Parasites & Vectors最新文献

Background: Trypanosoma cruzi, the etiologic agent of Chagas disease, is transmitted via the dejections of triatomine insects such as Triatoma infestans. Parasite development inside the vector depends on temperature, which determines the extrinsic incubation period (EIP) and modulates the parasite load. As global warming is expected to increase mean temperatures and thermal variability, these shifts may influence vector competence.

Methods: Triatoma infestans individuals were experimentally infected with T. cruzi Dm28c strain and then exposed to four thermal regimes: two constant (18 °C and 27 °C) and two fluctuating (18 ± 5 °C and 27 ± 5 °C). Parasite load in the dejection samples was quantified by quantitative PCR over 42 days and the time to the first positive dejection determined to estimate the EIP.

Results: Higher temperatures significantly shortened the EIP, with mean values of 18.6 days at 18 ± 0 °C, 17.3 days at 18 ± 5 °C, 9.6 days at 27 ± 0 °C and 11.0 days at 27 ± 5 °C. Temperature variability did not affect the EIP but it did increase parasite load under cold conditions. Parasite load showed a bell-shaped curve, peaking earlier and at higher levels at warmer temperatures. A larger volume of ingested blood also reduced the EIP, especially under cold treatments.

Conclusions: Rising temperatures accelerate T. cruzi development within T. infestans, potentially enhancing vector competence under climate change scenarios. Although temperature variability did not affect the EIP, it increased parasite load, particularly under cold conditions, which is a relevant result considering that low temperatures have historically limited the vector and Chagas disease transmission. Temperature variability-not only mean warming-can modulate parasite development. Our results therefore provide novel and relevant insights into how climate change may alter vector-borne disease dynamics.

Background: Aedes aegypti is an important vector for several human-pathogenic arboviruses. RNAi is the principal antiviral immune pathway in mosquitoes. Key steps of antiviral RNAi are processing of long dsRNAs into siRNA duplexes by dicer-2; loading of the siRNA duplexes onto Argonaute-2 with the help of R2D2; RISC formation via incorporation of Argonaute-2, which contains an siRNA; RISC-mediated targeting and degradation of homologous viral RNAs. Here, we generated an r2d2 knockout mosquito line to reveal how RNAi impairment during RISC loading complex (RLC) formation would affect arbovirus infection of Ae. aegypti.

Methods: CRISPR/Cas9 gene editing has been used to knock out r2d2 in Ae. aegypti. Crossing experiments were conducted to reveal the effects of loss of r2d2 function on fecundity and fertility. Mayaro virus (Togaviridae: MAYV) infection and RNAi pathway gene expression levels were monitored using time-course RT-qPCR assays. Small RNA profiling was conducted to determine small RNA abundance in ΔR2D2^(+/-±) mosquitoes.

Results: We show that in Ae. aegypti, the r2d2 allele is linked to the sex determination locus on chromosome 1. It was not possible to generate homozygous ΔR2D2^(-/-) mosquitoes, indicating that complete loss of r2d2 function is lethal to Ae. aegypti. Our observations suggest that r2d2 function is not limited to RNAi but also affects mosquito fecundity/fertility, likely through follicle development. Monoallelic disruption of r2d2 increased the replication of MAYV, and r2d2 expression was also increased in infected mosquitoes. MAYV infection of ΔR2D2^(+/-±) mosquitoes was associated with an increase in abundance of putative vpiRNAs. However, impairment of r2d2 did not affect the function of dicer-2, as there was no difference in the 21 nt siRNA profiles between the ΔR2D2^(+/-±) mosquitoes and the non-transgenic control.

Conclusions: The RNAi pathway gene, r2d2, is an essential gene, and it is not possible to generate mosquitoes with biallelic (complete) loss of r2d2 function. Monoallelic impairment of r2d2 compromises the siRNA pathway downstream of dicer-2 function, at the point of RLC formation. In MAYV-infected mosquitoes, this defect in siRNA pathway function is compensated for by an increased piRNA pathway activity, which moderates increases in viral replication over a 10-day period.

Background: Malaria is a major public health concern and is transmitted to humans by the bite of infected Anopheles mosquitoes. One strategy to reduce populations of zoophagic Anopheles (i.e., likely to feed on other animals as well as humans) is the use of systemic veterinary parasiticides. The most widely systemic parasiticide used for this purpose is ivermectin. Ivermectin is available for livestock in two formulations; injectable and topical "pour-on." The purpose of this study was to evaluate the survival and fecundity of a zoophagic species, Anopheles stephensi, when fed on calves treated with different ivermectin formulations.

Methods: Three groups of four dairy calves were used; calves in one group received a single subcutaneous injection of commercial ivermectin, calves in another group were treated topically once with pour-on ivermectin, and the third group was left untreated. At various times after treatment, groups of mosquitoes were fed simultaneously on different parts of the body to determine if feeding location of mosquitoes influenced the efficacy of treatment. Engorged mosquitoes were maintained for 7 days to monitor survival and fecundity.

Results: Both formulations significantly reduced An. stephensi survival and fecundity for up to 9 and 14 days, respectively, following treatment of calves. Topical formulation of ivermectin applied to the back of the calves significantly reduced the survival of An. stephensi that fed on the back for up to 23 days after treatment, but not for mosquitoes that fed concurrently on the belly or the leg of the same calves, suggesting that a portion of topically applied ivermectin may remain at the site of application. Mosquitoes were less likely to feed on topically treated calves, implying that topical application may confer some mild repellency.

Conclusions: Determining the body location(s) where zoophagic Anopheles mosquitoes feed on livestock (e.g., legs) will allow targeted application and methods (e.g., foot baths) for more efficient use of topical formulations of ivermectin as part of an integrated zoophagic vector management strategy.

Background: Ixodid ticks are critical vectors of pathogens affecting human, livestock, and wildlife health. In tropical regions, landscape heterogeneity is a key driver of tick-host associations, yet comprehensive studies across diverse habitats remain limited.

Methods: This study investigated tick infestations on a wide range of animal hosts across four major habitat types comprising natural forests, oil palm plantations, rural villages, and urban areas in Peninsular Malaysia from 2022 to 2023.

Results: Of 1277 hosts of 38 families and 79 species examined, 270 (21.1%) were infested with 1985 ixodid ticks, representing 16 ixodid species. The most abundant tick species were Haemaphysalis wellingtoni (44.7%), Amblyomma cordiferum (19.7%), and H. semermis (9.6%). Network and correspondence analyses revealed distinct tick-host-habitat associations: A. cordiferum, H. semermis, H. hystricis, and Ixodes granulatus were strongly associated with natural forests, whereas H. wellingtoni predominated in oil palm plantations and rural villages on domestic and jungle fowl (Gallus gallus domesticus and Gallus gallus). Wild boar (Sus scrofa) hosted the most diverse tick species, particularly in urban and rural settings. Notably, A. varanense exhibited strict specificity to reptiles.

Conclusions: These findings demonstrate the influence of habitat on tick-host interactions, offering critical insights for targeted surveillance and integrated One Health strategies to mitigate tick-borne disease risks in rapidly changing tropical ecosystems.

Background: Bat flies are ubiquitous ectoparasites of bats, recognised as potential vectors for viral and bacterial transmission between individual bats within a roost. Despite this, little is known about the seasonal dynamics of bat flies. Here, we present the results of a longitudinal study that compares seasonal prevalence and host risk factors for bat fly (Diptera: Nycteribiidae) parasitism with that of Bartonella and Borrelia spp. detected in Pteropus alecto and P. poliocephalus in eastern Australia.

Methods: Flying foxes were sampled at nine different roosts in south-east Queensland and northern New South Wales between February 2018 and September 2022 using mist nets. Host and ectoparasite data were recorded, and bat fly specimens were collected for identification. Blood samples collected from the flying foxes were screened for the presence of Bartonella and Borrelia DNA using polymerase chain reaction (PCR).

Results: Ectoparasite data were recorded from 2235 flying foxes and 840 had blood samples screened for Bartonella and Borrelia DNA. Cyclopodia albertisii was the predominate nycteribiid species identified, with few detections of C. australis. Nycteribiid prevalence had a consistent annual cycle (ranging from 8.6% to 100%) that depended on local climatic factors, increasing with increased temperature and humidity during summer and decreasing in winter. Bartonella spp. prevalence exhibited less variation seasonally (ranging from 50% to 100%) with a peak in winter that was driven by host age, with juvenile bats having a reduced probability of infection compared with subadults and adults. Borrelia spp. were rare and showed no clear seasonality.

Conclusions: This study reports the longitudinal occurrence of the blood-borne bacteria Bartonella spp. and their likely ectoparasite vectors in Australian flying foxes. The findings contribute to knowledge of nycteribiid ecology critical for understanding their vector potential within flying fox roosts and provide direction for future research into nycteribiid-mediated transmission dynamics.

Background: Long-lasting insecticidal nets (LLINs) are crucial for malaria prevention in Cameroon, yet their operational performance may be compromised because of deterioration of the physical integrity and bioefficacy of nets. This study evaluated LLINs, physical integrity, and bioefficacy following mass distribution campaigns in two regions in Cameroon: East (Bertoua) and Centre (Eyang).

Methods: Household surveys were conducted to assess ITN ownership, usage patterns, and maintenance practices. Net condition was measured using the proportionate hole index (pHI), and bio-efficacy was assessed using WHO cone bioassays against Anopheles gambiae (s.s.) (Kisumu strain) and local field mosquitoes.

Results: A total of 55 LLINs from Bertoua and 30 from Eyang were sampled. LLIN ownership was comparable between sites (66.7% in Bertoua vs. 67.9% in Eyang), with a higher usage rate in Bertoua (73.3%) compared to 58.2% in Eyang. In Bertoua, a large percentage of LLINs (59.6%) were too torn, with Olyset Plus being the most common brand. In contrast, Eyang had a lower proportion of torn nets (44%), and households used a combination of different brands, including the Olyset net, Permanet 2.0, and Royal Sentry. Against the susceptible Kisumu strain, Bertoua's Olyset Plus nets showed optimal efficacy with a 94.6% mortality rate, exceeding the World Health Organization's (WHO) threshold of ≥ 80%. In contrast, nets from Eyang had a 79.3% mortality rate, falling short of the optimal threshold. However, when tested against local field mosquitoes, Olyset Plus (pyrethroid + PBO) showed higher efficacy (mortality rate of 31.8%) than the other brands (7.1% from Olyset net; 18.6% for Permanet 2.0; and 8.6% for Royal Sentry) (p > 0.0001).

Conclusions: These findings underscore the crucial importance of proper LLINs maintenance, particularly regarding washing practices. The results also indicate the need to deploy newer generation LLINs to address emerging insecticide resistance and strengthen malaria control efforts.

Background: Arboviruses transmitted by mosquitoes pose a global health threat, causing diseases ranging from mild fevers to severe encephalitis and hemorrhagic fevers. Despite their growing impact, arbovirus research is hindered by biosafety constraints and the need of specialized BSL-3 insectariums. To circumvent these challenges, mosquito-derived cell lines have become indispensable tools for investigating virus-vector interactions. However, most available cell lines originate from Aedes and Anopheles spp., creating a critical research gap for other key vectors such as Culex spp. Although a few cell lines were previously established, they did not represent primary transmitters of West Nile virus (WNV) and other emerging arboviruses in Europe, such as Culex pipiens.

Methods: To address this gap, the current study aimed to characterize two recently established Culex pipiens cell lines: CPE/LULS50 (Culex pipiens pipiens & molestus) and CPL/LULS56 (Culex pipiens molestus) in more detail including testing their virus susceptibility, antiviral RNAi response, and possible presence of insect-specific viruses.

Results: The replication of arboviruses from three clinically relevant families (Flaviviridae, Peribunyaviridae, and Togaviridae), as well as insect-specific viruses, was observed in both CPE/LULS50 and CPL/LULS56 cell lines. Furthermore, small RNA profiling revealed production of virus-specific small interfering RNA (siRNA) in both cell lines for all tested viruses. Interestingly, virus-specific PIWI-interacting RNA (piRNA) was only detected for the Peribunyaviridae.

Conclusions: The current study demonstrates that the CPE/LULS50 and CPL/LULS56 cell lines are suitable candidates to facilitate research into Culex-specific virus-vector interactions, ultimately contributing to mitigation of the impact of Culex-borne arboviruses on public health.

Background: Malaria mosquitoes reproduce in mating swarms. Previous studies have reported a pronounced activity peak in male mosquito swarms immediately following simulated sunset, typically lasting around 20 min. This peak represents the main swarm formation, where several mosquitoes concentrate above visual markers and maintain prolonged flight activity. However, most studies rely on laboratory setups with balanced or single-sex swarms, which do not reflect the male-biased sex ratios observed in the field.

Methods: In this study, we studied swarming behavior of male and female Anopheles coluzzii mosquitoes in five sex ratios (male-only 1:0, male-biased 3:1, balanced 1:1, female-biased 1:3, female-only 0:1) using three-dimensional infrared videography to quantify spatial structure of swarms and flight speed of individual mosquitoes. For each ratio, we analyzed changes in spatial arrangement and flight speed through time and between conditions.

Results: Swarm volume varied following a quadratic trend ( $R^2=0.889$ ). As the proportion of females in the swarm increased, the volume of the swarm increased, ranging from 305.1 cm³ in male-biased swarms to 612.6 cm³ in female-only swarms. Mean flight speed also increased with female proportion, from $0.66$  m/s (1:1 balanced ratio) to $0.87$  m/s (0:1 female-only ratio), showing a moderate relationship with volume ( $R^2=0.504$ ). Swarm density and speed were negatively correlated, indicating that mixed swarms are not only smaller in volume but also exhibit higher track densities ( $R_{\text{Spline}}^2=0.712)$ suggesting tighter, slower swarms in male-rich groups. Furthermore, we used a Random Forest as an exploratory classifier to (1) identify which kinematic features most differentiate operational sex ratio (OSR) groups and (2) test, as a proof of concept, whether sex ratio can be inferred from kinematic signatures.

Conclusions: These results demonstrate the influence of sex ratio on swarm kinematics and support the use of machine learning for behavioral classification in mosquito ecology.

Background: Aedes aegypti is typically regarded as a freshwater mosquito; however, recent studies have documented its development in brackish water habitats in coastal regions, including Sri Lanka's Jaffna Peninsula. Compared with freshwater populations, brackish water samples in Jaffna display enhanced salt tolerance throughout larval-to-adult development, along with differences in gene expression, cuticle morphology and composition, and insecticide susceptibility.

Methods: To explore the genetic basis of these differences, we performed a comparative genomic analysis using 5135 genome-wide single nucleotide polymorphisms (SNPs) from Ae. aegypti inhabiting freshwater and brackish water sites in the Jaffna Peninsula. Genetic diversity, population structure, and demographic parameters were evaluated using publicly available software. Candidate genomic regions potentially involved in salinity tolerance were identified through tests for environmental associations and genetic outlier detection.

Results: After performing genotype quality control and first-degree relative removal on the initial 121 mosquitoes genotyped, the final dataset comprised 13 freshwater and 21 brackish water individuals. Ae. aegypti populations from the Jaffna Peninsula showed limited evidence of genetic structuring by collection site, with a subtle pattern associated with larval water salinity (distance-based redundancy analysis [dbRDA] P = 0.002, adjusted R² = 0.01). Brackish-water populations displayed higher linkage disequilibrium, reduced effective population size, and lower nucleotide diversity relative to freshwater populations. Genetic outlier and environmental association analyses identified loci associated with fatty acid metabolism and other cellular pathways (e.g. Toll and Imd signaling pathways) as differentiated among the groups.

Conclusions: We found subtle genetic differentiation between freshwater and brackish-water Ae. aegypti populations from the Jaffna Peninsula, suggesting that brackish-water populations may experience distinct evolutionary pressures potentially linked to adaptation to saline environments. Analyses point to fatty acid metabolism as one of the biological processes that could contribute to salinity tolerance in Ae. aegypti, possibly influencing cuticle modifications as a physiological response. Additional studies incorporating more collection sites and larger sample sizes for each salinity group are needed to further elucidate the mechanisms driving this differentiation. The ability of Ae. aegypti to adapt to brackish water substantially expands the range of potential larval sites it can occupy, particularly in coastal areas, and emphasizes the need to adjust vector control strategies accordingly.