Culicoides biting midges, arboviruses and public health in Europe

Preliminary investigation reveals novel pathological consequences of bluetongue virus-1 infection in the endocrine glands of pregnant Indian sheep

Bluetongue virus (BTV), a major peril to the sheep industry, infects a wide range of the cells in the infected animals including mononuclear, dendritic and epithelial cells. However, little is known about its tropism for the secretory epithelial cells of endocrine glands and the pathogenesis it induces. The aim of the study was to assess the BTV load, antigen distribution in the tissue of the pituitary, thyroid as well as adrenal glands and associated histopathological consequences. BTV antigens were localized using immunohistochemistry in the thyroid's epithelial cells, zona fasciculata and zona reticularis cells and the anterior pituitary epithelial cells. The real-time PCR portrayed the high viral load in adrenals at 7th days postinoculation (DPI) and in thyroid and pituitary glands at 15th DPI. Serum examination revealed variation in the T-3 and T-4 of infected animals in comparison to the control group. Caspase-3 immunolocalization revealed BTV-1 induces apoptosis in the affected cells of endocrine gland of infected animals. Further, this study signifies the tropism of BTV in the novel sites (endocrine glands) of the host that might be one of the reasons for the poor performance of infected animals.

Culicoides biting midges feeding behaviour as a key for understanding avian Haemoproteus transmission in Lithuania

Investigations of host feeding behaviour in haematophagous insects are critical to assess transmission routes of vector-borne diseases. Understanding if a certain species has ornithophilic or mammalophilic feeding behaviour can facilitate future studies focused on pathogens transmission to and from certain host species. Culicoides Latreille (Diptera: Ceratopogonidae) are vectors of several pathogens, which include arboviruses, bacteria and parasites to a considerable diversity of vertebrate hosts. However, most of the studies focused on feeding habits target Culicoides species that could transmit the Bluetongue virus, consequently with a mammalophilic feeding behaviour, leaving aside the Culicoides species that are involved in the transmission of vector-borne parasites to birds, such as Haemoproteus Kruse (Haemosporida: Haemoproteidae). This study aimed to investigate the source of blood meals of wild-caught Culicoides using molecular-based methods and to correlate our findings with the reports of Haemoproteus parasites in Culicoides species. Engorged Culicoides females were collected using ultraviolet (UV)-light traps at seven different localities in Lithuania in 2021-2023. Biting midges were dissected, and the abdomens of engorged females were used for molecular investigation of the blood meal source. A polymerase chain reaction (PCR) protocol that amplifies a fragment of the Cytochrome B gene of vertebrates was used. Obtained sequences were compared to available information in GenBank database to confirm the source of the blood meal. In total, 258 engorged Culicoides females, representing nine different species, were analysed. The source of blood meal was identified in 29.1% of them with most of the insects having fed on birds (74.7%) and the remaining on mammals (25.3%). Culicoides segnis Campbell, Pelham-Clinton was the only species to feed exclusively on birds; Culicoides from the Obsoletus group, C. pallidicornis Kieffer and C. punctatus Latreille were found to feed exclusively on mammals; C. festivipennis Kieffer, C. kibunensis Tokunaga and C. pictipennis Staeger had an opportunistic feeding behaviour, with the first two preferably feeding on birds. Due to their feeding behaviour and the presence of Haemoproteus parasites reported in the literature, C. festivipennis, C. kibunensis, C. pictipennis, and C. segnis play an important role in the transmission of those avian vector-borne parasite in the wild. These Culicoides species were already confirmed as being able to support the development of several Haemoproteus species and lineages. Future studies focused on understanding the epidemiology of avian pathogens transmitted by Culicoides should target these species.

Sampling of Culicoides with nontraditional methods provides unusual species composition and new records for southern Spain

BACKGROUND

Culicoides midges have been well-studied in Spain, particularly over the last 20 years, mainly because of their role as vectors of arboviral diseases that affect livestock. Most studies on Culicoides are conducted using suction light traps in farmed environments, but studies employing alternative trapping techniques or focusing on natural habitats are scarce.

METHODS

In the present study, we analyze Culicoides captured in 2023 at 476 sites in western Andalusia (southern Spain) using carbon dioxide-baited Biogents (BG)-sentinel traps across different ecosystems.

RESULTS

We collected 3,084 Culicoides midges (3060 females and 24 males) belonging to 23 species, including the new species Culicoides grandifovea sp. nov. and the first record of Culicoides pseudolangeroni for Europe. Both species were described with morphological and molecular methods and detailed data on spatial distribution was also recorded. The new species showed close phylogenetic relations with sequences from an unidentified Culicoides from Morocco (92.6% similarity) and with Culicoides kurensis. Culicoides imicola was the most abundant species (17.4%), followed by Culicoides grandifovea sp. nov. (14.6%) and Culicoides kurensis (11.9%). Interestingly, Culicoides montanus was the only species of the obsoletus and pulicaris species complexes captured, representing the first record of this species in southern Spain. A total of 53 valid Culicoides species have been reported in the area, with 48 already reported in literature records and 5 more added in the present study. Information on the flight period for the most common Culicoides species is also provided.

CONCLUSIONS

To the best of our knowledge, our study represents the most comprehensive effort ever done on nonfarmland habitats using carbon-dioxide baited suction traps for collecting Culicoides. Our data suggests that using carbon dioxide traps offers a completely different perspective on Culicoides communities compared with routinely used light traps, including the discovery of previously unrecorded species.

Climate correlates of bluetongue incidence in southern Portugal

Model forecasts of the spatiotemporal occurrence dynamics of diseases are necessary and can help understand and thus manage future disease outbreaks. In our study, we used ecological niche modelling to assess the impact of climate on the vector suitability for bluetongue disease, a disease affecting livestock production with important economic consequences. Specifically, we investigated the relationship between the occurrence of bluetongue outbreaks and the environmental suitability of each of the four vector species studied. We found that the main vector for bluetongue disease, Culicoides imicola, a typically tropical and subtropical species, was a strong predictor for disease outbreak occurrence in a region of southern Portugal from 2004 to 2021. The results highlight the importance of understanding the climatic factors that might influence vector presence to help manage infectious disease impacts. When diseases impact economically relevant species, the impacts go beyond mortality and have important economic consequences.

Oropouche fever cases diagnosed in Italy in two epidemiologically non-related travellers from Cuba, late May to early June 2024

Oropouche fever is caused by Oropouche virus (OROV), transmitted primarily through the bite of infected midges, particularly of the genus Culicoides. The virus is mainly circulating in Central and South America where several countries reported an ongoing outbreak. We report here two imported cases of OROV infection identified in Italy, late May-early June 2024. These cases indicate that in the shadow of a massive dengue outbreak in the Americas, the Oropouche outbreak might be more widespread than previously estimated.

Ecological niche modelling of Culicoides imicola and future range shifts under climate change scenarios in Italy

Culicoides imicola is the main vector of viral diseases of livestock in Europe such as bluetongue (BT), African horse sickness and epizootic haemorrhagic disease. Climatic factors are the main drivers of C. imicola occurrence and its distribution might be subject to rapid shifts due to climate change. Entomological data, collected during BT surveillance, and climatic/environmental variables were used to analyse ecological niche and to model C. imicola distribution and possible future range shifts in Italy. An ensemble technique was used to weigh the performance of machine learning, linear and profile methods. Updated future climate projections from the latest phase of the Climate Model Intercomparison Project were used to generate future distributions for the next three 20-year periods, according to combinations of general circulation models and shared socioeconomic pathways and considering different climate change scenarios. Results indicated the minimum temperature of the coldest month (BIO 6) and precipitation of the driest-warmest months (BIO 14) as the main limiting climatic factors. Indeed, BIO 6 and BIO 14 reported the two highest values of variable importance, respectively, 9.16% (confidence interval [CI] = 7.99%-10.32%), and 2.01% (CI = 1.57%-2.44%). Under the worst-case scenario of climate change, C. imicola range is expected to expand northward and shift away from the coasts of central Italy, while in some areas of southern Italy, environmental suitability will decrease. Our results provide predictions of C. imicola distribution according to the most up-to-date future climate projections and should be of great use to surveillance management at regional and national scales.

First report of Culicoides caucoliberensis in Spain: Exploring molecular phylogeny, host-feeding behaviour and avian haemosporidian parasites

Culicoides biting midges (Diptera: Ceratopogonidae) are vectors of pathogens that affect wildlife and livestock. Understanding the composition and distribution of vector species is crucial for implementing control strategies and preventing the spread of infectious diseases. This study provides a morphological and molecular characterisation of Culicoides caucoliberensis, which represents the first record for Spain, increasing the number of Culicoides species in the country to 85. A total of 213 specimens were collected using Onderstepoort-ultraviolet down-draught light traps on a rocky coastline in the Balearic Islands during two sampling periods in 2022. Phylogenetic analysis showed that C. caucoliberensis forms a monophyletic cluster within the Maritimus group. Host preferences were determined for the first time and showed propensity to feed on the European shag (Phalacrocorax aristotelis). The vector role of C. caucoliberensis for haemosporidian transmission remains unclear since molecular detection of Haemosporidians (Haemoproteus and Plasmodium) was negative for all the pools of parous and engorged females analysed. This study emphasises the importance of conducting entomofauna studies in lesser-known Mediterranean islet landscapes and highlights the need for research on vectors within the One Health framework.

Visualisation of Bluetongue Virus in the Salivary Apparatus of Culicoides Biting Midges Highlights the Accessory Glands as a Primary Arboviral Infection Site

BACKGROUND

Arthropods transmit a wide range of pathogens of importance for the global health of humans, animals, and plants. One group of these arthropod vectors, Culicoides biting midges (Diptera: Ceratopogonidae), is the biological vector of several human and animal pathogens, including economically important livestock viruses like bluetongue virus (BTV). Like other arthropod-borne viruses (arboviruses), Culicoides-borne viruses must reach and replicate in the salivary apparatus, from where they can be transmitted to susceptible hosts through the saliva during subsequent blood feeding. Despite the importance of the salivary gland apparatus for pathogen transmission to susceptible animals from the bite of infected Culicoides, these structures have received relatively little attention, perhaps due to the small size and fragility of these vectors.

RESULTS

In this study, we developed techniques to visualize the infection of the salivary glands and other soft tissues with BTV, in some of the smallest known arbovirus vectors, Culicoides biting midges, using three-dimensional immunofluorescence confocal microscopy. We showed BTV infection of specific structures of the salivary gland apparatus of female Culicoides vectors following oral virus uptake, related visualisation of viral infection in the salivary apparatus to high viral RNA copies in the body, and demonstrated for the first time, that the accessory glands are a primary site for BTV replication within the salivary apparatus.

CONCLUSIONS

Our work has revealed a novel site of virus-vector interactions, and a novel role of the accessory glands of Culicoides in arbovirus amplification and transmission. Our approach would also be applicable to a wide range of arbovirus vector groups including sand flies (Diptera: Psychodidae), as well as provide a powerful tool to investigate arbovirus infection and dissemination, particularly where there are practical challenges in the visualization of small size and delicate tissues of arthropods.

Outlook on RNAi-Based Strategies for Controlling Culicoides Biting Midges

Culicoides are small biting midges with the capacity to transmit important livestock pathogens around much of the world, and their impacts on animal welfare are likely to expand. Hemorrhagic diseases resulting from Culicoides-vectored viruses, for example, can lead to millions of dollars in economic damages for producers. Chemical insecticides can reduce Culicoides abundance but may not suppress population numbers enough to prevent pathogen transmission. These insecticides can also cause negative effects on non-target organisms and ecosystems. RNA interference (RNAi) is a cellular regulatory mechanism that degrades mRNA and suppresses gene expression. Studies have examined the utility of this mechanism for insect pest control, and with it, have described the hurdles towards producing, optimizing, and applying these RNAi-based products. These methods hold promise for being highly specific and environmentally benign when compared to chemical insecticides and are more transient than engineering transgenic insects. Given the lack of available control options for Culicoides, RNAi-based products could be an option to treat large areas with minimal environmental impact. In this study, we describe the state of current Culicoides control methods, successes and hurdles towards using RNAi for pest control, and the necessary research required to bring an RNAi-based control method to fruition for Culicoides midges.

Metavirome Analysis and Identification of Midge-Borne Viruses from Yunnan Province, China, in 2021

Midges are widely distributed globally and can transmit various human and animal diseases through blood-sucking. As part of this study, 259,300 midges were collected from four districts in Yunnan province, China, to detect the viral richness and diversity using metavirome analysis techniques. As many as 26 virus families were detected, and the partial sequences of bluetongue virus (BTV), dengue virus (DENV), and Getah virus (GETV) were identified by phylogenetic analysis and PCR amplification. Two BTV gene fragments, 866 bps for the VP2 gene of BTV type 16 and 655 bps for the VP5 gene of BTV type 21, were amplified. The nucleotide sequence identities of the two amplified BTV fragments were 94.46% and 98.81%, respectively, with two classical BTV-16 (GenBank: JN671907) and BTV-21 strains (GenBank: MK250961) isolated in Yunnan province. Furthermore, the BTV-16 DH2021 strain was successfully isolated in C6/36 cells, and the peak value of the copy number reached 3.13 × 107 copies/μL after five consecutive BHK-21 cell passages. Moreover, two 2054 bps fragments including the E gene of DENV genotype Asia II were amplified and shared the highest identity with the DENV strain isolated in New Guinea in 1944. A length of 656 bps GETV gene sequence encoded the partial capsid protein, and it shared the highest identity of 99.68% with the GETV isolated from Shandong province, China, in 2017. Overall, this study emphasizes the importance of implementing prevention and control strategies for viral diseases transmitted by midges in China.

Topical, contact, and oral susceptibility of adult Culicoides biting midges (Diptera: Ceratopogonidae) to fluralaner

BACKGROUND

Culicoides biting midges (Diptera: Ceratopogonidae) are economically important blood-feeding pests closely associated with livestock production. They are the principal vectors of two hemorrhagic disease viruses affecting both wild and domestic ruminants within the US: bluetongue virus (BTV) and epizootic hemorrhagic disease virus (EHDV). BTV impacts the US agriculture sector through direct commodity loss and strict international livestock trade restrictions. Yet, despite posing a considerable threat to US livestock, Culicoides are understudied, and management strategies are lacking. Current control tools for Culicoides are limited to synthetic chemicals, predominantly pyrethroids. With limited products available for livestock producers, proper pesticide rotation is difficult. The present study investigates the efficacy of fluralaner, an isoxazoline insecticide, beyond its current labeled use as an ectoparasiticide in anticipation of adding a new class of pesticides into rotation for use against biting midges.

METHODS

The efficacy of fluralaner was evaluated by conducting contact, topical, and oral toxicity bioassays on adult female Culicoides sonorensis. Contact toxicity was assessed by using a modified WHO cone assay, which simulates exposure through landing on an insecticide-treated surface. A modified WHO topical toxicity assay, in which fluralaner dilutions were administered to the lateral thorax, was used to assess topical toxicity. For evaluation of oral toxicity, females were offered a blood meal spiked with fluralaner in an artificial membrane feeding system to simulate a systemic insecticide.

RESULTS

Contact exposure of fluralaner did not cause extensive or consistent mortality. Even the highest concentration tested (100 mg/ml) resulted in an average of only 24.3% mortality at 24 h, and mortality did not significantly differ between exposed and control midges at any concentration. One hundred percent mortality was consistently achieved at concentrations of 1 mg/ml when fluralaner was applied topically. The LC50 for topical exposure to fluralaner at 24 h was estimated to be 0.011 mg/ml. Oral exposure to fluralaner through ingestion of a spiked blood meal proved to be the most effective exposure method, significantly increasing mortality in a dose-dependent manner at 1 h post-exposure. The LC50 at 24 h following ingestion was 14.42 ng/ml.

CONCLUSION

Our results suggest that fluralaner is a viable candidate for use as an insecticide against adult biting midges if exposed orally, such as in a systemic given to livestock. As withdrawal period requirements for meat animals present unique yet definitive challenges, pharmacokinetic studies of isoxazoline drugs need to be pursued and finalized for livestock before fluralaner may be used as a management strategy in this manner. Alternatively, livestock not raised for consumption, such as hair sheep, would directly benefit from administering oral fluralaner as a component of a BTV disease management program.

First evidence of schmallenberg virus infection in southern Italy

BACKGROUND

Schmallenberg virus (SBV) is a vector-borne pathogen that mainly affects ruminants. Schmallenberg disease has never been described in southern Italy, although this geographic area displays climatic features suitable for Culicoides biting midges, which transmit the pathogen. An observational study was carried out in the Campania region in 2020 to evaluate the seroprevalence in cattle and water buffalo as well as to identify the risk factors involved in the distribution of SBV.

RESULTS

Relatively high seroprevalences of 38.2% (cattle) and 43% (water buffalo) were found by using a commercial SBV ELISA, which is comparable to the prevalence obtained in other countries under post-epidemic conditions. A virus neutralization assay performed on positive samples showed high titers in a large percentage of animals which is assumed to indicate recent exposure. Bivariate analysis of several variables revealed some environmental factors associated with higher seroprevalence, such as mean annual temperature, distance from the coast, and altitude. Multivariate logistic regression confirmed the statistical association only for mean annual temperature, that was found to be the main factor responsible for the distribution of the virus in southern Italy. In addition, molecular diagnosis attempts were performed on serum samples and resulted in the detection of SBV RNA in two herds and six animals.

CONCLUSIONS

In this work we have demonstrated the circulation of SBV in southern Italy using both molecular and serological assays. This study emphasized the essential role of monitoring in preventing the re-emergence of vector-borne diseases in ruminants.

Culicoides jiangchengensis, a new species of the subgenus Sinocoides (Diptera, Ceratopogonidae) based on integrative taxonomy from China

Biting midges of the genus Culicoides are important in both medicine and veterinary medicine because their blood-feeding regime enable them to transmit a variety of pathogens. In this study, the morphological characteristics of the new species of Culicoides (Sinocoides) jiangchengensis Wang et Liu sp. nov are described and compared with the other species of female Culicoides in the subgenus Sinocoides. Three morphological characteristics of C. jiangchengensis, such as without sensory pit in 3rd palpus segment, sensilla coeloconica on flagellomeres 1,9-13, and m1 and m2 cell of the wings with pale spots, were different from the other nine species of culicoides in subgenus Sinocoides. Genetically, C. jiangchengensis are most closely related to C. malipoensis, but they were located in different branches and the minimum interspecific distance between them was 12.6%. In addition, a checklist of 10 species in the subgenus Sinocoides Chu, 1983 (Diptera: Ceratopogonidae: Culicoides) in China, including the new species C. jiangchengensis Wang et Liu sp. nov., is provided, and an updated key to species of the subgenus Sinocoides Chu, 1983 was presented.

An Agent-Based Model of Biting Midge Dynamics to Understand Bluetongue Outbreaks

Bluetongue (BT) is a well-known vector-borne disease that infects ruminants such as sheep, cattle, and deer with high mortality rates. Recent outbreaks in Europe highlight the importance of understanding vector-host dynamics and potential courses of action to mitigate the damage that can be done by BT. We present an agent-based model, entitled 'MidgePy', that focuses on the movement of individual Culicoides spp. biting midges and their interactions with ruminants to understand their role as vectors in BT outbreaks, especially in regions that do not regularly experience outbreaks. The results of our sensitivity analysis suggest that midge survival rate has a significant impact on the probability of a BTV outbreak as well as its severity. Using midge flight activity as a proxy for temperature, we found that an increase in environmental temperature corresponded with an increased probability of outbreak after identifying parameter regions where outbreaks are more likely to occur. This suggests that future methods to control BT spread could combine large-scale vaccination programs with biting midge population control measures such as the use of pesticides. Spatial heterogeneity in the environment is also explored to give insight on optimal farm layouts to reduce the potential for BT outbreaks.

Abundance and diversity of Culicoides Latreille (Diptera: Ceratopogonidae) in southern Ontario, Canada

BACKGROUND

Culicoides Latreille (Diptera: Ceratopogonidae) is a genus of hematophagous midges feeding on various vertebrate hosts and serving as a vector for numerous pathogens important to livestock and wildlife health. North American pathogens include bluetongue (BT) and epizootic hemorrhagic disease (EHD) viruses. Little is known about Culicoides spp. distribution and abundance and species composition in Ontario, Canada, despite bordering numerous U.S. states with documented Culicoides spp. and BT and EHD virus activity. We sought to characterize Culicoides spp. distribution and abundance and to investigate whether select meteorological and ecological risk factors influenced the abundance of Culicoides biguttatus, C. stellifer, and the subgenus Avaritia trapped throughout southern Ontario.

METHODS

From June to October of 2017 to 2018, CDC-type LED light suction traps were placed on twelve livestock-associated sites across southern Ontario. Culicoides spp. collected were morphologically identified to the species level when possible. Associations were examined using negative binomial regression among C. biguttatus, C. stellifer, and subgenus Avaritia abundance, and select factors: ambient temperature, rainfall, primary livestock species, latitude, and habitat type.

RESULTS

In total, 33,905 Culicoides spp. midges were collected, encompassing 14 species from seven subgenera and one species group. Culicoides sonorensis was collected from three sites during both years. Within Ontario, the northern trapping locations had a pattern of seasonal peak abundance in August (2017) and July (2018), and the southern locations had abundance peaks in June for both years. Culicoides biguttatus, C. stellifer, and subgenus Avaritia were significantly more abundant if ovine was the primary livestock species at trapping sites (compared to bovine). Culicoides stellifer and subgenus Avaritia were significantly more abundant at mid- to high-temperature ranges on trap days (i.e., 17.3-20.2 and 20.3-31.0 °C compared to 9.5-17.2 °C). Additionally, subgenus Avaritia were significantly more abundant if rainfall 4 weeks prior was between 2.7 and 20.1 mm compared to 0.0 mm and if rainfall 8 weeks prior was between 0.1 and 2.1 mm compared to 0.0 mm.

CONCLUSIONS

Results from our study describe Culicoides spp. distribution in southern Ontario, the potential for spread and maintenance of EHD and BT viruses, and concurrent health risks to livestock and wildlife in southern Ontario in reference to certain meteorological and ecological risk factors. We identified that Culicoides spp. are diverse in this province, and appear to be distinctly distributed spatially and temporally. The livestock species present, temperature, and rainfall appear to have an impact on the abundance of C. biguttatus, C. stellifer, and subgenus Avaritia trapped. These findings could help inform targeted surveillance, control measures, and the development of management guides for Culicoides spp. and EHD and BT viruses in southern Ontario, Canada.

The First Serological Detection and Risk Factors Analysis of Akabane Virus in Egyptian Cattle

Akabane virus (AKAV) is an insect-borne virus belonging to the genus Orthobunyavirus of the family Peribunyaviridae. It is the etiologic agent of Akabane disease (AD), which emerged in Asia, Australia, and the Middle East causing severe economic losses among domestic and wild animals. AKAV has not received enough attention in Egypt, and its evidence among Egyptian animals has never been reported. Therefore, this study used ELISA assay to investigate the seroprevalence of AKAV among Egyptian dairy and beef cattle in eight localities of Beheira province, north Egypt. Out of 368 investigated plasma samples, the overall AKAV seroprevalence was 54.3% (95% CI: 50.8-61.4). AKAV antibodies were detected in all examined cattle farms (7/7) and the majority of abattoirs (8/9). Age, sex, breed, and location of the tested cattle were analyzed as risk factors for AKAV infection. A higher significant increase in seropositivity was obtained in cattle who were aged >5 years (p < 0.0001; OR = 9.4), females (p < 0.0001, OR = 8.3), or Holstein breed (p < 0.0001, OR = 22.6) than in younger ages, males, and Mixed and Colombian zebu breeds, respectively. Moreover, a significant variation in AKAV seroprevalence between the tested locations was noticed. Ultimately, a multivariable analysis concluded that age (p = 0.002, OR = 3.32, 95% CI = 1.57-7.04) and breed (p = 0.03, OR = 1.69, 95% CI = 1.05-2.72) were significant risks for AKAV infection. In conclusion, this study is the first to detect AKAV infection in Egyptian animals.

Biting midges (Diptera: Ceratopogonidae) as putative vectors of zoonotic Onchocerca lupi (Nematoda: Onchocercidae) in northern Arizona and New Mexico, southwestern United States

Onchocerca lupi (Rodonaja, 1967) is an understudied, vector-borne, filarioid nematode that causes ocular onchocercosis in dogs, cats, coyotes, wolves, and is also capable of infecting humans. Onchocercosis in dogs has been reported with increasing incidence worldwide. However, despite the growing number of reports describing canine O. lupi cases as well as zoonotic infections globally, the disease prevalence in endemic areas and vector species of this parasite remains largely unknown. Here, our study aimed to identify the occurrence of O. lupi infected dogs in northern Arizona, New Mexico, and Utah, United States and identify the vector of this nematode. A total of 532 skin samples from randomly selected companion animals with known geographic locations within the Navajo Reservation were collected and molecularly surveyed by PCR for the presence of O. lupi DNA (September 2019-June 2022) using previously published nematode primers (COI) and DNA sequencing. O. lupi DNA was detected in 50 (9.4%) sampled animals throughout the reservation. Using positive animal samples to target geographic locations, pointed hematophagous insect trapping was performed to identify potential O. lupi vectors. Out of 1,922 insects screened, 38 individual insects and 19 insect pools tested positive for the presence of O. lupi, all of which belong to the Diptera family. This increased surveillance of definitive host and biological vector/intermediate host is the first large scale prevalence study of O. lupi in companion animals in an endemic area of the United States, and identified an overall prevalence of 9.4% in companion animals as well as multiple likely biological vector and putative vector species in the southwestern United States. Furthermore, the identification of these putative vectors in close proximity to human populations coupled with multiple, local zoonotic cases highlight the One Health importance of O. lupi.

Would Climate Change Influence the Potential Distribution and Ecological Niche of Bluetongue Virus and Its Main Vector in Peru?

Bluetongue virus (BTV) is an arbovirus that is transmitted between domestic and wild ruminants by Culicoides spp. Its worldwide distribution depends on competent vectors and suitable environmental ecosystems that are becoming affected by climate change. Therefore, we evaluated whether climate change would influence the potential distribution and ecological niche of BTV and Culicoides insignis in Peru. Here, we analyzed BTV (n = 145) and C. insignis (n = 22) occurrence records under two shared socioeconomic pathway scenarios (SSP126 and SSP585) with five primary general circulation models (GCMs) using the kuenm R package v.1.1.9. Then, we obtained binary presence–absence maps and represented the risk of transmission of BTV and niche overlapping. The niche model approach showed that north and east Peru presented suitability in the current climate scenario and they would have a decreased risk of BTV, whilst its vector would be stable and expand with high agreement for the five GCMs. In addition, its niche overlap showed that the two niches almost overlap at present and would completely overlap with one another in future climate scenarios. These findings might be used to determine the areas of highest priority for entomological and virological investigations and surveillance in order to control and prevent bluetongue infections in Peru.

Emerging parasites and vectors in a rapidly changing world: from ecology to management

Global changes have influenced our societies in several ways with both positive (e.g., technology, transportation, and food security), and negative impacts (e.g., mental health problems, spread of diseases, and pandemics). Overall, these changes have affected the distribution patterns of parasites and arthropod vectors with the introduction and spreading of alien species in new geographical areas, eventually posing new challenges in public health. In this framework, the Acta Tropica Special Issue "Emerging parasites and vectors in a rapidly changing world: from ecology to management" provides a focus on the biology, ecology and management of emerging parasites and vectors of human and veterinary importance. Herein we review and discuss novel studies dealing with interactions of parasites and vectors with animals in changing environmental settings. In our opinion, a special focus on the implementation of management strategies of parasitic diseases to face anthropogenic environmental changes still represent a priority for public health. In the final section, key research challenges in this rapidly changing scenario are outlined.

Intravenous Infection of Small Ruminants Suggests a Goat-Restricted Host Tropism and Weak Humoral Immune Response for an Atypical Bluetongue Virus Isolate

Bluetongue virus (BTV) is the etiologic agent of bluetongue (BT), a viral WOAH-listed disease affecting wild and domestic ruminants, primarily sheep. The outermost capsid protein VP2, encoded by S2, is the virion's most variable protein, and the ability of reference sera to neutralize an isolate has so far dictated the differentiation of 24 classical BTV serotypes. Since 2008, additional novel BTV serotypes, often referred to as "atypical" BTVs, have been documented and, currently, the full list includes 36 putative serotypes. In March 2015, a novel atypical BTV strain was detected in the blood of asymptomatic goats in Sardinia (Italy) and named BTV-X ITL2015. The strain re-emerged in the same region in 2021 (BTV-X ITL2021). In this study, we investigated the pathogenicity and kinetics of infection of BTV-X ITL2021 following subcutaneous and intravenous infection of small ruminants. We demonstrated that, in our experimental settings, BTV-X ITL2021 induced a long-lasting viraemia only when administered by the intravenous route in goats, though the animals remained healthy and, apparently, did not develop a neutralizing immune response. Sheep were shown to be refractory to the infection by either route. Our findings suggest a restricted host tropism of BTV-X and point out goats as reservoirs for this virus in the field.

Effects of storage conditions and digestion time on DNA amplification of biting midge (Culicoides) blood meals

BACKGROUND

Molecular analysis of blood meals is increasingly used to identify the hosts of biting insects such as midges and mosquitoes. Successful host identification depends on the availability of sufficient host DNA template for PCR amplification, making it important to understand how amplification success changes under different storage conditions and with different durations of blood meal digestion within the insect gut before being placed into the storage medium.

METHOD

We characterised and compared the digestion profile of two species of Culicoides over a 96-h period using a novel set of general vertebrate primers targeting the 16S rRNA gene. A set number of individuals from each species were killed over 13 time points post-blood feeding and preserved in 95% ethanol. Samples were stored either at ambient room temperature or in a - 20 °C freezer to examine the effect of storage condition on the PCR amplification success of host DNA.

RESULTS

We found that amplification success across the 96-h sampling period post-feeding was reduced from 96 to 6% and 96% to 14% for Culicoides nubeculosus and Culicoides sonorensis, respectively. We found no effect of storage condition on PCR amplification success, and storage in 95% ethanol was sufficient to maintain high rates of amplifiable host DNA for at least 9 months, even at room temperature.

CONCLUSIONS

These findings highlight the limited time frame during which an individual may contain amplifiable host DNA and demonstrate the importance of timely sample capture and processing post-blood feeding. Moreover, storage in 95% ethanol alone is sufficient to limit host DNA degradation. These results are relevant to the design of studies investigating the biting behaviour and disease transmission potential of Culicoides and other biting Diptera.

Wing morphology variations in Culicoides circumscriptus from France

The biting midge Culicoides circumscriptus Kieffer, 1918 is a European widespread vector of avian malaria throughout the continent and is a possible vector of Akabane virus and Bluetongue virus. This species populates a wide range of environments in contrasting ecological settings often exposed to strong seasonal fluctuations. The main goals of this study were to investigate C. circumscriptus phenotypic variation at three departments in France (Corsica Island, Moselle and Var) and to determine if its phenotypes vary with the environment. Culicoides circumscriptus wing phenotypes were analyzed using a geometric morphometric approach based on anatomical landmarks and outlines of the wing. Dendogram trees based on landmarks and the outlines-2 set (cell m4) showed similar topologies and separated populations of C. circumscriptus. In contrast, another set of outlines-1 (covering the r-m cross vein, M, radiale and arculus) presented a different hierarchical clustering tree. The phenotypic variation observed in C. circumscriptus indicated that these populations are exposed to environmental and ecological pressures. Our results suggest the presence of phenotypic plasticity in this species.

Arbovirus Epidemiology: The Mystery of Unnoticed Epidemics in Ghana, West Africa

It is evident that all the countries surrounding Ghana have experienced epidemics of key arboviruses of medical importance, such as the recent dengue fever epidemic in Burkina Faso. Therefore, Ghana is considered a ripe zone for epidemics of arboviruses, mainly dengue. Surprisingly, Ghana never experienced the propounded deadly dengue epidemic. Indeed, it is mysterious because the mosquito vectors capable of transmitting the dengue virus, such as Aedes aegypti, were identified in Ghana through entomological investigations. Additionally, cases may be missed, as the diagnostic and surveillance capacities of the country are weak. Therefore, we review the arbovirus situation and outline probable reasons for the epidemic mystery in the country. Most of the recorded cases of arbovirus infections were usually investigated via serology by detecting IgM and IgG immunoglobulins in clinical samples, which is indicative of prior exposure but not an active case. This led to the identification of yellow fever virus and dengue virus as the main circulating arboviruses among the Ghanaian population. However, major yellow fever epidemics were reported for over a decade. It is important to note that the reviewed arboviruses were not frequently detected in the vectors. The data highlight the necessity of strengthening the diagnostics and the need for continuous arbovirus and vector surveillance to provide an early warning system for future arbovirus epidemics.

Insight on Bluetongue virus transmission in small ruminants in Senegal

Bluetongue (BT) is an infectious, arthropod-borne viral disease of domestic and wild ruminants. The disease causes animal mortality, production decrease and commercial limits for herds. Despite the active circulation of the disease in the world, few studies have been carried out in Senegal. The objective of this study was to assess the current prevalence of BT in small ruminants and the serotypes circulating in Senegal. A cross-sectional study was conducted in the fourteen regions of Senegal. After the sampling campaign, sera collected in sheep and goats herds were screened for the presence of Bluetongue virus (BTV) specific antibodies using c-Elisa. The whole blood of seropositive animals was further analyzed by RT-qPCR and positive samples were typed to identify BTV serotypes. Analysis of several risk factors such as age, sex and species of animals was performed using logistic regression. The overall seroprevalence of BTV in Senegal was 72.6% (95% CI: 70.3-74.9%) with 75.9% (95% CI: 72.2-79.5%) in goat and 70.6% (95% CI: 67.5-73.6%) in sheep. Female (prevalence=77.1%) and adult (prevalence=80%) animals showed the highest seropositivity to BTV compared respectively to male (55.7%, p=6.133e-09) and young (49.4%, p < 2.2e-16). The RT-qPCR results showed the presence of BT viral genome in 359 small ruminants. The results obtained from serological and genotyping studies showed an active spread of the Bluetongue virus in domestic ruminants and phylogenetic analysis showed that the BTV-2 is one of the circulating serotypes in Senegal. This study allows having baseline information for controlling Bluetongue in Senegal.

Modeling the spatial distribution of Culicoides species (Diptera: Ceratopogonidae) as vectors of animal diseases in Ethiopia

Culicoides biting midges (Diptera: Ceratopogonidae) are the major vectors of bluetongue, Schmallenberg, and African horse sickness viruses. This study was conducted to survey Culicoides species in different parts of Ethiopia and to develop habitat suitability for the major Culicoides species in Ethiopia. Culicoides traps were set in different parts of the country from December 2018 to April 2021 using UV light Onderstepoort traps and the collected Culicoides were sorted to species level. To develop the species distribution model for the two predominant Culicoides species, namely Culicoides imicola and C. kingi, an ensemble modeling technique was used with the Biomod2 package of R software. KAPPA True skill statistics (TSS) and ROC curve were used to evaluate the accuracy of species distribution models. In the ensemble modeling, models which score TSS values greater than 0.8 were considered. Negative binomialregression models were used to evaluate the relationship between C. imicola and C. kingi catch and various environmental and climatic factors. During the study period, a total of 9148 Culicoides were collected from 66 trapping sites. Of the total 9148, 8576 of them belongs to seven species and the remaining 572 Culicoides were unidentified. The predominant species was C. imicola (52.8%), followed by C. kingi (23.6%). The abundance of these two species was highly influenced by the agro-ecological zone of the capture sites and the proximity of the capture sites to livestock farms. Climatic variables such as mean annual minimum and maximum temperature and mean annual rainfall were found to influence the catch of C. imicola at the different study sites. The ensemble model performed very well for both species with KAPPA (0.9), TSS (0.98), and ROC (0.999) for C. imicola and KAPPA (0.889), TSS (0.999), and ROC (0.999) for C. kingi. Culicoides imicola has a larger suitability range compared to C. kingi. The Great Rift Valley in Ethiopia, the southern and eastern parts of the country, and the areas along the Blue Nile and Lake Tana basins in northern Ethiopia were particularly suitable for C. imicola. High suitability for C. kingi was found in central Ethiopia and the Southern Nations, Nationalities and Peoples Region (SNNPR). The habitat suitability model developed here could help researchers better understand where the above vector-borne diseases are likely to occur and target surveillance to high-risk areas.

New Distribution Records of Biting Midges of the Genus Culicoides (Diptera: Ceratopogonidae) Latreille, Culicoides bergi and Culicoides baueri, in Southern Ontario, Canada

Some species of Culicoides Latreille (Diptera: Ceratopogonidae) can be pests as well as pathogen vectors, but data on their distribution in Ontario, Canada, are sparse. Collecting this baseline data is important given ongoing, accelerated alterations in global climate patterns that may favor the establishment of some species in northern latitudes. Culicoides spp. were surveyed using UV light traps over two seasons in 2017 and 2018 at livestock farms in southern Ontario, Canada. Two Culicoides spp. not previously recorded in Canada were identified, C. bergi and C. baueri, representing new country and provincial records. Unlike some congenerics, these two species are not currently recognized as vectors of pathogens that pose a health risk to humans, livestock or wildlife in North America. However, the possibility that these Culicoides species may have recently expanded their geographic range, potentially in association with climate and/or landscape changes, warrants ongoing attention and research. Furthermore, our results provoke the question of the potential undocumented diversity of Culicoides spp. in Ontario and other parts of Canada, and whether other Culicoides spp. may be undergoing range expansion. The current and future distributions of Culicoides spp., and other potential vectors of human, agricultural, and wildlife health significance, are important to identify for proper disease risk assessment, mitigation, and management.

Emergence dynamics of adult Culicoides biting midges at two farms in south-east England

Background

Culicoides biting midges (Diptera: Ceratopogonidae) are biological vectors of livestock arboviruses that cause diseases with significant economic, social and welfare impacts. Within temperate regions, livestock movement during arbovirus outbreaks can be facilitated by declaring a ‘seasonal vector-free period’ (SVFP) during winter when adult Culicoides are not active. In this study we carry out long-term monitoring of Culicoides adult emergence from larval development habitats at two farms in the UK to validate current definitions of the SVFP and to provide novel bionomic data for known vector species.

Methods

Standard emergence traps were used to collect emerging adult Culicoides from dung heaps at two cattle farms in the south-east of England from June to November 2016 and March 2017 to May 2018. Culicoides were morphologically identified to species or complex level and count data were analysed using a simple population dynamic model for pre-adult Culicoides that included meteorological components.

Results

More than 96,000 Culicoides were identified from 267 emergence trapping events across 2 years, revealing clear evidence of bivoltinism from peaks of male populations of Culicoidesobsoletus emerging from dung heaps. This pattern was also reflected in the emergence of adult female Obsoletus complex populations, which dominated the collections (64.4% of total catch) and emerged throughout the adult active period. Adult male C. obsoletus were observed emerging earlier than females (protandry) and emergence of both sexes occurred throughout the year. Culicoides chiopterus and Culicoides scoticus were also identified in spring emergence collections, providing the first evidence for the overwintering of larvae in dung heaps for these species.

Conclusions

This study demonstrates continual and highly variable rates of emergence of Culicoides throughout the year. A lack of evidence for mass emergence in spring along with the ability to observe male generations highlights the need for complementary surveillance techniques in addition to light-trap data when investigating seasonality and phenology. Evidence was found of other vector species, C. chiopterus and C. scoticus, utilising cattle dung heaps as an overwintering habitat, further highlighting the importance of these habitats on farms.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-022-05370-z.

Composition and diversity of Culicoides biting midges (Diptera: Ceratopogonidae) in rural and suburban environments of Algeria

Culicoides biting midges are well known biological vectors of several arboviruses causing more than 100 veterinary and medical diseases worldwide. In Algeria, bluetongue virus, which is transmitted by Culicoides midges, is responsible for one of the most critical insect-borne diseases of sheep. For example, this disease caused clinically severe morbidity of about 2,661 confirmed cases out of 21,175 susceptible sheep in Algeria. This study compared the abundance, richness, and diversity of Culicoides species in rural and suburban environments of semi-arid regions in North Africa. It examined the potential influence of the bio-climatic factors on the variation of population sizes and the elevation distribution of biting midges. Specimen collection was carried out from June to September during two successive years (2018 and 2019) using CDC light traps installed at 15 sites in different environments. Culicoides specimens were dissected, slide-mounted, and morphologically identified using the interactive identification key IIKC and various standard morphological criteria. A total of 1,046 Culicoides specimens (1,024 females and 22 males) were trapped and classified into 22 species, belonged to nine distinct subgenera. Two new species records for Algeria and even North Africa are reported: Culicoides albicans (Winnertz, 1852) and Culicoides nubeculosus (Meigen, 1830). Culicoides newsteadi Austen, 1921 (51.6%) was the dominant species, and it was followed by Culicoides punctatus (Meigen, 1804) (16.3%) and Culicoides odiatus Austen, 1921 (11.5%). These three species, comprising 80% of the collected Culicoides, were the most abundant both outside and inside livestock stables in rural and suburban environments. Species diversity was similar in the two settings, with a slight increase in suburban environments. None of the Culicoides species encountered correlated significantly with the climatic factors (mean temperature, precipitation, and relative humidity). Elevation was the most determinant environmental parameter that affected the abundance and distribution of Culicoides midges in the semi-arid and sub-humid areas studied. The maximum distribution of Culicoides species was detected at mid elevations (400‒800 m). Using a modeling approach, we explored for the first time the variation of composition and diversity in Culicoides communities within different climatic regions, environments and livestock settings in Algeria. This survey deepens our understanding of the relationships among environmental factors, abundance, diversity, and geographic distribution of Culicoides. This is a crucial step to assess the epidemiological situation of the diseases transmitted by these biting midges and to allow mitigation of the associated risks.

Culicoides species community composition and feeding preferences in two aquatic ecosystems in northern Spain

Background

Aquatic ecosystems provide breeding sites for blood-sucking insects such as Culicoides biting midges (Diptera: Ceratopogonidae), but factors affecting their distribution and host choice are poorly understood. A study was undertaken at two nature reserves in northern Spain to examine the abundance, species composition, population dynamics and feeding patterns of biting midges between 2018 and 2019.

Methods

Culicoides were captured by light suction traps baited with CO₂ and by sweep netting vegetation. Blood meals and species identification of blood-fed specimens were determined using cytochrome c oxidase I subunit (COI) DNA barcoding. Multivariate generalized linear models were used to evaluate the associations between the abundance of Culicoides, the species richness and other parameters.

Results

The 4973 identified specimens comprised 28 species of Culicoides. These included two species reported for the first time in northern Spain, thus raising to 54 the number of Culicoides species described in the region. Specimens of all 28 species and 99.6% of the total specimens collected were caught in suction traps, while sweep netting vegetation revealed just 11 species and 0.4% of the total specimens. Midge abundance peaked in June/early July, with five species comprising > 80% of the captures: Culicoides alazanicus (24.9%), Culicoides griseidorsum (20.3%), Culicoides poperinghensis (16.2%), Culicoides kibunensis (10.7%) and Culicoides clastrieri (9.6%). DNA barcode analysis of blood meals from eight Culicoides species revealed that they fed on 17 vertebrate species (3 mammals and 14 birds). Species in the subgenus Avaritia were primarily ornithophilic, except for C. griseidorsum and C. poperinghensis. Host DNA from blood meals was successfully amplified from 75% of blood-fed females. A pictorial blood meal digestion scale is provided to accurately assess the blood-fed status of female Culicoides.

Conclusions

The large number of different blood meal sources identified in the midges captured in this study signals the likely importance of wild birds and mammals (e.g. red deer and wild boar) as reservoir/amplifying hosts for pathogens. Available hosts are more exposed to being bitten by biting midge populations in aquatic ecosystems in late spring and early summer.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-022-05297-5.

A Survey on Native and Invasive Mosquitoes and Other Biting Dipterans in Northern Spain

PURPOSE

Haematophagous Diptera, such as mosquitoes (Culicidae), biting midges (Ceratopogonidae), and black flies (Simuliidae), are important insects for public and animal health due to their capacity to bite and transmit pathogens. Outdoor recreation areas are usually affected by biting species and provide suitable habitats to both adult and immature stages. This study aimed to determine the species diversity and larval sites of these Diptera groups in two golf courses.

METHODS

A multi-method collection approach using ultraviolet-CDC traps, human landing catches, collection in breeding sites, and ovitraps was implemented during summer 2020 in northern Spain. Insects were determined by morphological features accompanied by DNA barcoding.

RESULTS

A total of ten native mosquito species were recorded either as adults or as larval stages. The invasive species Aedes japonicus was collected only at egg or pupa stage in ovitraps. Culex pipiens s.l. and Culex torrentium were both common mosquito species accounting for 47.9% of the total larval site collections and their larvae might be found in a wide range of natural and artificial sites. Culiseta longiareolata specimens were also prominent (30.1% of the total) and occurred exclusively in man-made water-filled containers. A total of 13 Culicoides species were identified, 10 of which were captured by ultraviolet-CDC traps, particularly members of the Obsoletus complex (Culicoides obsoletus/Culicoides scoticus, 74.9%) and seven species by emergence traps, being the two most abundant C. kibunensis (44.8%) and C. festivipennis (34.9%). Simulium cryophilum was also collected hovering around the operator under field sampling.

CONCLUSION

A comprehensive representation of the blood-sucking Diptera fauna and their larval sites was obtained by the multi-method approach in two Spanish golf courses.

Habitat-dependent Culicoides species composition and abundance in blue tit (Cyanistes caeruleus) nests

Wild birds are hosts of Culicoides from as early on as the nesting stage when constrained to their nests. However, the environmental factors which determine the abundance and composition of Culicoides species within each bird nest are still understudied. We sampled Culicoides from Eurasian blue tit (Cyanistes caeruleus) nests found in 2 types of forests located in southern Spain. Firstly, we monitored the abundance of Culicoides species in bird nests from a dry Pyrenean oak deciduous forest and a humid mixed forest comprising Pyrenean and Holm oaks throughout 2 consecutive years. During the 3rd year, we performed a cross-fostering experiment between synchronous nests to differentiate the role of rearing environment conditions from that of the genetically determined or maternally transmitted cues released by nestlings from each forest. We found 147 female Culicoides from 5 different species in the birds' nests. The abundance of Culicoides was higher in the dry forest than in the humid forest. Culicoides abundance, species richness and prevalence were greater when the nestlings were hatched later in the season. The same pattern was observed in the cross-fostering experiment, but we did not find evidence that nestling's features determined by the forest of origin had any effect on the Culicoides collected. These results support the notion that habitat type has a strong influence on the Culicoides affecting birds in their nests, while some life history traits of birds, such as the timing of reproduction, also influence Culicoides abundance and species composition.

Culicoides segnis and Culicoides pictipennis Biting Midges (Diptera, Ceratopogonidae), New Reported Vectors of Haemoproteus Parasites

As bloodsuckers of birds, Culicoides biting midges (Diptera, Ceratopogonidae) play an important role in the transmission of avian haemosporidian (Haemoproteus) parasites, which are prevalent in many bird populations and cause disease, pathology, or even mortality in their hosts. Information about the role of the various Culicoides species in the transmission of Haemoproteus parasites remains insufficient. This presents an obstacle for the better understanding of the epizootiology of haemoproteosis. The aim of this study was to determine new Culicoides species involved in the transmission of Haemoproteus parasites in the wild. Biting midges were collected using UV traps on the Curonian Spit, Lithuania. Only parous Culicoides females were investigated: they were identified and were diagnosed for the presence of Haemoproteus parasites using both microscopy and PCR-based methods. We collected and dissected 420 parous Culicoides females. PCR-based screening showed that 28 parous Culicoides biting midges were infected with avian Haemoproteus parasites. Haemoproteid DNA was detected in Culicoides kibunensis, Culicoides pictipennis, Culicoides festivipennis, Culicoides segnis, Culicoides pallidicornis, and Culicoides obsoletus biting midges. The DNA of Haemoproteus palloris, genetic lineage hWW1, was found for the first time in C. pallidicornis. Haemoproteus sporozoites were detected in the salivary glands of two Culicoides segnis biting midges. According to the PCR results, one female contained Haemoproteus tartakovskyi (genetic lineage hHAWF1) DNA and another Haemoproteus majoris (genetic lineage hCCF5) DNA. The sporozoites of Haemoproteus parasites were also detected in the salivary glands of four C. pictipennis biting midges using microscopy, and this finding was confirmed by PCR as Haemoproteus parabelopolskyi DNA (genetic lineage hSYAT02) was detected in three out of the four biting midges. The obtained results supplement existing information about Culicoides biting midges as natural vectors of Haemoproteus spp. and add two new Culicoides species to the vector list, showing the low specificity of these parasites for the invertebrate hosts.

Effect of Constant Temperatures on Culicoides sonorensis Midge Physiology and Vesicular Stomatitis Virus Infection

Simple Summary

Culicoides biting midges are nuisance pests of livestock and well-known vectors of veterinary arboviruses, such as vesicular stomatitis virus (VSV). Female midges ingest viruses when feeding on blood to obtain protein for egg-laying. After ingesting a VSV-infected blood meal, the environmental temperature of the resting location mediates the rates at which blood is digested, eggs are laid, and virus particles are replicated inside the midge. VSV transmission will occur if the timing of virus amplification aligns with the next feeding–egg-laying cycle. We evaluated the impact of constant environmental temperatures on midge physiology (lifespan and reproduction), vector competence for VSV (infection and dissemination), and thermal resting preference. Our results indicate that after ingesting a blood meal, most midges prefer to rest in areas that fall within their preferred physiological range regardless of the temperatures at which they were being maintained. These preferred temperatures maximized their survival, the number of egg-laying cycles, and the likelihood of VSV transmission. Our temperature approach shows that in the Culicoides–VSV system, the preferred resting temperature selected by blood-fed midges is beneficial for both insect and virus transmission.

Abstract

Culicoides midges play an important role in vesicular stomatitis virus (VSV) transmission to US livestock. After VSV-blood feeding, blood digestion followed by oviposition occurs while ingested virus particles replicate and disseminate to salivary glands for transmission during subsequent blood-feeding events. Changes to environmental temperature may alter the feeding–oviposition–refeeding cycles, midge survival, VSV infection, and overall vector capacity. However, the heterothermic midge may respond rapidly to environmental changes by adjusting their thermal behavior to resting in areas closer to their physiological range. Here we investigated the effects of four constant environmental temperatures (20, 25, 30, and 35 °C) on C. sonorensis survival, oviposition, and VSV infection, as well as resting thermal preferences after blood-feeding. We found that most midges preferred to rest in areas at 25–30 °C. These two constant temperatures (25 and 30 °C) allowed an intermediate fitness performance, with a 66% survival probability by day 10 and oviposition cycles occurring every 2–3 days. Additionally, VSV infection rates in bodies and heads with salivary glands were higher than in midges held at 20 °C and 35 °C. Our results provide insight into the implications of temperature on VSV–Culicoides interactions and confirm that the range of temperature preferred by midges can benefit both the vector and the arbovirus.

Dissecting the Species-Specific Virome in Culicoides of Thrace

Biting midges (Culicoides) are vectors of arboviruses of both veterinary and medical importance. The surge of emerging and reemerging vector-borne diseases and their expansion in geographical areas affected by climate change has increased the importance of understanding their capacity to contribute to novel and emerging infectious diseases. The study of Culicoides virome is the first step in the assessment of this potential. In this study, we analyzed the RNA virome of 10 Culicoides species within the geographical area of Thrace in the southeastern part of Europe, a crossing point between Asia and Europe and important path of various arboviruses, utilizing the Ion Torrent next-generation sequencing (NGS) platform and a custom bioinformatics pipeline based on TRINITY assembler and alignment algorithms. The analysis of the RNA virome of 10 Culicoides species resulted in the identification of the genomic signatures of 14 novel RNA viruses, including three fully assembled viruses and four segmented viruses with at least one segment fully assembled, most of which were significantly divergent from previously identified related viruses from the Solemoviridae, Phasmaviridae, Phenuiviridae, Reoviridae, Chuviridae, Partitiviridae, Orthomyxoviridae, Rhabdoviridae, and Flaviviridae families. Each Culicoides species carried a species-specific set of viruses, some of which are related to viruses from other insect vectors in the same area, contributing to the idea of a virus-carrier web within the ecosystem. The identified viruses not only expand our current knowledge on the virome of Culicoides but also set the basis of the genetic diversity of such viruses in the area of southeastern Europe. Furthermore, our study highlights that such metagenomic approaches should include as many species as possible of the local virus-carrier web that interact and share the virome of a geographical area.

First Report of Culicoides Biting Midges (Diptera: Ceratopogonidae) Attacking People in Italy, With the Description of Extreme Larval Breeding Sites and Diurnal Activity of Culicoides riethi

Biting midges of the genus Culicoides (Diptera: Ceratopogonidae) play a paramount role in medical and veterinary entomology worldwide, particularly as vectors of pathogens which cause animal diseases. Biting midges are also infamous for the nuisance they provoke to people involved in outdoor activities. Nonetheless, attacks to man by midges from any Culicoides species have not been reported in Italy. An entomological investigation was performed following repeated attacks to man in a nature park near Rome (central Italy). The study area is a natural degassing zone, characterized by widespread hazardous gas emissions of CO2 and H2S, with several water bodies including permanent lakes, ponds, and pools. The biting midge C. riethi Kieffer, 1914 was very active during daytime in the period April-June. The species has been identified as responsible for attacks on people in the area. An in-depth analysis of the extreme environmental conditions revealed the ability of larvae to thrive in several water bodies, characterized by an extremely low pH and a high concentration of sulfates.

Predicting the possibility of African horse sickness (AHS) introduction into China using spatial risk analysis and habitat connectivity of Culicoides

African horse sickness (AHS) is a devastating equine infectious disease. On 17 March 2020, it first appeared in Thailand and threatened all the South-East Asia equine industry security. Therefore, it is imperative to carry out risk warnings of the AHS in China. The maximum entropy algorithm was used to model AHS and Culicoides separately by using climate and non-climate variables. The least cost path (LCP) method was used to analyze the habitat connectivity of Culicoides with the reclassified land cover and altitude as cost factors. The models showed the mean area under the curve as 0.918 and 0.964 for AHS and Culicoides. The prediction result map shows that there is a high risk area in the southern part of China while the habitats of the Culicoides are connected to each other. Therefore, the risk of introducing AHS into China is high and control of the border area should be strengthened immediately.

A Qualitative Risk Assessment for Bluetongue Disease and African Horse Sickness: The Risk of Entry and Exposure at a UK Zoo

Bluetongue virus (BTV) and African horse sickness virus (AHSV) cause economically important diseases that are currently exotic to the United Kingdom (UK), but have significant potential for introduction and onward transmission. Given the susceptibility of animals kept in zoo collections to vector-borne diseases, a qualitative risk assessment for the introduction of BTV and AHSV to ZSL London Zoo was performed. Risk pathways for each virus were identified and assessed using published literature, animal import data and outputs from epidemiological models. Direct imports of infected animals, as well as wind-borne infected Culicoides, were considered as routes of incursion. The proximity of ongoing disease events in mainland Europe and proven capability of transmission to the UK places ZSL London Zoo at higher risk of BTV release and exposure (estimated as low to medium) than AHSV (estimated as very low to low). The recent long-range expansion of AHSV into Thailand from southern Africa highlights the need for vector competence studies of Palearctic Culicoides for AHSV to assess the risk of transmission in this region.

Morphological and molecular differentiation between Culicoides oxystoma and Culicoides kingi (Diptera: Ceratopogonidae) in Tunisia

Background

Culicoides kingi and Culicoides oxystoma belong to the Schultzei group of biting midges. These two species are vectors of disease in livestock of economic importance. As described in the literature, morphological identification for discrimination between them is still unclear. However, species-specific identification is necessary to solve taxonomic challenges between species and to understand their roles in disease transmission and epidemiology. This study aims to develop accurate tools to discriminate C. oxystoma from C. kingi using traditional morphometry and polymerase chain reaction-restriction fragment length polymorphism (PCR RFLP) assays for use in developing countries.

Methods

Specimens were collected from the region of Kairouan in central Tunisia. A total of 446 C. oxystoma/C. kingi individuals were identified using traditional morphometric analyses combined with PCR–RFLP of the cytochrome c oxidase subunit I gene. Thirteen morphometric measurements were performed from the head, wings, and abdomen of slide-mounted specimens, and six ratios were calculated between these measurements. Multivariate analyses of the morphometric measurements were explored to identify which variables could lead to accurate species identification.

Results

Four variables, namely antennae, wings, spermathecae, and palpus length, were suitable morphometric characteristics to differentiate between the species. Digestion with the SspI restriction enzyme of the PCR product led to good discriminative ability. Molecular procedures and phylogenetic analysis confirmed the efficiency of this simple and rapid PCR–RFLP method.

Conclusions

This study highlights for the first time in Tunisia the presence of C. oxystoma and its discrimination from C. kingi using abdominal measurements and the PCR–RFLP method. This approach could be applied in future epidemiological studies at the national and international levels.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-021-05084-8.

Profiling of RNA Viruses in Biting Midges (Ceratopogonidae) and Related Diptera from Kenya Using Metagenomics and Metabarcoding Analysis

Vector-borne diseases (VBDs) cause enormous health burden worldwide, as they account for more than 17% of all infectious diseases and over 700,000 deaths each year. A significant number of these VBDs are caused by RNA virus pathogens. Here, we used metagenomics and metabarcoding analysis to characterize RNA viruses and their insect hosts among biting midges from Kenya. We identified a total of 15 phylogenetically distinct insect-specific viruses. These viruses fall into six families, with one virus falling in the recently proposed negevirus taxon. The six virus families include Partitiviridae, Iflaviridae, Tombusviridae, Solemoviridae, Totiviridae, and Chuviridae. In addition, we identified many insect species that were possibly associated with the identified viruses. Ceratopogonidae was the most common family of midges identified. Others included Chironomidae and Cecidomyiidae. Our findings reveal a diverse RNA virome among Kenyan midges that includes previously unknown viruses. Further, metabarcoding analysis based on COI (cytochrome c oxidase subunit 1 mitochondrial gene) barcodes reveal a diverse array of midge species among the insects used in the study. Successful application of metagenomics and metabarcoding methods to characterize RNA viruses and their insect hosts in this study highlights a possible simultaneous application of these two methods as cost-effective approaches to virus surveillance and host characterization. IMPORTANCE The majority of the viruses that currently cause diseases in humans and animals are RNA viruses, and more specifically arthropod-transmitted viruses. They cause diseases such as dengue, West Nile infection, bluetongue disease, Schmallenberg disease, and yellow fever, among others. Several sequencing investigations have shown us that a diverse array of RNA viruses among insect vectors remain unknown. Some of these could be ancient lineages that could aid in comprehensive studies on RNA virus evolution. Such studies may provide us with insights into the evolution of the currently pathogenic viruses. Here, we applied metagenomics to field-collected midges and we managed to characterize several RNA viruses, where we recovered complete and nearly complete genomes of these viruses. We also characterized the insect host species that are associated with these viruses. These results add to the currently known diversity of RNA viruses among biting midges as well as their associated insect hosts.

Summer seasonal prevalence of Culicoides species from pre-alpine areas in Switzerland

Biting midges (Diptera: Ceratopogonidae) are arthropods of veterinary importance since they can transmit pathogens and cause severe allergic dermatitis in horses. Very little is known about the species at higher altitudes and their seasonal dynamics. In this work, adult Culicoides were collected with Onderstepoort UV-light suction traps (OVI) from June to September 2016 at two areas situated at around 1600 m asl (pre-alpine area I, 2 farms) and 2030 m asl (pre-alpine area II, 1 farm) in the Canton of Grisons (south-east Switzerland). Overall, 17 049 Culicoides were collected, including 871 parous females. A total of 50 individuals/trap/night (n = 1050) were identified to species (17 species) by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) or by polymerase chain reaction (PCR) and sequencing. The remaining 15 128 Culicoides were classified to species groups' level. Culicoides obsoletus (Meigen, 1818), a multivoltine species, was mainly present at 1600 m asl, whereas at high altitudes (2030 m asl), C. grisescens Edwards, 1939 I&II were the most abundant species. In particular, C. grisescens II, which seems to be univoltine, occurred later in the season but significantly increasing over time. Species diversity was higher at pre-alpine I area (n = 16 species) compared to pre-alpine II (n = 10 species).

A Review of Dung Beetle Introductions in the Antipodes and North America: Status, Opportunities, and Challenges

Following the introduction of cattle, exotic dung beetles (Coleoptera: Aphodiidae, Geotrupidae, Scarabaeidae) were imported into the Antipodes (Australia and New Zealand) and North America (primarily the United States) to accelerate the degradation of cattle dung on pastures. The history of dung beetle introductions between the two regions is similar but has not previously been assessed: this is important as new introductions are continuing in the regions. Here, we review these introduction programs, report on their current status, and discuss methodological advances. In doing so, we examine the accidental introduction of exotic (i.e., adventive) species and the contribution of both deliberately introduced and adventive species to endemic dung beetle faunas. Further, we provide a list of pest and parasite species whose populations can be reduced by dung beetle activity. We also identify a combined total of 37 introduced and 47 adventive dung beetle species that have become established in the Antipodes and North America, with exotic species dominating dung beetle assemblages from pasture habitats. Climatic and edaphic matches, the size of founding populations, abiotic and biotic stressors, and the time of year when releases are made are all critical determinants that affect the success of dung beetle introduction programs. Finally, we discuss opportunities, plus the risks and challenges associated with dung beetle introductions. We hope that this review will aid in the success of future introduction programs, either to enhance ecosystem services in areas that they are needed, or potentially to reestablish native species in regions where they have been extirpated.

Contrasting responses of native ant communities to invasion by an ant invader, Linepithema humile

Invasive alien species pose a serious threat to the integrity and function of natural ecosystems. Understanding how these invaders alter natural communities is therefore an important aspect in predicting the likely future outcomes of biological invasions. Many studies have documented the consequences of invasive alien species on native community structure, through the displacement and local extinction of native species. However, sampling methods and intensities are rarely standardised across such studies, meaning that it is not clear whether differences in response among native communities to the same invader species are due to biological differences between the invaded regions, or differences in the methodologies used. Here we use a matched sampling methodology to compare the effects of the Argentine ant (Linepithema humile Mayr) on native ant community assemblages in two distinct biogeographical regions that share similar ecologies: Girona (Spain) and Jonkershoek Nature Reserve (South Africa). We found a strong negative association between L. humile presence and native ant species richness within both geographic regions. However, the effects differed between the two study regions: in Girona, a single native ant species (Plagiolepis pygmaea) persisted in invaded sites; by contrast, substantially more native ant species persisted at invaded sites in Jonkershoek Nature Reserve. In addition, in Jonkershoek Nature Reserve, the abundance of certain native species appeared to increase in the presence of L. humile. This study therefore demonstrates the potential variable effects of an invasive species in contrasting locations within different biogeographical regions. Future work should explore the causes of this differential resistance among communities and expand standardised sampling approaches to more invaded zones to further explore how local biotic or abiotic conditions of a region determine the nature and extent of impact of L. humile invasion on native ant communities.

Blood meal analysis: host-feeding patterns of biting midges (Diptera, Ceratopogonidae, Culicoides Latreille) in Slovakia

Biting midges of the genus Culicoides are vectors of important pathogens affecting domestic and wild animals and have played a major role in the re-emergence of new outbreaks of bluetongue (BTV) and Schmallenberg (SBV) viruses in Europe. To determine vector-host specificity, trophic preference from blood meal analysis is of major importance in the surveillance of arthropod-borne diseases. Of 28,752 specimens collected, we identified 17 Culicoides species and investigated a total of 48 host sequences from the blood meals. Culicoides obsoletus/C. scoticus, C. dewulfi, C. pulicaris, C. lupicaris, C. punctatus, C. newsteadi, C. riethi, and C. furcillatus were found to feed on mammals (cattle, horses, and humans), birds (domestic chickens), small rodents (Apodemus flavicollis), and hares (Lepus europaeus). To our knowledge, this is the first study investigating trophic preferences of Culicoides spp. in Slovakia. This study demonstrated that Culicoides species are able to feed on domesticated host vertebrates as well as birds, rodents, and humans.

The utilisation of CytB and COI barcodes for the identification of bloodmeals and Culicoides species (Diptera: Ceratopogonidae) reveals a variety of novel wildlife hosts in South Africa

Biting midges in the genus Culicoides (Diptera; Ceratopogonidae) are vectors of pathogens that can cause diseases of major economic importance in humans and animals. Identifying host ranges of these biting midges might aid in understanding the complex epidemiology of such diseases, often involving reservoir hosts and multiple species. In this study, we aim to identify bloodmeal origin from engorged female Culicoides biting midges. All bloodfed females were opportunistically collected as part of an ongoing surveillance programme using Onderstepoort light traps in two provinces in South Africa. DNA of individuals was extracted and subjected to PCR targeting the cytochrome B (CytB) gene region of mammals and avians as well as cytochrome oxidase I (COI) for species identification. In total, 21 new reference barcodes were generated for C. bedfordi, C imicola, C. leucosticus, C. magnus, and C. pycnostictus. Seventy-four blood meals were identified, originating from 12 mammal and three avian species. COI sequence data performed well for species delimitation and 54 Culicoides specimens were identified with C. imicola the predominant species identified (41.8%). Generally, Culicoides species feed on a variety of hosts and host availability might be an important factor when selecting a host. Culicoides species thus appear to be opportunistic feeders rather than specialists. This implicates Culicoides as transfer vectors and demonstrates possible transmission routes of arboviruses and other pathogens from wildlife onwards to domestic animals and humans.

Impacts of Infectious Dose, Feeding Behavior, and Age of Culicoides sonorensis Biting Midges on Infection Dynamics of Vesicular Stomatitis Virus

Culicoides sonorensis biting midges are biological vectors of vesicular stomatitis virus (VSV) in the U.S. Yet, little is known regarding the amount of ingested virus required to infect midges, nor how their feeding behavior or age affects viral replication and vector competence. We determined the minimum infectious dose of VSV-New Jersey for C. sonorensis midges and examined the effects of multiple blood-feeding cycles and age at the time of virus acquisition on infection dynamics. A minimum dose of 3.2 logs of virus/mL of blood resulted in midgut infections, and 5.2 logs/mL resulted in a disseminated infection to salivary glands. For blood-feeding behavior studies, ingestion of one or two non-infectious blood meals (BM) after a VSV infectious blood meal (VSV-BM) resulted in higher whole-body virus titers than midges receiving only the single infectious VSV-BM. Interestingly, this infection enhancement was not seen when a non-infectious BM preceded the infectious VSV-BM. Lastly, increased midge age at the time of infection correlated to increased whole-body virus titers. This research highlights the epidemiological implications of infectious doses, vector feeding behaviors, and vector age on VSV infection dynamics to estimate the risk of transmission by Culicoides midges more precisely.

Experimental transmission of Leishmania (Mundinia) parasites by biting midges (Diptera: Ceratopogonidae)

Leishmania parasites, causative agents of leishmaniasis, are currently divided into four subgenera: Leishmania, Viannia, Sauroleishmania and Mundinia. The recently established subgenus Mundinia has a wide geographical distribution and contains five species, three of which have the potential to infect and cause disease in humans. While the other Leishmania subgenera are transmitted exclusively by phlebotomine sand flies (Diptera: Psychodidae), natural vectors of Mundinia remain uncertain. This study investigates the potential of sand flies and biting midges of the genus Culicoides (Diptera: Ceratopogonidae) to transmit Leishmania parasites of the subgenus Mundinia. Sand flies (Phlebotomus argentipes, P. duboscqi and Lutzomyia migonei) and Culicoides biting midges (Culicoides sonorensis) were exposed to five Mundinia species through a chicken skin membrane and dissected at specific time intervals post bloodmeal. Potentially infected insects were also allowed to feed on ear pinnae of anaesthetized BALB/c mice and the presence of Leishmania DNA was subsequently confirmed in the mice using polymerase chain reaction analyses. In C. sonorensis, all Mundinia species tested were able to establish infection at a high rate, successfully colonize the stomodeal valve and produce a higher proportion of metacyclic forms than in sand flies. Subsequently, three parasite species, L. martiniquensis, L. orientalis and L. sp. from Ghana, were transmitted to the host mouse ear by C. sonorensis bite. In contrast, transmission experiments entirely failed with P. argentipes, although colonisation of the stomodeal valve was observed for L. orientalis and L. martiniquensis and metacyclic forms of L. orientalis were recorded. This laboratory-based transmission of Mundinia species highlights that Culicoides are potential vectors of members of this ancestral subgenus of Leishmania and we suggest further studies in endemic areas to confirm their role in the lifecycles of neglected pathogens.

Leishmania parasites are causative agents of leishmaniasis, a disease affecting millions of humans worldwide. It is widely accepted that these flagellates are transmitted exclusively by phlebotomine sand flies (Diptera: Phlebotominae). Reservoir hosts and insect vectors for the newly established Leishmania subgenus Mundinia, however, remain poorly understood. Preliminary evidence from field-based studies discovered biting midges (Diptera: Ceratopogonidae) that were naturally infected by L. (Mundinia) macropodum in Australia. This surprising finding led us to carry out a detailed laboratory study aimed at comparison of the development of all currently known species of the subgenus Mundinia in both putative vector families. We found that all five Mundinia species developed successfully in C. sonorensis and the successful transmission of three Mundinia species from infected insects to mice was demonstrated for the first time. This is the first detailed in vivo evidence that biting midges can act as competent vectors of Leishmania parasites of the subgenus Mundinia and has considerable epidemiological implications for control of these neglected pathogens.

Orthobunyaviruses: From Virus Binding to Penetration into Mammalian Host Cells

With over 80 members worldwide, Orthobunyavirus is the largest genus in the Peribunyaviridae family. Orthobunyaviruses (OBVs) are arthropod-borne viruses that are structurally simple, with a trisegmented, negative-sense RNA genome and only four structural proteins. OBVs are potential agents of emerging and re-emerging diseases and overall represent a global threat to both public and veterinary health. The focus of this review is on the very first steps of OBV infection in mammalian hosts, from virus binding to penetration and release of the viral genome into the cytosol. Here, we address the most current knowledge and advances regarding OBV receptors, endocytosis, and fusion.

The flying activity of biting midges (Ceratopogonidae: Culicoides) in Verkiai Regional Park, southeastern Lithuania

Culicoides biting midges are small dipterous insects (Diptera: Ceratopogonidae) which are known to be vectors of arboviruses, bacteria, protozoan and helminth parasites that can cause disease and mortality in livestock and poultry globally. Detailed knowledge of the Culicoides species composition and biology is essential to assess the risk of the introduction and transmission of pathogens. The aim of this study was to obtain data on Culicoides species composition and flying activity in southeastern Lithuania and to determine the meteorological variables related to the abundance of Culicoides biting midges. Biting midges were collected in Verkiai Regional Park, southeastern Lithuania, using an Onderstepoort trap once a week from April to October 2016 and 2018, and from April to July 2019; 7332 Culicoides females belonging to 22 species were identified. Both morphology and DNA barcoding were used for identification. The number of specimens trapped was highest for the Obsoletus Group, followed by Culicoides kibunensis and Culicoides impunctatus. The highest relative abundance and diversity of biting midges were found in May and June. The number of trapped biting midges correlated positively with the mean air temperature. The first biting midges in spring were caught when the mean daily temperature rose higher than 10 °C. No Culicoides were detected when the air temperature dropped below 5 °C in autumn. Wind speed and air humidity had no statistically significant effect on Culicoides abundance.

No evidence for African swine fever virus DNA in haematophagous arthropods collected at wild boar baiting sites in Estonia

African swine fever (ASF) is a highly pathogenic viral disease affecting all Suidae, with Ornithodoros moubata complex soft ticks acting as the biological arthropod vectors of the causative agent, African swine fever virus (ASFV). While ASFV is also transmissible via direct contact, pig products and fomites, other arthropods may be involved in virus transmission and persistence. Therefore, we checked various groups of blood-feeding arthropods collected during summer 2017 in wild boar habitats on the Estonian Island of Saaremaa for the presence of ASFV. Saaremaa had the highest ASF infection prevalences in Estonia in 2017, with an incidence of 9% among hunted wild boar. In addition to ASFV, we tested for other selected pathogens. In total, 784 ticks, 6,274 culicoid biting midges, 77 tabanids and 757 mosquitoes were tested as individuals or pools. No ASFV-DNA was found in any of them although about 20% of the tick samples tested positive for swine DNA. By contrast, tick-borne encephalitis virus-RNA was detected in one out of 37 tick pools (2.7%) and Borrelia burgdorferi s.l.-DNA in 20 individual ticks and 17 tick pools (25.2% of all samples). No Schmallenberg virus was detected in the Culicoides specimens. In conclusion, we found no evidence for Ixodes ricinus ticks, Culicoides punctatus and Obsoletus complex biting midges, Aedes spp., Anopheles spp. and Culiseta annulata mosquitoes, and Haematopota pluvialis tabanids playing a role in ASFV transmission in the wild boar population in Estonia.