Musca domestica is not a vector of Thelazia callipaeda in experimental or natural conditions

Identification and distribution of some medico-veterinary important pathogens in muscid flies in two geographical regions of Türkiye

Some dipteran flies play an important role in the transmission of pathogens such as viruses, bacteria, fungi, protozoan and metazoan parasites in humans and other animals. Despite this importance, knowledge of the prevalence and molecular characteristics of some pathogens in flies is limited, and no data are available for Türkiye. In this study, we investigated the possible vector role of muscid fly species for the transmission of Enterocytozoon bieneusi Desportes (Chytridiopsida: Enterocytozoonidae), Encephalitozoon spp., Coxiella burnetii Derrick (Legionellales: Coxiellaceae) and Thelazia spp. using polymerase chain reaction (PCR) and sequence analysis. The flies were trapped in different animal-related places and surroundings from two different geographical regions of Türkiye including Central Anatolia and Middle Black Sea. According to the morphological keys, 850 (85%), 141 (14.1%) and 6 (0.6%) of the total of 1000 fly specimens identified as Musca domestica Linnaeus (Diptera: Muscidae), Stomoxys calcitrans Linnaeus (Diptera: Muscidae) and Musca autumnalis De Geer (Diptera: Muscidae), respectively. The other species including Haematobia irritans Linnaeus (Diptera: Muscidae), Muscina stabulans Fallén (Diptera: Muscidae) and Hydrotaea ignava Harris (Diptera: Muscidae) were each represented by a single specimen. Screening of the pathogens identified E. bieneusi only in M. domestica with a prevalence of 2.4%. Sequence analyses identified three known genotypes, Type IV, BEB6 and BEB8, and one novel genotype named AEUEb of E. bieneusi in M. domestica. Coxiella burnetii was detected in M. domestica and S. calcitrans with prevalences of 2.9% and 2.8%, respectively. The one specimen of H. ignava was also positive for C. burnetii. Encephalitozoon spp. and Thelazia spp. were not found in the examined specimens. Our results contribute to the current knowledge on the vector potential of muscid flies and their possible role in the transmission dynamics of certain pathogens, especially in regions where diseases are prevalent and affect public and animal health.

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.

First report of Thelazia callipaeda in a free-ranging Iberian wolf (Canis lupus signatus) from Spain

Thelazia callipaeda (Spirurida, Thelaziidae) is a vector-borne zoonotic eyeworm able to infect a broad spectrum of carnivores. Here, we describe the first case of bilateral infection by T. callipaeda in the eyes of an adult female Iberian wolf (Canis lupus signatus) in central Spain. Nematodes collected were morphologically identified (n = 42), and two specimens were molecularly characterized. At the sequence analysis of the partial mitochondrial cytochrome c oxidase subunit 1 gene, T. callipaeda haplotype 1 (the only haplotype circulating in Europe) was detected. The role of the Iberian wolf as a natural reservoir for T. callipaeda in the life cycle of this emerging zoonosis and the implications in conservation are discussed.

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.

Drosophilidae feeding on animals and the inherent mystery of their parasitism

Insect evolution, from a free to a parasitic lifestyle, took eons under the pressure of a plethora of ecological and environmental drivers in different habitats, resulting in varying degrees of interactions with their hosts. Most Drosophilidae are known to be adapted to feeding on substrates rich in bacteria, yeasts and other microfungi. Some of them, mainly those in the Steganinae subfamily, display a singular behaviour, feeding on animal tissues or secretions. This behaviour may represent an evolving tendency towards parasitism. Indeed, while the predatory attitude is typical for the larval stages of a great proportion of flies within this subfamily, adult males of the genera Amiota, Apsiphortica and Phortica display a clearly zoophilic attitude, feeding on the lachrymal secretions of living mammals (also referred as to lachryphagy). Ultimately, some of these lachryphagous species act as vectors and intermediate hosts for the spirurid nematode Thelazia callipaeda, which parasitizes the eyes of domestic and wild carnivores and also humans. Here we review the scientific information available and provide an opinion on the roots of their evolution towards the parasitic behaviour. The distribution of T. callipaeda and its host affiliation is also discussed and future trends in the study of the ecology of Steganinae are outlined.

Drosophilidae feeding on animals and the inherent mystery of their parasitism

Insect evolution, from a free to a parasitic lifestyle, took eons under the pressure of a plethora of ecological and environmental drivers in different habitats, resulting in varying degrees of interactions with their hosts. Most Drosophilidae are known to be adapted to feeding on substrates rich in bacteria, yeasts and other microfungi. Some of them, mainly those in the Steganinae subfamily, display a singular behaviour, feeding on animal tissues or secretions. This behaviour may represent an evolving tendency towards parasitism. Indeed, while the predatory attitude is typical for the larval stages of a great proportion of flies within this subfamily, adult males of the genera Amiota, Apsiphortica and Phortica display a clearly zoophilic attitude, feeding on the lachrymal secretions of living mammals (also referred as to lachryphagy). Ultimately, some of these lachryphagous species act as vectors and intermediate hosts for the spirurid nematode Thelazia callipaeda, which parasitizes the eyes of domestic and wild carnivores and also humans. Here we review the scientific information available and provide an opinion on the roots of their evolution towards the parasitic behaviour. The distribution of T. callipaeda and its host affiliation is also discussed and future trends in the study of the ecology of Steganinae are outlined.

The first human case of Thelazia callipaeda infection in Vietnam

A 26-year-old man residing in a village of Thai Nguyen Province, North Vietnam, visited the Thai Nguyen Provincial Hospital in July 2008. He felt a bulge-sticking pain in his left eye and extracted 5 small nematode worms by himself half a day before visiting the hospital. Two more worms were extracted from his left eye by a medical doctor, and they were morphologically observed and genetically analyzed on the mitochondrial cytochrome c oxidase 1 gene. The worms were 1 male and 1 female, and genetically identical with those of Thelazia callipaeda. By the present study, the presence of human T. callipaeda infection is first reported in Vietnam.

Competence of the housefly, Musca domestica, as a vector of Microsporum canis under experimental conditions

The role of Musca domestica Linnaeus as a vector of the dermatophyte Microsporum canis was investigated under experimental laboratory conditions. About 400 4-day-old M. domestica flies were divided into two groups. Group A consisted of about 200 infected flies and group B comprised about 200 uninfected flies that were used as controls. Each trial was run three times. Flies from group A were fed for 24 h with a solution of ultra-high temperature-treated (UHT) milk containing about 10(6) colony-forming units (CFU) per mL of M. canis (infected milk inoculum [IMI]). The control group (group B) was fed with only UHT milk spiked with a teaspoon of honey. Microsporum canis was detected from faeces, vomitus, external surfaces and internal organs of 20 adult flies, eggs, first-, second- and third-stage (L1, L2, L3) larvae and pupae of each group, as well from 20 adult newly emerged flies (NEFs; from infected generations only). Samples were collected at 2, 4, 6 and 24 h post-infection (p.i.) (i.e. the times at which IMI was available) and on 2, 5, 7 and 8 days p.i. from adult flies, faeces and vomitus. Eggs, L1, L2, L3 and pupae were processed as soon as they appeared. Equivalent samples were taken from group B. All the samples were individually cultured. Microsporum canis was not isolated from the control group, from eggs, larvae, pupae or NEFs, or from faeces and vomitus, although it was detected on the body surface (26.2%) and internal organs (26.9%) of adult flies. The highest positivity for M. canis was detected on flies within the first 6 h p.i. (i.e. 57.2% on the body surface and 71.6% in the internal organs). No M. canis was isolated at 24 h p.i., but it was isolated from the body surface only at 2 and 5 days p.i. The results presented provide evidence that M. domestica transmits M. canis mechanically with its outer body surface for up to 5 days p.i., but does not do so through its vomitus and faeces or transovarially. The role played by M. domestica in the epidemiology of human and animal dermatophytoses is discussed.

Identification of the intermediate hosts of Habronema microstoma and Habronema muscae under field conditions

A polymerase chain reaction (PCR)-based assay was used for the specific detection of Habronema microstoma and Habronema muscae (Nematoda, Spirurida) in order to identify the intermediate hosts of both nematode species under field conditions. A total of 1087 netted and 165 laboratory-bred flies were tested. Flies were identified as Musca domestica Linnaeus 1758, Musca autumnalis De Geer 1776, Haematobia irritans (Linnaeus 1758), Haematobia titillans (De Geer 1907) and Stomoxys calcitrans (Linnaeus 1758) (Muscidae). Genomic DNA was extracted from pools of fly heads, thoraces and abdomens, and 703 samples were subjected to a duplex two-step semi-nested PCR assay to specifically detect diagnostic regions within the ribosomal ITS2 sequence of both H. microstoma and H. muscae. Stomoxys calcitrans specimens were positive for H. microstoma DNA and M. domestica specimens were positive for H. muscae DNA. In particular, PCR-positive samples derived from both farm-netted and laboratory-bred flies. The present study represents the first evidence of the vectorial competence of different fly species as intermediate hosts of Habronema stomachworms under field conditions. We discuss the roles of S. calcitrans and M. domestica in transmitting H. microstoma and H. muscae.

Phortica variegata as an intermediate host of Thelazia callipaeda under natural conditions: evidence for pathogen transmission by a male arthropod vector

Knowledge about Phortica variegata (Drosophilidae, Steganinae), the intermediate host of the eyeworm Thelazia callipaeda (Spirurida, Thelaziidae), is confined to experimental studies. To investigate the role P. variegata plays in the transmission of T. callipaeda under natural conditions, the population dynamics of these flies in the natural environment and their feeding preferences (on vegetables and/or animal lachrymal secretions) were examined. From April to November 2005, a total number of 969 (557 males and 412 females) P. variegata flies were collected weekly in a region of southern Italy with a history of canine thelaziosis. The flies were identified and dissected or subjected to a PCR assay specific for a region within the ribosomal ITS-1 DNA of T. callipaeda. The zoophilic preferences of P. variegata were assessed by collecting flies around the eyes of a person or around a fruit bait. Seven hundred and twenty flies (398 males and 322 females) were dissected under a stereomicroscope; 249 flies (158 males and 91 females) that died prior to the dissection were subjected to molecular investigation. Only P. variegata males were infected with larval T. callipaeda both at dissection (six, 0.83%) and with the specific PCR (seven, 2.81%), representing a total percentage of 1.34% flies infected. Interestingly, only males were collected around the eyes, compared with a male/female ratio of 1:4 around the fruit. This survey indicated that P. variegata males act as intermediate hosts of T. callipaeda under natural conditions in Europe. Both the zoophilic behaviour of P. variegata males on lachrymal secretions and their role as vector of T. callipaeda have been discussed as they represent a peculiarity in medical and veterinary entomology. The synchrony between the fly population dynamics and the biology of the nematode in the definitive host provides an interesting model for exploring the co-evolution of Thelazia spp. with their hosts.

Nematode biology and larval development of Thelazia callipaeda (Spirurida, Thelaziidae) in the drosophilid intermediate host in Europe and China

Thelazia callipaeda, commonly known as the 'oriental eyeworm', has been recently reported in Italy and other European countries. The insect/s that act as intermediate hosts and details of larval development inside the vector remain unclear. In order to (1) demonstrate the species of fly that may act as vector/s for T. callipaeda in southern Italy (Site A) and China (Site B) and (2) describe the larval development of the nematode in the body of flies, 847 Phortica (Drosophilidae) flies were collected from the above two sites, each with a history of human and/or canine thelaziosis. Flies were identified as Phortica variegata (245 - site A) and Phortica okadai (602 - site B), experimentally infected by 1st-stage larvae (L1), kept at different temperatures and dissected daily until day 180 post-infection (p.i.). Dead flies from site A were subjected to specific polymerase chain reaction (PCR) assay to detect T. callipaeda. To demonstrate the role of Phortica as vectors of T. callipaeda, 3rd-stage larvae (L3) recovered from the proboscis of flies were deposited onto the cornea of the eyes of dogs and rabbits. Following dissection, 3 (2.9%) of P. variegata in site A were found to be infected by L3 in the proboscis on days +14, +21 and +53 p.i., compared with 26 (18.4%) of Phortica flies recorded as being positive by PCR. Sequences from positive PCR products were 99% identical to sequences of the corresponding species available in GenBank (AY207464). At site B, 106 (17.6%) of 602 dissected P. okadai were found to be infected by T. callipaeda larvae (different stages) and in total 62 L3 were recovered from the proboscis of 34 (5.6%) flies. The shortest time in which L3 were found was at day +14, +17, +19, and +50 p.i. respectively, depending on the environmental temperatures. Of 30 flies overwintered for 6 months, 6 L3 were detected at day +180 p.i. in 3 flies (10%). The biology of larval development was reconstructed on the basis of the dissection of 602 P. okadai-infected flies and the morphology of larval stages in the insect body described. The present work provides evidence that P. variegata and P. okadai act as vectors for T. callipaeda in southern Europe and in China, respectively. The phenomenon of overwintering is described here for the first time for T. callipaeda and discussed. Finally, the relationship between T. callipaeda and its fly vector is considered in light of disease prophylaxis and to model its dissemination into habitats and environments favourable to Phortica flies.