Parasites & Vectors最新文献

Background: Phlebotomus mascittii is one of the most widespread but least studied sand fly species in Europe, occurring from Mediterranean to Central European regions. Despite its broad distribution, its potential role in Leishmania transmission remains unknown, mainly due to the lack of laboratory colonies. This study provides the first experimental assessment of the vector competence of P. mascittii for Leishmania infantum and Leishmania martiniquensis.

Methods: Wild-caught P. mascittii females from Styria, Austria, were experimentally infected using membrane feeding with blood containing L. infantum and L. martiniquensis isolates of different geographical origins. Infections were evaluated 7 days post-blood meal (PBM) by microscopy and polymerase chain reaction (PCR). Morphological forms of L. infantum were quantified and compared with infections in Phlebotomus perniciosus, a known competent vector.

Results: Fifteen (94% of dissected) P. mascittii females developed L. infantum infections, all showing colonization of the stomodeal valve, whereas L. martiniquensis failed to establish infection. Infection patterns and parasite localization closely resembled those in P. perniciosus. Morphometric analysis revealed a significantly higher proportion of metacyclic and leptomonad forms and fewer nectomonads in P. mascittii than in P. perniciosus.

Conclusions: Our findings demonstrate that P. mascittii supports full development of L. infantum to the transmissible metacyclic stage and colonization of the stomodeal valve, confirming its potential vector competence. This study provides the first experimental evidence on P. mascittii vectorial competence and highlights its epidemiological relevance in Europe.

Background: The Tibetan fox (Vulpes ferrilata) is a crucial wild definitive host of Echinococcus cestodes on the Tibetan Plateau. Fecal detection of Echinococcus DNA (fecal prevalence) is commonly used to estimate Echinococcus spp. prevalence in canine populations (population prevalence). However, this approach may be biased without individual identification, when the same individuals are repeatedly sampled, potentially leading to the misestimation of exact population prevalence.

Methods: Fecal samples collected from Tibetan foxes in Shiqu County (2010-2012) were genotyped to identify individual foxes, followed by copro-PCR to determine the population prevalence of Echinococcus spp. in the genotyped foxes. A virtual resampling program was developed to assess sampling bias and determine the optimal interval between sampling line transects. The derived optimal interval was then applied in surveillance conducted in 2015, 2016, and 2019.

Results: In total, 679 Tibetan fox feces were confirmed from 1219 field-collected samples (2010-2019). From 250 samples (2010-2012), 61 distinct fox individuals were identified. Virtual resampling analysis determined the optimal sampling interval to be 200-900 m, confirming fecal prevalence as an unbiased estimator of population prevalence. The implementation of a 500 m sampling interval in the surveillance of Echinococcus spp. (2010-2019) revealed an overall prevalence of 45.7% (95% CI 41.4-50.0%), with 32.3% (28.4-36.2%) for Echinococcus multilocularis and 23.5% (19.8-27.2%) for Echinococcus shiquicus. Mixed infections were detected annually, with an overall prevalence of 11.1% (8.4-13.8%). Significant temporal reductions were observed in the prevalence of E. multilocularis (Z = - 4.640, P < 0.001), mixed infections (Z = - 3.896, P < 0.001), and overall Echinococcus spp. (Z = - 2.155, P = 0.031). The prevalence trends of E. multilocularis and E. shiquicus were significantly associated, showing an inverse relationship (χ² = 68.861, P < 0.001).

Conclusions: A 200-900 m interval between feces sampling line transects was established as the optimal distance for assessing the prevalence of Echinococcus spp. in the Tibetan fox population. The persistent high prevalence of Echinococcus spp. in the Tibetan fox indicates an ongoing sylvatic transmission risk in Shiqu County. The opposing prevalence trends between E. multilocularis and E. shiquicus indicated a complex interaction within their shared host, warranting further study.

Background: Avian haemosporidians are single-celled eukaryotic parasites of vertebrates that require dipteran vectors for transmission. The genera Plasmodium, Haemoproteus and Leucocytozoon currently comprise over 5000 parasite lineages based on a 478-bp section of the mitochondrial cytochrome b gene, which is the standard DNA barcode for avian haemosporidians. The mitochondrial genomes of apicomplexan parasites are highly condensed, with a length of approximately 6000 bp, containing three coding genes (cytochrome c oxidase subunit I, cytochrome c oxidase subunit III and cytochrome b) and dispersed fragments of the small and large ribosomal RNA (rRNA) genes. Since the mitochondrial genomes are relatively conserved, they are valuable markers for studying the phylogenetic relationships between haemosporidian parasites. However, until recently, mitochondrial genomes were unavailable for parasites of the Haemoproteus nisi and Leucocytozoon toddi species groups, which are exclusive to accipitriform raptors and strongly diverged from other Haemoproteus and Leucocytozoon parasites.

Methods: We screened 171 accipitriform raptors from Austria and Germany using new primers targeting the cytochrome b gene of a previously neglected L. toddi clade. We also developed a new primer assay that enables the amplification and sequencing of the complete mitochondrial genomes of haemosporidian parasites. This process involved long-range PCRs with lineage-specific primers placed within the cytochrome b gene, followed by five nested PCRs targeting conserved sequence regions.

Results: Screening the accipitriform raptors revealed 10 new L. toddi group lineages. We sequenced 18 mitochondrial genomes belonging to five H. nisi group, nine L. toddi group, and two other Leucocytozoon lineages. Phylogenetic analyses based on mt genome sequences placed the L. toddi lineages within the genus Leucocytozoon, but the results did not support a monophyly of the genus Haemoproteus.

Conclusions: The new nested PCR approach with lineage-specific primers used for the long-range PCRs described herein successfully enabled the sequencing of the complete mitochondrial genomes, even in samples with mixed infections. The mitochondrial genomes of the H. nisi and L. toddi group lineages are highly valuable for resolving the phylogenetic relationships of the order Haemosporida since these parasites belong to clades distinct from other Haemoproteus and Leucocytozoon parasites.

Background: Onchocerciasis is a filarial neglected tropical disease targeted by the World Health Organization for elimination (interruption) of transmission (EOT), principally by mass drug administration (MDA) with ivermectin. Variable effectiveness and success of MDA, among other factors, has led to a markedly heterogeneous contemporary spatial landscape of endemicity and transmission, with some foci having achieved or nearing EOT, while in others, transmission persists despite decades of MDA or has only recently been identified. Communities reaching EOT or free from infection are thus vulnerable to re-introduction of infection imported by immigrants from areas with ongoing transmission.

Methods: We use the stochastic, individual-based EPIONCHO-IBM transmission model to quantify the risk of transmission persistence resulting from importation events and characterise the dynamics of ensuing onchocerciasis outbreaks in terms of microfilarial prevalence (in all ages) and anti-Ov16 seroprevalence (in children aged 5-9 years) in infection-free communities with local populations of black fly vectors.

Results: We show how the vulnerability of infection-free communities depends on their population size, the local annual biting rate (ABR, number bites/person/year) and the magnitude of importation events, defined by the number of immigrants arriving in the community and their worm burden. We show that small communities with modest ABRs are particularly vulnerable to transmission persistence following importation, with risk exacerbated by the magnitude of infection importation. We illustrate that onchocerciasis outbreak dynamics can be protracted, with seroprevalence in children often taking substantially longer than the currently recommended 3-5 years of post-treatment surveillance (PTS) to exceed 5%.

Conclusions: Our findings highlight the vulnerability of infection-free communities to introduction/re-introduction of infection and suggest that proposed PTS durations may need to be extended and complemented with additional surveillance activities and migration studies to detect and respond robustly to nascent outbreaks and sustain elimination.

Background: The biting and resting behaviours of Anopheles species, which are human malaria vectors, are specifically linked to ecological and climatic requirements that characterize certain geographical settings, such as forests and humid savannah areas where favourable conditions for malaria mosquitoes are found. In southern Senegal, the outdoor resting behaviour of Anopheles gambiae s.l. populations is suspected to be a major problem in malaria control, given that indoor-based control tools are currently deployed across the country. A longitudinal study was conducted to investigate the population dynamics, trophic preferences and resting behaviours of Anopheles gambiae s.l. in mainland and island areas in south-western Senegal.

Methods: Indoor and outdoor resting mosquitoes were collected from September 2020 to November 2021 using Pyrethrum Spray Catches and Prokopack aspirators, respectively. Field-collected mosquitoes were morphologically identified using conventional dichotomous keys, and in the laboratory, the mosquito blood meal source and molecular species identification were determined using enzyme-linked immunosorbent assays and polymerase chain reaction, respectively.

Results: Out of 765 Anopheles collected, 181 were from the mainland, and 584 were from the island. Anopheles gambiae s.l. was the predominant species (91.1%), with seasonal variation. The indoor resting densities did not significantly differ (P = 0.082) between the mainland (0.41 females per room) and island (4.09 females per room) areas. In mainland areas, the human blood index (HBI) was significantly greater (P = 0.035) in indoor resting females (76.2%) than in outdoor resting females (47.6%), whereas in island areas, the HBI was generally lower, with no significant difference (P = 0.51) between indoor (25.1%) and outdoor (31.1%) resting populations. Endophilic populations had greater HBIs in mainland areas than in island areas (P = 2.63 × 10^-5), whereas no significant difference was observed for exophilic populations (P = 0.13).

Conclusions: These findings provide a preliminary basic understanding of the feeding and resting behaviours of Anopheles gambiae s.l. populations in mainland and island areas for evidence-based malaria control programmes.

Background: An understanding of the traits that favour biological invasions has been considered to be an essential step in predicting which species would become successful invaders. Classical approaches test for differences between invasive versus non-invasive species and emphasize reproduction as a critical phenotype for successful establishment of an invasive species. However, cross-species comparisons underestimate intra-species differences, which may be relevant in species with complex invasion histories.

Methods: We capitalize on the well-characterized invasion history of the arboviral vector Aedes albopictus, which has resulted in genetically distinct native, old and invasive populations, and compared the reproductive capacity (fertility and fecundity), development (timing of egg hatching, oviposition patterns and egg hatching) and physiology (blood digestion and nutrient movement during oogenesis) across populations.

Results: The results show that invasive populations are larger in size compared to the Ae. albopictus reference Foshan population and have a higher reproductive output than both an old population and the reference Foshan population. The higher reproductive capacity of invasive mosquitoes has both a physiological and genetic basis, and is accompanied by hybrid vigour, albeit at varying degrees across populations.

Conclusions: These findings highlight population-level differences in reproductive traits of Ae. albopictus populations that may be associated with their invasion success.

Background: Despite Anopheles funestus s.s. being a highly competent and widespread malaria vector in Africa, its population structure remains largely understudied in many countries, including Tanzania. Herein, we examine the genetic diversity, geographic isolation, and gene flow of An. funestus populations across ten administrative regions in mainland Tanzania.

Methods: We employed 12 previously used microsatellite DNA markers to describe genetic diversity, isolation by distance, and gene flow patterns among ten An. funestus s.s. populations (n = 654) and one An. parensis population (n = 28), used as an outgroup, sampled across ten regions in mainland Tanzania.

Results: Overall, allelic richness (Na) and genetic diversity (H_S) did not differ significantly among populations. Although some loci and populations showed significant departures from Hardy-Weinberg equilibrium, the patterns were not indicative of substructuring within locations. Pairwise genetic divergence (F_ST) values indicated clear separation between An. parensis and An. funestus s.s., with values exceeding 0.2, consistent with species-level differentiation. Among An. funestus s.s. populations, the highest divergence was observed between southeastern coastal populations (Mtwara, Ruvuma, Lindi) and inland populations, with F_ST values up to 0.288. There was no evidence of isolation by distance. Instead, patterns of genetic divergence suggested connectivity across the Rift Valley and heterogeneity among southeastern populations. Neighbor-joining analysis and Bayesian genotype clustering identified three distinct population groups: (i) An. parensis (Dodoma), (ii) a genetically distinct An. funestus s.s. population from Mtwara, and (iii) a more homogeneous cluster comprising the remaining An. funestus s.s. populations. Notably, the Mtwara population appeared highly differentiated, with divergence approaching that between An. funestus s.s. and An. parensis, supporting its distinctiveness but not undermining the role of An. parensis as an outgroup.

Conclusions: Except for the Mtwara population, whose status will need to be clarified through whole-genome sequencing, moderate genetic divergence was found among An. funestus s.s. populations across Tanzania, despite geographical separation and the Rift Valley. The observed genetic structure suggests that anthropogenic gene flow may play a key role in shaping population divergence. Future studies should aim to delineate the effects of local adaptation from recent gene flow to further explore these dynamics.

Background: Haemaphysalis longicornis (Asian longhorned tick) is an invasive species now established in the Northeastern and Mid-Atlantic USA. It feeds on mammalian wildlife, livestock, birds, cats, dogs, and humans. Simparica^® and Simparica Trio^® contain sarolaner, a drug in the isoxazoline class, with activity against fleas, ticks, and mites.

Methods: Two laboratory studies were conducted using 30 dogs each, randomized into three groups (n = 10/group): placebo (Pet Tabs^®), Simparica Trio (minimum dose: 1.2 mg/kg sarolaner, 24 µg/kg moxidectin, 5 mg/kg pyrantel, as pamoate salt), and Simparica (minimum dose: 2.0 mg/kg sarolaner). Treatments were administered once orally on Day 0 according to the approved commercial dosing directions. Each dog was infested with 50 (± 5) unfed viable adult female H. longicornis on Days -2, 7, 14, 21, 30, 37, 49, and 63, and ticks were counted with removal and categorization at 48 h after treatment and each subsequent infestation. Ectoparasitic efficacy was calculated on the basis of the reduction in arithmetic mean of live and dead tick counts in each of the treated groups versus the untreated control group for every time point post infestation.

Results: Adequate challenge was demonstrated in both studies on the basis of live tick counts at each time point. For all sarolaner-treated groups, mean live counts were significantly (P ≤ 0.0005) lower than those for the placebo at all time points. For Simparica, in Study 1, the percentage reductions were 100% for all time points up to Day 39. On Days 51 and 65, the percentage reductions were 98.9% and 82.4%, respectively. In Study 2, reductions were 99.7-100% up to Day 65. For Simparica Trio, in Study 1, percentage reductions were 100% up to Day 51. On Day 65, the percentage reduction was 78.4%. In Study 2, reductions were 99.6-100% up to Day 39 and 97.6% and 94.1% on Days 51 and 65, respectively.

Conclusions: Results from these controlled studies demonstrated high efficacy (78.4-100%) of Simparica and Simparica Trio in reducing existing and subsequent infestations of H. longicornis within 48 h for up to 65 days post treatment.

Background: Aedes albopictus is a highly invasive vector for a variety of pathogens. The intensive use of insecticides has led to the widespread insecticide resistance in Ae. albopictus populations worldwide, compromising disease vector control efforts. We investigated whether the mosquito gut symbiotic bacterium Bacillus cereus reduces deltamethrin susceptibility in Ae. albopictus and elucidated the underlying mechanisms.

Methods: World Health Organization (WHO) standard tube bioassays were conducted to assess deltamethrin resistance status in both laboratory and field Ae. albopictus populations before and after oral infection with Bacillus cereus_HL4.2 (B. cereus_HL4.2). We measured enzymatic activities of three major detoxification enzyme families (cytochrome P450 monooxygenases, glutathione S-transferases [GSTs], and carboxylesterases) as metabolic markers. Transcriptomic profiling via RNA sequencing (RNA-seq) identified genes differentially expressed upon B. cereus infection, with subsequent validation by quantitative reverse-transcription PCR. In vitro assays assessed the direct deltamethrin-degrading capacity of B. cereus_HL4.2, and green fluorescent protein (GFP)-labeled bacterial strains tracked bacterial persistence and transmission through mosquito developmental stages.

Results: Oral infection with B. cereus_HL4.2 significantly increased the survival rate of laboratory-susceptible Ae. albopictus after deltamethrin exposure (from 7.6 ± 2.0% to 31.3 ± 4.3%) upon lethal insecticide exposure. B. cereus_HL4.2 infection elevated detoxification enzyme activities: cytochrome P450s increased 1.39-fold and GSTs increased 1.21-fold. Transcriptomic analysis revealed upregulation of genes related to the cAMP signaling pathway and purine metabolism following B. cereus_HL4.2 infection, while genes associated with ABC transporter and sensory signaling pathways were primarily downregulated. In vitro studies demonstrated that B. cereus_HL4.2 possesses direct deltamethrin-degrading capacity. GFP-tracking confirmed that B. cereus_HL4.2 colonizes the mosquito gut during larval development and persists through adult emergence.

Conclusions: Bacillus cereus_HL4.2 infection reduces deltamethrin susceptibility in Ae. albopictus primarily through two complementary mechanisms: (i) metabolic upregulation of detoxification enzymes and related genes, and (ii) direct enzymatic degradation of deltamethrin. Genetically modifying B. cereus_HL4.2 may offer a potential strategy for managing insecticide resistance in mosquitoes.

Background: Crimean-Congo haemorrhagic fever (CCHF) is a tick-borne disease endemic to Africa, Southern Europe, and Western Asia. Its main vectors, Hyalomma ticks, can spread to and possibly establish populations in non-endemic regions via migratory birds.

Methods: We summarized the association between migratory birds and Hyalomma ticks by analysing spatial and temporal patterns in tick prevalence and infestation intensity on migratory birds through a systematic review of studies conducted in Europe, Western Asia, and Northern Africa between 1954 and 2022.

Results: We reviewed 37 studies and retrieved data from one additional unpublished datasets. Overall, we collected data on the occurrence of 3876 ticks, most of which were in immature life stages, from 1553 individuals of 75 migratory bird species. The prevalence of ticks from both the Hyalomma genus and Hyalomma marginatum complex ticks (H. marginatum and H. rufipes) on migrating birds declined significantly with increasing latitude of the sampling sites in spring. Additionally, we found that the infestation intensity of both tick groups on migratory birds was significantly higher among intra-Palearctic migrants than in Afro-Palearctic migrants.

Conclusions: This review underscores the role of migratory bird species in spreading Hyalomma ticks across the Northern Hemisphere and highlights their potential as an early warning system for CCHF outbreaks. This study demonstrates the need to integrate migratory birds into CCHF surveillance systems as sentinels of Hyalomma tick dispersal, providing a reference framework for monitoring tick-borne risks along avian migration routes.