Parasites & Vectors最新文献

Background: Leishmaniasis is a parasitic disease transmitted by female sand flies and caused by protozoan parasites of the genus Leishmania. Accurate quantification of parasite load within vectors is essential for understanding transmission dynamics and vector competence. This study compares two quantitative polymerase chain reaction (qPCR) methods for detecting and quantifying Leishmania infantum in three experimentally infected sand fly species (Phlebotomus perniciosus, Phlebotomus argentipes, and Phlebotomus orientalis).

Methods: One method targets kinetoplast minicircle DNA, which offers high sensitivity but limited quantitative precision, while the other targets the single-copy Meta-1 gene, providing more precise quantification but reduced sensitivity in low-level infections.

Results: A positive correlation between the two molecular markers supports a combined approach to maximize both sensitivity and accuracy in surveillance and transmission studies. Following this methodological comparison, significant differences were observed in parasite proliferation among sand fly species and L. infantum strains, with Ph. orientalis confirmed as a highly competent vector for Leishmania donovani complex.

Conclusions: Together, these findings highlight that combining high-sensitivity (kinetoplast DNA [kDNA]) and single-copy (Meta-1) targets enables both accurate and sensitive quantification of Leishmania infections in sand flies, improving the assessment of parasite-vector interactions.

Background: The control of toxoplasmosis relies on conventional chemotherapeutics, which have hitherto unresolved concerns.

Methods: Swiss albino mice were intraperitoneally (IP) infected with 5 × 10³ tachyzoites of RH HXGPRT( -) strain of Toxoplasma gondii, then IP treated with one-fourth lethal dose 50 (one-fourth LD50) of Cerastes cerastes venom (CCV) for three consecutive days (LD = 0.535 mg/kg). The anti-Toxoplasma activity of CCV was evaluated, for the first time, in immunocompetent (IC) and immunosuppressed (IS) mice via estimation of their mortality and survival time, microscopical counting of peritoneal tachyzoites, measurement of liver parasite burdens using quantitative real-time polymerase chain reaction (qRT-PCR), detection of infectivity, and ultrastructural changes of the treated tachyzoites. The safety of the used dose was biochemically assessed by measuring liver, kidney, and oxidative stress markers in serum.

Results: CCV induced an insignificant reduction in mortality rate (MR) and a significant increase in survival time of mice. A statistically significant decrease in the mean peritoneal parasite burden with 89.8% and 90.8% reduction (%R) was observed in both IC and IS-treated subgroups compared with their controls, respectively. This reduction was consistent with 88% and 86% decrease in liver parasite load, respectively, and obvious ultrastructural alterations in treated tachyzoites. Concerning the infectivity study, the percent reduction was 78.8% and 85.5% in the peritoneal fluid and 71.1% and 60.4% in the liver tissues of IC and IS subgroups, respectively. The biochemical safety of the used dose and its high antioxidant activity were verified.

Conclusions: Thus, one-fourth LD50 of CCV can be considered a promising, effective natural alternative to standard chemotherapy for acute toxoplasmosis.

Background: The genetic variability of a large collection of European samples of the zoonotic pathogen Cryptosporidium parvum has been recently explored on the basis of a novel multi-locus sequence typing (MLST) scheme. In this work, we assessed the usefulness of this scheme to type C. parvum samples from Italy, a country where this pathogen is widespread and associated with human infections.

Methods: Polymerase chain reaction (PCR) and sequencing for the eight markers of the MLST scheme were performed on 31 human- and 21 animal-derived C. parvum samples. MLST data from 27 samples of animal origin previously sequenced at the genome level were also included. Sequence data for the glycoprotein 60 (gp60) gene were also generated. Phylogenetic and cluster analyses were conducted.

Results: Full genotyping data were obtained for 72 of 79 samples, and 39 different profiles were categorized, 28 of which were found in individual samples (singletons). A new allele was found at the marker on chromosome 2 in a human-derived sample. When compared with the 154 profiles previously described in Europe, 30 of the 39 profiles (76%) were found to be restricted to Italy, a result compatible with a model of isolation by distance, with geographically structured populations. Analysis of the gp60 sequences identified 19 different subtypes among the 55 samples belonging to family IIa, and 7 different subtypes among the 16 samples belonging to family IId. Phylogenetic and haplotype analyses did not identify clusters related to the host, the geographic origin (i.e., the Italian regions), or the time of collection of the samples but did identify two different populations, mirroring data obtained from whole genome comparative analyses.

Conclusions: The MLST scheme appears to be a promising method for genotyping C. parvum samples, as it provided higher discrimination compared with gp60 and enabled the recognition of the two major populations circulating in Europe and in Italy.

Background: Birds (Aves) are considered to play important roles in the dissemination of ticks and tick-borne pathogens, yet the global extent of their contribution to vector maintenance and long-distance dispersal remains poorly quantified. This study provides a comprehensive global synthesis of bird-associated ticks (BATs) and bird-associated tick-borne pathogens (BATBPs) to characterize the epidemiological roles of birds and assess the resulting public health and biosecurity risks.

Methods: We systematically searched multiple bibliographic databases and GenBank up to February 2025 in accordance with Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines. Field-based studies reporting bird-tick-pathogen associations were included. Thematic maps showing the geographical distributions of birds, BATs, and BATBPs were produced in ArcGIS, and pooled infestation prevalence was estimated via logit-transformed random-effects meta-analysis with the Hartung-Knapp adjustment.

Results: Our synthesis of 772 studies and 86 molecular records identified 185 BAT species and 102 BATBPs across 34 avian orders, representing 77.3% of all global orders. Within the BATBP spectrum, 53.9% are zoonotic, and 99 tick species have documented records of human-biting. Passeriformes (songbirds) hosted the greatest tick diversity (129 species), while Galliformes exhibited the highest pooled infestation prevalence (17.6%; n = 29 studies, m = 18,746 birds). Globally, allochthonous tick records showed relatively high spatial overlap with the Black Sea-Mediterranean and East Atlantic flyways. Critically, we identified a profound surveillance imbalance in Asia, which accounts for only 6.5% of sampling coordinates (26/397 sites) despite exhibiting a high diversity of emerging pathogens.

Conclusions: Birds serve as important contributors to global tick-borne disease epidemiology through local vector maintenance and intercontinental bio-dispersal. They support tick feeding and life-cycle completion and may disperse ticks during migration, facilitating population establishment in new areas. Molecular evidence indicates that birds carry a broad spectrum of tick-borne pathogens; however, the available evidence is largely observational, and experimental validation is required to clarify reservoir competence and transmission. Strengthening integrated One Health surveillance of high-risk hubs, particularly in data-deficient regions such as Asia, is essential to mitigate spillover risk at shifting ecological and migratory interfaces.

Purpose: Anopheles stephensi, a malaria vector in South Asia and parts of the Middle East, has been detected as an invasive species in numerous African countries in recent years. It threatens to increase malaria disease burden and reverse gains made in malaria control and elimination. To halt further expansion, it is critical to understand the biological characteristics that may have facilitated An. stephensi range expansion. In its invasive range, An. stephensi larvae have been found to colonizea rtificial containers, many of which are shared with Aedes aegypti. The success of Ae. aegypti as an invasive vector is often attributed to the use of artificial containers and the ability of Ae. aegypti eggs toremain viable in the absence of water for months. While An. stephensi is found in artificial containers, itis unclear whether the eggs can remain viable without water for extended periods.

Methods: In this study, we used two laboratory strains of An. stephensi (SDA500 and STE2)and one Ae. aegypti strain (LVP-IB12) to evaluate 1) whether An. stephensi eggs can remainviable like Ae. aegypti when egg substrates are completely dried and 2) assess egg viabilityduration at varying temperatures when eggs are held on a moistened substrate in a highhumidity environment.

Results: An. stephensi egg viability and subsequent larval survival was observed consistently when moistened egg sheets were held at 15˚C in a high humidity environment forup to 14 days in both strains. An. stephensi eggs were not viable when completely dried, exceptwhen the protocol was amended to include a 15°C storage temperature. Though egg viability and larval survival was observed in the amended protocol for SDA500 and STE2 (16% and 21% respectively), it was significantly less than that of LVP-IB12 (83%) and was only observed in the eggs stored for the shortest timepoint.

Conclusions: These fi ndings suggest that An. stephensi may remain viable if eggs are transported underideal conditions (15˚C and >75% RH) through trade routes. Thus, the persistence of An. stephensi eggs inthe absence of water should be considered in programs that engage in surveillance and control of An. stephensi in Africa.

Background: Phlebotomus perniciosus is the primary vector of Leishmania infantum in Spain, occurring in both continental and insular regions. This study investigates the genetic structure of P. perniciosus populations from Majorca (island) and Barcelona (mainland), two geographically close but ecologically distinct regions in the western Mediterranean.

Methods: Mitochondrial cytochrome c oxidase subunit I (COI) gene sequences were analyzed from 167 P. perniciosus specimens, including 100 morphologically identified field-collected specimens from Majorca and Barcelona, supplemented with reference data from the South and West Iberian Peninsula and North Africa. Population differentiation was assessed using genetic diversity indices, Bayesian phylogenetic inference, analysis of molecular variance (AMOVA), pairwise Fst values and Nm estimates, haplotype networks, and a Mantel test.

Results: Phylogenetic analysis confirmed the morphological identification of all P. perniciosus specimens, grouping them into a single clade, with distinct subclades corresponding to the geographical origin. Haplotype analysis revealed 56 genetic variants, with the predominant haplotype represented by 37 specimens in Majorca and 40 in Barcelona. Significant genetic differentiation was observed between populations from Majorca and Barcelona (Fst = 0.78262, P < 0.00001), indicating limited gene flow. Nucleotide diversity was higher in Majorca (π ± SD = 0.0037 ± 0.00090) than in Barcelona (π ± SD = 0.0006 ± 0.00021). Majorcan specimens showed close genetic affinity to the Algerian and Tunisian populations (Fst = 0.02470, P > 0.05), while Barcelona specimens were more closely related to those of the South and West Iberian Peninsula (Fst = 0.51225, P < 0.00001).

Conclusions: These findings indicate that geographic isolation and historical dispersal may have shaped the P. perniciosus genetic structure. The Balearic Sea appears to act as a significant barrier, restricting gene flow between island and Iberian mainland populations. The study supports the utility of COI in phylogeographic research and demonstrates how island-mainland comparisons can help reveal evolutionary processes in vector species.

Background: Insecticide resistance monitoring in vector populations is a key pillar of the Global Plan for Insecticide Resistance Management in malaria vectors. This study assessed the susceptibility of Anopheles arabiensis populations from Mwea and Ahero, Kenya to six insecticides. The association between insecticide resistance and Microsporidia MB infection, a symbiont known to block malaria transmission in An. arabiensis was also investigated.

Methods: Mosquitoes were exposed to permethrin, deltamethrin, alphacypermethrin, malathion, bendiocarb, and dichlorodiphenyltrichloroethane (DDT) using the Centers for Disease Control and Prevention (CDC) bottle bioassay. Resistance intensity and synergist bioassays for pyrethroids were conducted to evaluate the strength of resistance and the contribution of cytochrome P450s to pyrethroid resistance. Microsporidia MB infection was detected and quantified using qPCR.

Results: A total of 3120 females were tested. Populations from both study sites were susceptible to bendiocarb but resistant to all three pyrethroids. Mortality rates following exposure to alpha-cypermethrin, permethrin, and deltamethrin respectively were 0%, 4.7%, and 25.7% in Ahero, and 25.7%, 6.2%, and 26.6% in Mwea. Mortality increased with increasing permethrin concentration with 1 × , 2 × , 5 × , and 10 × values of 4.7%, 17.2%, 70.8%, and 84.4% respectively in Ahero and 6.2%, 29.4%, 85.3%, and 100% in Mwea. The Ahero population was susceptible to malathion but had reduced susceptibility to DDT (92.7%) while the Mwea population was susceptible to DDT and resistant to malathion (69.2%). Pre-exposure to piperonyl butoxide fully restored pyrethroid susceptibility in the Mwea population, indicating metabolic resistance and partially restored permethrin susceptibility (4.7 to 86.7%) in Ahero population, indicating the presence of other resistance mechanisms. Microsporidia MB was detected in Ahero population and mean (± se) infection density was significantly higher in mosquitoes that survived 2 × and 5 × permethrin doses (1017.6 ± 296.6) compared with those that succumbed to these doses (171.3 ± 78.0).

Conclusions: Anopheles arabiensis populations from the two sites exhibit heterogeneous yet high levels of insecticide resistance, particularly to pyrethroids. The findings highlight the need to incorporate synergist-based interventions into resistance management strategies. This study is the first to document an association between Microsporidia MB density and the intensity of insecticide resistance in An. arabiensis, and further studies are needed to clarify this relationship and its significance to malaria control.

Background: Ivermectin is an emerging vector control; however, its toxicity against insecticide-resistant mosquito populations with multiple resistance mechanisms remains unclear. This study investigated the toxic effects of ivermectin on three multiple insecticide-resistant mosquito populations from Ghana.

Methods: Susceptibility to different insecticides, target-site mutations associated with insecticide resistance, and metabolic resistance mechanisms were determined among field mosquito populations of Anopheles gambiae sensu lato, Aedes aegypti, Culex species, and susceptible Anopheles gambiae sensu stricto Kisumu (laboratory strain). Dose-response bioassays were performed by feeding the mosquito populations with different concentrations of ivermectin dissolved in a 10% sugar solution. Mortality was recorded post-feeding every 12 h for 48 h.

Results: The field mosquito populations were resistant to most of the insecticides tested, particularly the pyrethroids. Different kdr mutations and metabolic resistance mechanisms were detected in the field populations. The susceptible An. gambiae s.s. Kisumu strain had a significantly higher hazard of death compared with the insecticide-resistant An. gambiae s.l. (exhibiting kdr, Ace-1 mutations and metabolic resistance mechanisms), across all the ivermectin concentrations (P ≤ 0.001). Furthermore, the lethal doses of ivermectin that killed 95% wild An. gambiae s.l. and Culex spp. (permethrin, deltamethrin, and dichloro-diphenyl-trichloroethane [DDT] resistant) were comparable, but lower than the dosage that killed 95% wild Ae. aegypti with F1534C, V410L, and V1016I mutations and metabolic resistance mechanisms.

Conclusions: The study showed that the multiple insecticide-resistant An. gambiae s.l. population was more tolerant to ivermectin compared with the susceptible strain, but more susceptible to the drug compared with Ae. aegypti. These findings suggest heterogeneity in ivermectin responses across the mosquito species and resistant phenotypes, and therefore, further studies are needed to identify the mechanisms underlying these differences and to assess their relevance under broader epidemiological and ecological contexts.

Background: The northern fowl mite (NFM), Ornithonyssus sylviarum, is one of the most important external parasites of commercial poultry in the USA. NFM feeds on blood, causing irritation and stress to infested birds and potentially reducing egg production in flocks with high levels of mite infestation. Fluralaner is a systemically active insecticide and acaricide. We report on two studies that evaluated the efficacy of fluralaner administered to layer chickens in medicated drinking water through two single doses of 0.5 mg fluralaner per kg chicken body weight at 7 days apart for control of NFM.

Methods: In two separate studies, white Leghorn chickens (Gallus gallus domesticus) were exposed to NFM so that they developed mite infestations. The first study was a dose confirmation study (n = 64 pullet birds per treatment group). The second study was a field efficacy study (n = 400 layer birds per treatment group). Once infested with NFM, birds were assigned to Medicated or Control treatment groups. In the Medicated group, a fluralaner solution was administered through medicated drinking water on study day 0 and again on day 7. The Control group received only unmedicated drinking water. NFM present in the vent region of birds were recorded prior to treatment (day -7 for dose confirmation and day -5 for field efficacy studies) and post-treatment on days 2, 8, 14, 19, and 28. In each study, product efficacy was determined by comparison of mite counts on Medicated and Control birds.

Results: The number of mites was significantly reduced on Medicated group birds relative to Control group birds by day 2. At day 2 post-treatment, 99% control efficacy (> 99% for geometric mean) was achieved in the dose confirmation study and > 96% (> 99% for geometric mean) control efficacy was achieved in the field efficacy trial. Control efficacy in both studies exceeded 99% from day 8 to day 28. There were no adverse health impacts observed in birds treated with fluralaner.

Conclusions: This study confirms the effectiveness of fluralaner for control of NFM when administered to chickens through drinking water as two single doses of 0.5 mg/kg chicken body weight at 7 days apart.

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.