Competence of Phortica variegata from the United States as an Intermediate Host of the Thelazia callipaeda Eyeworm

Emergence of Thelaziosis Caused by Thelazia callipaeda in Dogs and Cats, United States

We report 2 autochthonous feline thelaziosis cases caused by the eyeworm Thelazia callipaeda and discuss the spread among dogs in the northeastern United States. Phylogenetic analysis suggests the parasite was introduced from Europe. Adopting a One Health approach is needed to limit further spread of T. callipaeda eyeworms in North America.

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.

Development of Novel Management Tools for Phortica variegata (Diptera: Drosophilidae), Vector of the Oriental Eyeworm, Thelazia callipaeda (Spirurida: Thelaziidae), in Europe

Lachryphagous males of Phortica variegata (Fallén, 1823) are gaining increasing attention in Europe, as they act as vectors of the nematode Thelazia callipaeda Railliet & Henry, 1910, causal agent of thelaziosis, an emergent zoonotic disease. Currently, there are no effective control strategies against the vector, and surveillance and monitoring rely on time-consuming and nonselective sampling methods. Our aim was to improve the knowledge about the population dynamics and the chemical ecology of the species. A total of 5,726 P. variegata flies (96.4% males and 3.6% females, mostly gravid) were collected in field experiments during June-September of 2020 in an oak forest in northern Spain. Our results indicate that 1) by means of sweep netting a significantly higher number of captures were found both around the collector´s body and in the air than at ground level; 2) a positive relationship was detected between the abundance of Phortica flies and temperature, with two significant peaks of abundance at 24 and 33°C; 3) the blend of red wine and cider vinegar was the most attractive bait; 4) yellow traps captured fewer flies compared to black and transparent traps; and 5) a significant reduction toward vinegar and wine was detected in presence of the phenolic monoterpenoid carvacrol. In addition, all the males (n = 690) analyzed by both molecular detection and dissection resulted negative for the presence of T. callipaeda larvae. Overall, these findings provide a better understanding of the vector in terms of monitoring and management strategies.

Autochthonous Thelazia callipaeda Infection in Dog, New York, USA, 2020

We report a case of autochthonous infection of the eye worm Thelazia callipaeda in a dog in the northeastern United States. Integrated morphologic identification and molecular diagnosis confirmed the species. Phylogenetic analysis suggested introduction from Europe. The zoonotic potential of this parasite warrants broader surveillance and increased awareness among physicians and veterinarians.

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.

Survival of Phortica variegata experimentally and naturally infected with Thelazia callipaeda

Knowledge of the effects that Thelazia callipaeda (Spirurida, Thelaziidae) infection has on the survival of its vector Phortica variegata (Drosophilidae, Steganinae) is scarce. The present study aimed to: (a) assess the rate of infection between experimentally infected (EI) and not experimentally infected (NEI) flies and (b) determine how T. callipaeda infection may affect the survival of P. variegata. In addition, fat composition was evaluated in flies that died during overwintering. Molecular analysis showed that T. callipaeda prevalence in flies that died before experimental infection, plus those from the NEI group, is 0.75% (i.e. 11 out of 1462 individuals). The EI group showed a significantly higher positivity to T. callipaeda (i.e. 51 out of 682 individuals; 7.48%) compared with the NEI group (i.e. 9 out of 750 individuals; 1.2%). Thelazia callipaeda DNA was detected until 147 days after experimental infection. This demonstrates that larvae of this eyeworm may survive in the fly for a significant period of the winter. Fat composition analysis showed that flies produced more unsaturated than saturated fatty acids during diapause, probably because unsaturated fatty acids remain in a liquid state at lower temperatures, providing anti-freeze properties to survive winter.

Case Report: Thelazia callipaeda Eye Infection: The First Human Case in Germany

Thelazia callipaeda eye worm is a nematode transmitted by drosophilid flies not only primarily to carnivores and lagomorphs but also to humans. Only a few cases have been reported in Europe (Italy, France, and Portugal). Here, we report the first eye infection in a German patient.

Temperature is a common climatic descriptor of lachryphagous activity period in Phortica variegata (Diptera: Drosophilidae) from multiple geographical locations

Background

The drosophilid Phortica variegata is known as vector of Thelazia callipaeda, the oriental eyeworm native to Asia that has become an emergent zoonotic agent in several European regions. Unlike almost all other arthropod vectors of pathogens, only P. variegata males feed of lachrymal secretions of animals, ingesting first-stage larvae (L1) of the worm living in the orbital cavities of the host, and allowing with the same behaviour the introduction of infective L3. Despite the increased detection of T. callipaeda in many European countries, information about the length of the lachryphagous activity period of P. variegata and a deep knowledge of the environmental and climatic variables involved are still limited.

Methods

We herein present the results of a multicentre study involving five sites from four different countries (Italy, Spain, UK and USA) where canine thelaziosis is endemic and/or where it has already been ascertained the presence of P. variegata. Field data have been obtained on a fortnightly basis from mid-April to the end of November 2018 from a contemporary standardized sampling (same sampling effort and time of collection in all sites) of lachryphagous flies collected around the eyes of a human bait using an entomological net. These data have been associated to data collection of local climatic variables (day length, temperature, wind speed, barometric pressure and relative humidity).

Results

Overall, a total of 4862 P. variegata flies (4637 males and 224 females) were collected, with high differences in densities among the different sampling sites. Significant positive correlations were found between P. variegata male density and temperature and wind speed, while negative correlations were observed for barometric pressure and relative humidity. However, the above significant differences are confirmed in each sampling site separately only for the temperature.

Conclusions

This multicentre study highlights that temperature is the major common environmental driver in describing the lachryphagous activity of P. variegata in Europe and USA and, therefore, the transmission risk of thelaziosis.

Predicting the distribution of Phortica variegata and potential for Thelazia callipaeda transmission in Europe and the United Kingdom

BACKGROUND

Male fruitflies Phortica variegata (Drosophilidae, Steganinae) are the intermediate host of the zoonotic nematode Thelazia callipaeda (Spirurida, Thelaziidae). More than 10 years ago, when T. callipaeda was confined to remote regions of southern Italy, ecological niche models were used to predict the potential distribution of P. variegata across Europe and the likely risk of the nematode spreading through infected dogs travelling to/from endemic regions. As predicted, over the last 10 years T. callipaeda has spread rapidly across Europe. Recently, we identified the potential for its introduction to the UK through infected dogs travelling to/from endemic regions of mainland Europe.

METHODS

Here updated information is used to re-evaluate the model-predicted European, and specifically, UK distribution to determine the likelihood of T. callipaeda becoming established. Additionally, the UK distribution of P. variegata was further investigated through snapshot fly trapping at model-predicted locations.

RESULTS

Ecological niche modelling using Genetic Algorithm for Rule-set Prediction (GARP) analysis suggests a European range similar to that described previously, with some indication of potential spread further eastward. Finer scale UK mapping suggested that P. variegata presence was limited mostly to southern England, but highlighted regions where P. variegata has not been documented previously. The arbitrary fly trapping identified activity of P. variegata at two locations where the species has been found previously late in the season. No specimens were collected at model-predicted locations, although habitat suitable for the species was identified.

CONCLUSIONS

GARP-model prediction of P. variegata distribution suggests presence of suitable conditions in previously undocumented regions of the UK and Europe and highlight the possibility for further spread of T. callipaeda across Europe, including the UK. Further work to validate the P. variegata UK model with field data will help improve its accuracy in predicting suitable areas, whilst surveillance of sylvatic definitive host species in such locations is advised to monitor for evidence of autochthonous T. callipaeda transmission.