Medical and Veterinary Entomology最新文献

Aedes aegypti L. and Aedes albopictus Skuse mosquitoes (Diptera: Culicidae), the principal vectors of many human arboviral diseases, lay eggs and undergo preimaginal development in fresh water. They have recently been shown to also develop in brackish water in coastal areas. Previous findings showed that Ae. aegypti larvae developing in brackish water possessed thicker cuticles and greater larvicide resistance than larvae developing in fresh water. The present study compared cuticle ultrastructure, resistance to adulticides, and the activities of adulticide detoxifying enzymes in female mosquitoes emerging from fresh and brackish water-developing Ae. aegypti preimaginal stages. The results showed that brackish water-derived females possessed significantly thicker tarsal and abdominal cuticles compared to fresh water-derived females. Brackish water-derived Ae. aegypti females were also significantly more resistant to three different types of pyrethroids and malathion compared to fresh water-derived females. Corresponding reversal of cuticle changes and adulticide resistance when preimaginal salinity was reversed showed that preimaginal salinity determined both procuticle structure and adulticide resistance in brackish water-derived females. Compared with fresh water-derived Ae. aegypti females, brackish water-derived females had similar activities of the adulticide-detoxifying enzyme families of esterases and glutathione S-transferases and a modest increase in the activity of monooxygenases, all of which were lower than the threshold values attributed to resistance in field populations of Ae. aegypti. Reduced permeability of the thicker and remodelled cuticles in brackish water-derived Ae. aegypti females to adulticides is proposed to be mainly responsible for their greater resistance to different types of adulticides. Greater salinity tolerance of preimaginal stages, adult cuticle changes and higher larvicide and adulticide resistance are inherited properties of brackish water-developing Ae. aegypti that reverse in a few generations after transfer to fresh water. This is compatible with a role for epigenetic changes in the adaptation of Ae. aegypti to brackish water. Greater resistance of salinity-tolerant Ae. aegypti to adulticides and larvicides poses a hitherto unappreciated problem for controlling arboviral diseases, with attendant implications also for other mosquito-borne diseases.

Blood meal patterns of mosquitoes (Diptera: Culicidae) are strongly influenced by host availability. However, the role of community composition and abundance of vertebrate hosts in determining such patterns is still unclear. Here, we analysed the blood meal sources of field-collected mosquitoes in settings with a permanent overabundance of a specific vertebrate species. Mosquitoes were collected using a battery-powered handheld aspirator every 2 months between November 2021 and April 2022 in temperate Argentina. Blood-engorged mosquitoes were collected at 11 sites corresponding to five types of settings: two cattle fields, one rabbit breeding farm, three chicken farms, two dog boarding facilities, and three geriatric hospitals, characterised by the permanent overabundance of cows, rabbits, chickens, dogs, and humans, respectively. Blood meal analysis was performed via polymerase chain reaction (PCR) and sequencing. A principal component analysis (PCA) was performed in which variables were pairs comprising an engorged mosquito species and the host species it fed on. A total of 242 blood meals from Aedes (3 species), Culex (4), Isostomyia (1) and Psorophora (1) were identified. Among these, five mammals and 12 avian species were identified as hosts. Overall, 79% of the blood meals were taken from the overabundant host, ranging from 67% to 99% in all settings except for geriatric hospitals (7%). The proportion of feeds taken on the overabundant host was lowest for Culex quinquefasciatus Say (0.67, N = 119), Cx. pipiens molestus Forskal (0.5, N = 18) and the hybrid between the two (0.5, N = 2), and highest for Aedes aegypti Linnaeus (1, N = 2), Ae. albifasciatus Macquart (1, N = 3), Ae. crinifer Theobald (1, N = 46), Cx. eduardoi Casal & García (0.9, N = 10), Isostomyia paranensis Brèthes (1, N = 20) and Psorophora ferox Humboldt (1, N = 21). By fixing host abundance in preselected settings, we propose a field design that overcomes the difficulties of estimating host community composition. This approach aids in achieving a clearer understanding of mosquito feeding patterns and their implications for arbovirus disease transmission.

Many ectoparasite species serve as vectors for bacteria that are significant to both public and animal health, with wild, domestic and synanthropic mammals acting as reservoirs. However, limited information exists on the circulation and incidence of these vectors in Argentina. We examined the diversity, prevalence and abundance of ectoparasites, along with the presence of Rickettsia spp., of Didelphis albiventris Lund (Didelphimorphia, Didelphidae) within a rural landscape of the Pampas region, Argentina. We also analysed variations in ectoparasite populations concerning seasonality, livestock farm type and farmers' management practices. Seven species of hematophagous ectoparasites were collected, including mites (Mesostigmata, Laelapidae: Laelaps echidninus Berlese); ticks (Ixodida, Ixodidae: Ixodes loricatus Neumann); fleas (Siphonaptera, Rhopalopsyllidae: Polygenis platensis Jordan and Rothschild and Polygenis rimatus Jordan); Stephanocircidae: Craneopsylla minerva wolffhuegeli (Rothschild, Pulicidae: Ctenocephalides felis Bouché); and lice (Phthiraptera, Polyplacidae: Polyplax spinulosa Burmeister). Additionally, two bacteria were detected: Rickettsia felis Bouyer et al. (Rickettsiales, Rickettsiaceae) and Rickettsia sp. (Rickettsiales, Rickettsiaceae) were closely related to Rickettsia bellii Philip et al. (Rickettsiales, Rickettsiaceae). Fleas were the most prevalent and abundant group, with C. felis showing the highest values of mean abundance and prevalence. Parasitological comparisons between dairy farms and feedlots revealed similar results, with comparable densities of D. albiventris in both farm types. Ectoparasite abundance varied seasonally, peaking during the colder season. Regression analysis indicated higher ectoparasite infestation levels on farms with more dogs. The detection of pathogenic bacteria, coupled with the high prevalence and abundance of vectors, such as C. felis, suggests a significant epidemiological risk in the region. The commensal behaviour of D. albiventris facilitates it to thrive in areas modified by anthropogenic activity, positioning this species as a potential nexus between wild and domestic epidemiological cycles of parasites and emerging pathogens. Therefore, our findings suggest that D. albiventris plays a key role in the transmission and maintenance of ectoparasites and ectoparasite-borne bacteria within these ecosystems.

Changes in climate may cause changes in the ranges, phenology and interactions of insects with other species and lead parasites to switch host species. A study of louse (flat) flies in the United Kingdom, Republic of Ireland and Isle of Man, in which licensed bird ringers acting as citizen scientists collected ectoparasites that left birds during ringing, showed recent range shifts of several species. The Common or Bird Louse Fly Ornithomya avicularia (Linnaeus, 1758), a vector of Haemoproteus sp. and trypanosomes, has undergone a major northwards range expansion of over 300 km in the United Kingdom (UK) since the 1960s. The Finch Louse Fly Ornithomya fringillina (Curtis, 1836) has also expanded its range over 300 km northwards and 400 km westwards into the Island of Ireland, and the Swallow Louse Fly Ornithomya biloba (Dufour, 1827) is now established in Wales and Southern England. The Grouse Louse Fly Ornithomya chloropus (Bergroth, 1901) has undergone a range contraction at lower altitudes and on the southern edge of its range. Other species of louse fly were detected: Crataerina pallida (Latreille, 1812), Stenepteryx hirundinis (Linnaeus, 1758), Pseudolynchia garzettae (Rondani, 1879) and Icosta minor (Bigot, 1858). Some generalist species have shifted their phenology, whereas the more specialist nest parasites of migrant birds have not, as the arrival and breeding dates of their hosts have not changed. The range changes of the generalist species of these ectoparasites may have implications for bird health, especially if they switch to new host species as their ranges shift.

Aedes aegypti, the primary vector of several medically significant arboviruses—including dengue fever, yellow fever, chikungunya and Zika—was successfully eradicated from Egypt in 1963. However, since 2011, there have been increasing reports of its re-emergence, alongside dengue outbreaks in southern Egyptian governorates, raising significant public health concerns. This study aimed to model the current and future distribution of Ae. aegypti in Egypt. Local occurrence data were integrated with bioclimatic, anthropogenic and biological environmental variables to identify key factors influencing the distribution of Ae. aegypti. Maximum entropy (MaxEnt) modelling demonstrated strong predictive performance (area under the receiver operating characteristic curve [AUC] mean = 0.975; true skill statistic [TSS] mean = 0.789). The key determinants of habitat suitability were identified as human population density, annual precipitation and the normalised difference vegetation index (NDVI). Current predictions indicate that suitable habitats for Ae. aegypti are concentrated in the Nile Valley, Nile Delta, Fayoum Basin, Red Sea coast and South Sinai. Projections under future climate change scenarios suggest an expansion of suitable habitats, particularly in the Nile Delta region. By 2050, the model predicts a 61%–68% increase in suitable habitat area, with a further 64%–69% increase by 2070, depending on the future climate scenarios. These findings are crucial for informing vector control and disease prevention strategies, particularly considering Egypt's status as one of the world's leading tourist destinations.

Culicoides oxystoma Kieffer (Diptera: Ceratopogonidae) transmits many pathogens, including seven viruses, four protozoa and one nematode. This species has a wide distribution range across northern Afro-tropical, Palearctic, Australian, Indo-Malayan realms with a broad host spectrum, including cattle, buffaloes, sheep, pigs, dogs, horses and even humans. The heterogeneous nature of Culicoides' blood-feeding patterns is well documented, but the influence of various host blood meal sources on gut bacterial composition remains scant. Adult midges were collected during April (2023) by operating UV light traps in cattle, buffalo sheds and poultry farm in Purulia (India). Besides C. oxystoma, eleven Culicoides species were collected across the sheds and farm, seven of which are vectors. Culicoides liui Wirth and Hubert and C. thurmanae Wirth and Hubert are reported from India for the first time. In all the sheds, engorged females of C. oxystoma were ubiquitous. Identification of culturable gut bacteria and the host blood meal of C. oxystoma were done through the polymerase chain reaction (PCR)-based method. Blood meal analysis confirmed the following hosts: cattle, buffaloes and humans. Identification of blood meal of engorged C. oxystoma caught from poultry farm showed positive results for humans but not for birds. Among bacteria, Bacillus cereus was abundant in all of the engorged females. Bacillus paramycoides and Enterococcus faecium were identified from females feeding on cattle and buffaloes' blood, while Alcaligenes faecalis was found in the gut contents of females that fed on cattle and human blood. The gut bacteria Alcaligenes faecalis exhibited alpha haemolytic activity. In contrast, Bacillus sp., B. cereus, B. flexus, B. licheniformis, B. thuringiensis, B. paramycoides, E. faecium, Paenibacillus sp. and Pseudomonas sp. exhibited beta haemolysis. This is the first report on the composition of gut bacteria, with particular emphasis on the haemolytic bacteria of C. oxystoma with different host blood meals. The pathogenic bacteria B. cereus, B. licheniformis and A. faecalis within the females could potentially impact pathogen acquisition and increase the probability of their zoonotic transmissibility.

We investigated the mosquito community along 315 km of the Murray River, where we identified three assemblages (upper, middle, and lower river) that exhibited different patterns of species richness and diversity over 20 years. In the lower reaches (i.e., more southern latitudes), species richness and community diversity declined over time, while there was no significant change in either the middle or upper reaches. While the overall mean abundance of the common, pathogen-carrying mosquito (Diptera: Culicidae) species Aedes camptorhynchus Thomson, increased in the lower river but declined in the upper river. These results provide important information on the diversity and abundance of mosquito communities adjacent to the Murray River and highlight the importance of considering spatial and temporal variation when assessing the risk of mosquito-borne diseases. Furthermore, data presented here illustrate that there the common public narrative around increasing mosquito abundance and geographic expansion under climate change is not universally true.

Dermacentor variabilis (Say) (Acari: Ixodidae) is a vector for pathogens that can impact human and animal health. The geographic range of this species is expanding, but there are some areas with limited up-to-date information on the distribution of D. variabilis. Therefore, the objective of this study was to describe the spatial and temporal patterns of adult D. variabilis activity in central and eastern Canada. Ticks were collected from companion animals by veterinary clinic staff. Suspected locations of tick acquisition were spatially projected, and a spatial scan statistic was used to identify statistically significant clusters of frequent submissions from veterinary clinics. Submissions were categorised by calendar week to evaluate temporal trends. In total, 1198 adult D. variabilis, one nymphal D. variabilis and one Dermacentor albipictus (Packard) were collected from the provinces of Manitoba, Ontario, Quebec, New Brunswick, Nova Scotia and Prince Edward Island from April 2019 through March 2020. Peaks in adult D. variabilis submissions occurred in May and June. Most of the submissions were received from south-eastern Manitoba, eastern Ontario and central and western Nova Scotia. A statistically significant cluster of frequent submissions that included seven veterinary clinics was identified in Nova Scotia. These findings can be used to determine the locations and times at which humans and their companion animals should be considered at an increased risk of exposure to D. variabilis and the pathogens they carry.

Mass ivermectin (IVM) treatment of livestock (MITL) is under consideration as a malaria control tool as IVM-treated livestock are lethal to blood-feeding Anopheles mosquitoes. MITL is routinely used as a prophylaxis in livestock to reduce the burden and transmission of helminth infections. Recently, there has been a shift in the veterinary IVM market in Southeast Asia wherein nearly all standard IVM formulations are now co-formulated with clorsulon (CLO). CLO is used to treat the trematode liver fluke, Fasciola hepatica. Thus, the co-administration of IVM and CLO simultaneously targets multiple livestock infections. Additionally, F. hepatica frequently afflicts human populations in endemic areas, making control of F. hepatica in livestock beneficial for One Health. CLO interrupts glycolysis in F. hepatica, but its potential effect against Anopheles mosquitoes has never been evaluated. Anopheles dirus mosquitoes were blood-fed CLO across a range of concentrations (1–10,000 nM; 0.38–3807 ng/mL), and mosquito survival was monitored for 10 days. Co-feeding experiments were also performed with An. dirus blood-fed on IVM at two concentrations (4 and 6 ng/mL) without and with CLO corresponding to peak concentration in cattle (C_max) (2700 ng/mL) and five times the C_max (13,500 ng/mL), and mosquito survival was monitored for 10 days. CLO had no mosquito-lethal effect on An. dirus. The IVM and CLO co-feed experiment did not indicate any altered effect of IVM on mosquito survival when co-fed with CLO. IVM-CLO livestock co-formulations would not likely alter the Anopheles mosquito-lethal effect of MITL. The use of MITL-CLO for malaria control would have health benefits for livestock, treating helminth and liver fluke infections, and additional One Health benefits by reducing transmission risk of liver flukes to humans.