. RESULTS: These worms were intact, slender, thread-like and creamy white in colour. On the basis of recovery site, gross appearance and microscopical findings, the worms were identified to be Thelazia species. CONCLUSION: This case report highlights the importance of “thelaziasis” and emphasize on further study of the morbid conditions and sequelae caused by the worm is required to minimise human infection.

Therapeutic Efficacy of Ivermectin against Thelaziasis in Cattle

Background: Thelazia species are arthropod-borne nemathelminths causing thelaziasis of eyes in various domestic animals and humans. The adult and larval stages of Thelazia spp. are responsible for eye disease. The treatment of ocular thelaziasis includes topical or parenteral introduction of 1% moxidectin, 10% imidacloprid along with levamisole and ivermectin in the infected animal. Methods: Sixty-two cattle were randomly divided into two groups of 31 each. The group I was administered with ivermectin at 200 mcg/kg body weight subcutaneously whereas group II was subjected to mechanically removal of worms from the eyes Result: The treatment with ivermectin showed high therapeutic efficacy of up to 87.1% as compared to 16.67% in mechanical removal of worms.

Parasites of mithun (Bos frontalis) in North Eastern hilly region of India-A review

Parasitism is a common problem for mithun (Bos frontalis) resulting in production losses in terms of meat and milk. Prevalence of ectoparasites infestation including Rhipicephalus microplus, Ambylomma testuidinarium, Ixodes ovatus and I. acutitarsus, has been reported based on taxonomic studies and PCR amplification of conserved gene. Different gastrointestinal helminth like Haemonchus contortus, Mecistocirrus digitatus, Trichostrongylus spp., Oesophagostomum spp., Trichuris spp s, Thelazia species, Strongyloides papillosus, different amphistomes and Fasciola gigantica were also reported from mithun from India. Among filarial worms, Setaria digitata was recorded from peritoneal cavity of mithun and its molecular confirmation was done based on PCR amplification of marker genes. Tapeworm infestation viz. Moniezia expansa, M. benedeni, hydatid cyst and Cysticercus tenuicollis, were also commonly occurred in mithun. Enteric protozoa like different species of Eimeria, Cryptospordium species, Balantidium coli, has been diagnosed based on morphological identification sporulated oocysts and developmental stages found on faecal examination. Another obligate intracellular parasites Toxoplasma gondii, was also diagnosed based on ELISA and modified agglutination test. An integrated approach incorporating deworming, good livestock management and optimum feeding management practice coupled with vaccination programme will make successful parasite control programme in near future.

Morphological and Mitochondrial Genomic Characterization of Eyeworms (Thelazia callipaeda) from Clinical Cases in Central China.

Thelazia callipaeda, also called the oriental eyeworm, is the major etiological agent of human thelaziasis. Cases of thelaziasis have increased in recent years in China. Although this species is of medical importance, the genetics and phylogenetic systematics of T. callipaeda are poorly understood. In this study, we first reported three cases of thelaziasis in central China. All clinical isolates were identified as T. callipaeda according to morphological characteristics by light microscopy and scanning electron microscopy. Next, complete mitochondrial (mt) genomes for the three T. callipaeda isolates from different geographical locations were fully characterized using an Illumina sequencing platform. In addition, all available mt genomes of spirurid nematodes in GenBank were included to reconstruct the phylogeny and to explore the evolutionary histories of the isolates. The genome features of the T. callipaeda isolates contained 12 PCGs, 22 transfer RNA genes, two ribosomal RNA genes and a major non-coding region. The mtDNA nucleotide sequences of the T. callipaeda isolates from different hosts and different locations were similar. The nad6 gene showed high sequence variability among all isolates, which is worth considering for future population genetic studies of T. callipaeda. Phylogenetic analyses based on maximum parsimony and Bayesian inference methods revealed close relationships among Thelaziidae, Onchocercidae, Setariidae, Gongylonematidae, Physalopteridae, Dracunculidae, and Philometridae. The monophyly of the T. callipaeda isolates from different hosts and distinct geographical locations was confirmed. The entire mt genomes of T. callipaeda presented in this study will serve as a useful dataset for studying the population genetics and phylogenetic relationships of Thelazia species.

A case of ocular thelaziasis in a 2.5 years old Holstein heifer

A 2.5-years-old, Holstein lactating dairy cow was presented to the Veterinary Health Center with severe conjunctivitis and exuberant granulation tissue formation of the left eye. Upon close examination of the eye, a 2-cm long slender-shaped nematode was found in the conjunctival sac. The nematode was examined by a veterinary parasitologist and determined to be Thelazia species. The exuberant granulation tissue was surgically removed and a total of 0.5 mL of 1% levamisole was injected subconjunctivally. Levamesole was also injected subcutaneously at a dose of 10 mg/kg of body weight and repeated after 15 days. The cow made a complete recovery within 25 days following treatment. This is the first case report of ocular thelaziasis in dairy cattle in Jordan.

Mitochondrial Genome of the Eyeworm, Thelazia callipaeda (Nematoda: Spirurida), as the First Representative from the Family Thelaziidae

Human thelaziosis is an underestimated parasitic disease caused by Thelazia species (Spirurida: Thelaziidae). The oriental eyeworm, Thelazia callipaeda, infects a range of mammalian definitive hosts, including canids, felids and humans. Although this zoonotic parasite is of socio-economic significance in Asian countries, its genetics, epidemiology and biology are poorly understood. Mitochondrial (mt) DNA is known to provide useful genetic markers to underpin fundamental investigations, but no mt genome had been characterized for any members of the family Thelaziidae. In the present study, we sequenced and characterized the mt genome of T. callipaeda. This AT-rich (74.6%) mt genome (13,668 bp) is circular and contains 12 protein-coding genes, 22 transfer RNA genes and two ribosomal RNA genes, but lacks an atp8 gene. All protein-coding genes are transcribed in the same direction; the gene order is the same as those of Dirofilaria immitis and Setaria digitata (Onchocercidae), but distinct from Dracunculus medinensis (Dracunculidae) and Heliconema longissimum (Physalopteridae). Phylogenetic analyses of the concatenated amino acid sequence data for all 12 protein-coding genes by Bayesian inference (BI) showed that T. callipaeda (Thelaziidae) is related to the family Onchocercidae. This is the first mt genome of any member of the family Thelaziidae and should represent a new source of genetic markers for studying the epidemiology, ecology, population genetics and systematics of this parasite of humans and other mammals.

Ocular thelaziasis in Assam: A report of two cases

Small, white, thread-like, motile worms were recovered from the conjunctival sac of a 13-year-old girl and a 50-year-old woman from Dibrugarh district, Assam, India. They were identified as thelazia species. These two cases have been reported due to their rarity in India and elsewhere.

Morphological differentiation among three Thelazia species (Nematoda: Thelaziidae) by scanning electron microscopy

Thelaziasis is an ocular infection of several mammals caused by nematodes of the genus Thelazia (Spirurida, Thelaziidae). The adults live in the lachrymal ducts and conjunctival sacs of infected animals, and transmission occurs by means of different species of muscids. T. rhodesi, T. skrjabini, and T. gulosa affect mainly cattle, inducing conjunctivitis, keratitis, and ocular discharge. This article describes the morphological features of adult T. rhodesi, T. skrjabini, and T. gulosa by scanning electron microscopy and highlights the most relevant differences for their identification.

Ocular complications of barren brome exposure in a suckler herd

THE presence of a foreign body trapped between the palpebral conjunctiva and the cornea, in folds of palpebral conjunctiva, or above or below the nictitating membrane is an infrequent cause of ocular disease in cattle. Rebuhn (1995) suggested that plant material is the most common cause found in animals transported in open trailers or kept in windy areas, leading to epiphora, blepharospasm, conjunctival hyperaemia, chemosis and eventually corneal ulceration. Single cases involving plant material (Schecter and others 1985) and the presence of Thelazia species parasites in many animals have been reported in the UK (Arbuckle and Khalil 1976, 1978). This short communication describes an outbreak of conjunctival foreign bodies in a suckler herd caused by the seed of the herbaceous weed barren brome (Anisantha sterilis) also called sterile brome, drake or haver-grass (Fig 1), present in large-bale haylage. The affected farm was an organic mixed beef, sheep, arable and poultry enterprise in Somerset. The beef herd comprised 49, mainly pedigree, south Devon spring-calving suckler cows, two bulls and 78 youngstock of various ages. Winter feeding was predominantly grass silage, but some hay and haylage was also fed. Starting in late January 2005, haylage was fed off the floor behind a feed barrier to all stock. In early February, several of the cows and youngstock were noted to have ocular discharge and signs of discomfort. Of these animals, 10 were separated and submitted for veterinary examination. Presenting clinical signs included blepharospasm, epiphora, chemosis and conjunctival hyperaemia. Foreign bodies consisting of barren brome florets (reproductive units composed of a small flower/seed encased in longer fibrous sheath [Hubbard 1968] Fig 1b) were discovered embedded in the conjunctiva at various sites around the eye (Fig 2). Varying degrees of corneal ulceration were present in most cases. Foreign bodies were removed under topical local anaesthesia (amethocaine hydrochloride 1 per cent; Minims Amethocaine; Chauvin) using fine artery forceps, and oxytetracycline (Engemycin 5 per cent; Intervet) was administered subconjunctivally. The source of the problem was immediately identified by the herd owner, who was aware that barren brome was present in the haylage. Discarding the substantial quantity remaining was not considered commercially viable, and therefore presenting the haylage further back from the feed barrier (to prevent cattle burying their heads in the forage) was implemented immediately. Four days after the initial visit, further veterinary attention was requested. The whole herd was examined; a total of 19 animals was identified with signs of keratoconjunctivitis (17 unilaterally and two bilaterally). In 13 of these, florets were identified and removed, commonly from the lateral or medial canthi or under the nictitating membrane. In many affected eyes, multiple florets were present, and in one eye, four florets were found at various locations. Three animals also had signs of reflex anterior uveitis (episcleral congestion and miosis); these were treated with systemic meloxicam (Metacam; Boehringer Ingelheim). The incidence of disease in adult animals appeared substantially lower than in youngstock. Consequently, advice was given to feed the remaining haylage only to adults. Discarding the remainder of the haylage was still not considered practical. A third visit was made to re-examine the whole herd three days later. A total of 14 animals required treatment, of which three were repeat cases. Over the following six weeks, six cases were treated in the course of four visits. Resolution was uneventful in all cases. The case details are summarised in Table 1. The control of weeds on organic pasture has been a problem since the emergence of the organic movement (Bond and Grundy 2001). Control of barren brome relies predominantly on cutting fields before the brome goes to seed (Bond and Turner 2005). Other control measures include deep cultivation (Froud-Williams and others 1984) and reseeding. In this case, barren brome had previously been seen in arable crops and on pasture on the farm; however, because the farm was organic, there was no way of removing the brome from the fields during that season because the use of herbicides was restricted. Where barren brome had been present in previous years, the fields were mown early before the brome had seeded. Unfortunately, a period of wet weather just before the fields were due to be cut in 2004 meant that grass was cut much later than originally planned. As a result large numbers of barren brome seed heads were included in the haylage. The outbreak of conjunctival foreign bodies that occurred as a consequence lasted a number of weeks and had significant costs in terms of veterinary fees, stockman time, drug costs and possibly reduced weight gains. Unfortunately, discarding the haylage and purchasing additional organic forage was not considered economically or practically viable. Veterinary Record (2006) 159, 388-389

Parasitologic Examination of the Eyes, Esophagus, Lungs, Rumen, and Feces of Cattle and of the Small Intestine of Horses at Necropsy in Central Kentucky, U.S.A., in 2000 and 2001

A parasitologic survey for internal parasites was done at routine necropsy of cattle (N = 142) and horses (N = 190, including 1 donkey) at the Livestock Disease Diagnostic Center, University of Kentucky, in 2000 and 2001. The eyes, esophagus, lungs, rumen, and feces were examined from the cattle, and the small intestine was scrutinized from the horses. Endoparasites recovered from the cattle (percent infected) were Thelazia skrjabini (13%) and Thelazia gulosa (8%) from the eyes. One or both Thelazia species were recovered from 16% of the cattle, and Gongylonema pulchrum (2%) was recovered from the esophagus. The types of eggs present in the feces of cattle (percent positive) were Haemonchus–Ostertagia–Trichostrongylus (53%), Nematodirus (13%), Strongyloides (3%), Trichuris (3%), Capillaria (1%), and Moniezia (4%). Lungworm (Dictyocaulus viviparus) larvae were not detected in cattle feces. No parasite was found in the lungs or rumen of necropsied cattle. Parasites found in the small intestine of the horses (percent infected) were Gasterophilus intestinalis, third instar (3%), Gasterophilus nasalis, third instar (3%), Parascaris equorum, immature (5%), Parascaris equorum, mature (7%), Anoplocephala perfoliata (15%), and Anoplocephala magna (0.05%).

Differentiation among three species of bovine Thelazia (Nematoda: Thelaziidae) by polymerase chain reaction–restriction fragment length polymorphism of the first internal transcribed spacer ITS-1 (rDNA)

Thelazia gulosa, Thelazia rhodesi and Thelazia skrjabini are nematodes transmitted by some species of Musca (Diptera: Muscidae) which cause ocular infestations in bovines. Differences in the rDNA of these species were determined by a PCR using different sets of relatively conserved oligonucleotide primers. PCR on the first internal transcribed spacer (ITS-1) revealed differences in size in Thelazia species (437 bp for T. gulosa, 370 bp for T. rhodesi and 506 bp for T. skrjabini) while the DNA control of Musca spp. was not amplified. The ITS-1 amplicons of the three species were sequenced and then analysed. The GC contents ranged from 26 to 36% and the level of differences in the nucleotide sequences of ITS-1 was lower between T. skrjabini and T. gulosa (39%) than the latter and T. rhodesi (49–56%). Restriction fragment length polymorphism (RFLP) of ITS-1 amplicons was also carried out and the restriction profiles compared. Clear genetic differences among the three Thelazia examined were demonstrated by using the enzymes HpaII, CpoI and SspI. This PCR–RFLP for the delineation of T. gulosa, T. rhodesi and T. skrjabini offers prospects as a molecular epidemiological tool to study parasite transmission patterns and prevalence.

Prevalence of Eyeworms (Nematoda: Thelazioidea) in Beef Cattle Grazing Different Range Pasture Zones in Alberta, Canada

The eyes from 410 beef cattle grazing 6 range pasture zones in Alberta were dissected and examined for species of Thelazia. Thirty-eight (9.3%) contained eyeworms: 25 (6.1%) contained Thelazia skrjabini alone, 3 (0.7%) contained Thelazia gulosa alone, and 10 (2.4%) had a mixed infection of T. skrjabini and T. gulosa. Prevalence was related to the type of pasture. The prevalence was lower in cattle grazing short- and mid-grass pastures (zones 1, 2; 0% and 1.5%, respectively) than those grazing transitional or aspen parkland pastures (zones 3, 5; 7.4% and 6.2%, respectively) or rough fescue or woodland type pastures (zones 4, 6; 11.3% and 18.4%, respectively). The data suggest that prevalence is related to pasture type that limits the number of its vector, Musca autumnalis.

Thelazia lacrymalis in Horses in Kentucky and Observations on the Face Fly (Musca autumnalis) as a Probable Intermediate Host

Eyes from 114 (30.3%) of 376 dead horses, examined from 3 April 1975 to 3 April 1976, were naturally infected with adult Thelazia lacrymalis; 1 horse was also infected with 1 male Thelazia skrijabini. Adult T. lacrymalis from dead horses were successfully transferred mechanically to the eyes of 3 of 4 Shetland ponies raised helminth-free. Larvae from gravid female T. lacrymalis underwent development in experimentally infected, laboratory-raised face flies (Musca autumnalis) and third-stage larvae ranging from 1.82 to 2.94 mm in total length were recovered at 12 to 15 days postexposure. A total of 866 naturally occurring face flies were collected from the head region of horses. Twelve of the face flies harbored larval stages of Thelazia spp. One of the larvae resembled third-stage T. lacrymalis that were recovered from the experimentally infected, laboratory-raised face flies. Introduction of 3 third-stage larvae from 1 face fly onto the cornea of a pony raised helminth-free resulted in the recovery of 1 male T. skrjabini 242 days later. In addition to the eyeworm larvae, other parasites recovered from the face flies included Heterotylenchus autumnalis, hypopi of astigmatid mites and a first instar beetle (Coleoptera: Rhipiphoridae). Data from these investigations indicate the likelihood that face flies are an intermediate host for T. lacrymalis and probably other species of Thelazia in this part of the country.

EYE WORMS OF THE FAMILY THELAZIIDAE FROM BRAZILIAN BIRDS

Eighteen species of three genera of the family Thelaziidae are reported from the eyes of Brazilian birds. Thelazia sicki, T. spizaëli, T. anadorhynchi, and Oxyspirura cameroni are new. A parasite–host list of the species of Thelazia, Oxyspirura, and Ceralospira is included.

Thelazia infection of man and mammals in China

Summary Study of the original material of ocular nematodes from man and the dog in China, as well as material recently secured from a dog and a rabbit in Peking, demonstrates the corectness of Leiper's view that the human and dog specimens from China belong to the species Thelazia callip˦da, and provides evidence that the rabbit is another host of this species of Thelazia. The presence of male worms in the human and in all of the dog material has made it possible to describe this sex in T. callip˦da for the first time. The number of postcloacal papillae in the male worm of this species in smaller than that designated in the original description of the genus Thelizia and, consequently, a slight emendation of the generic concept is required. The record of T. rhodesii from cattle in China is new.