Semi-field assessment of the BG-Malaria trap for monitoring the African malaria vector, Anopheles arabiensis

Odour-baited technologies are increasingly considered for effective monitoring of mosquito populations and for the evaluation of vector control interventions. The BG-Malaria trap (BGM), which is an upside-down variant of the widely used BG-Sentinel trap (BGS), has been demonstrated to be effective to sample the Brazilian malaria vector, Anopheles darlingi. We evaluated the BGM as an improved method for sampling the African malaria vectors, Anopheles arabiensis. Experiments were conducted inside a large semi-field cage to compare trapping efficiencies of BGM and BGS traps, both baited with the synthetic attractant, Ifakara blend, supplemented with CO2. We then compared BGMs baited with either of four synthetic mosquito lures, Ifakara blend, Mbita blend, BG-lure or CO2, and an unbaited BGM. Lastly, we compared BGMs baited with the Ifakara blend dispensed via either nylon strips, BG cartridges (attractant-infused microcapsules encased in cylindrical plastic cartridge) or BG sachets (attractant-infused microcapsules encased in plastic sachets). All tests were conducted between 6P.M. and 7A.M., with 200–600 laboratory-reared An. arabiensis released nightly in the test chamber. The median number of An. arabiensis caught by the BGM per night was 83, IQR:(73.5–97.75), demonstrating clear superiority over BGS (median catch = 32.5 (25.25–37.5)). Compared to unbaited controls, BGMs baited with Mbita blend caught most mosquitoes (45 (29.5–70.25)), followed by BGMs baited with CO2 (42.5 (27.5–64)), Ifakara blend (31 (9.25–41.25)) and BG lure (16 (4–22)). BGM caught 51 (29.5–72.25) mosquitoes/night, when the attractants were dispensed using BG-Cartridges, compared to BG-Sachet (29.5 (24.75–40.5)), and nylon strips (27 (19.25–38.25)), in all cases being significantly superior to unbaited controls (p < 000.1). The findings demonstrate potential of the BGM as a sampling tool for African malaria vectors over the standard BGS trap. Its efficacy can be optimized by selecting appropriate odour baits and odour-dispensing systems

Titanium isotope constraints on the mafic sources and geodynamic origins of Archean crust

The timing and formation of Earth’s first continents during the Archean are subjects of significant debate. By examining titanium isotope variations in Archean Tonalite-Trondhjemite-Granodiorite (TTG) rocks and using advanced thermodynamic modelling, we can narrow down the processes involved and emphasise the role of mafic precursor compositions. In our study of Eoarchean Isua metabasalts and Itsaq tonalites in southern West Greenland, we observed a pattern of increasing Ti isotope enrichment with higher SiO2 content, resembling the compositions found in modern subduction zone rocks. Our modelling suggests that the Ti isotope variations in TTGs can be best explained by a combination of partial melting of low TiO2 metabasalts and subsequent crystallisation of tonalitic magmas, resulting in heavier Ti isotopes. This means that Ti isotopes help us distinguish the contributions of various mafic sources and fractional crystallisation during TTG formation. In the case of Itsaq tonalites and many other Eoarchean TTGs, low TiO2 tholeiitic metabasalts with arc-like characteristics likely represent the mafic source rocks, suggesting the formation of some of Earth’s earliest continental crust within a proto-subduction zone setting

Observing the distribution of mosquito bites on humans to inform personal protection measures against malaria and dengue vectors

Background Understanding mosquito biting behaviours is important for designing and evaluating protection methods against nuisance biting and mosquito-borne diseases (e.g. dengue, malaria and zika). We investigated the preferred biting sites by Aedes aegypti and Anopheles arabiensis on adult volunteers in standing or sleeping positions; and estimated the theoretical protection limits affordable from protective clothing or repellent-treated footwear. Methods Adult volunteers dressed in shorts and t-shirts were exposed to infection-free laboratory-reared mosquitoes inside screened chambers from 6am to noon (for day-biting Ae. aegypti) or 6pm to midnight (night-biting An. arabiensis). Attempted bites on different body parts were recorded. Comparative observations were made on same volunteers while wearing sandals treated with transfluthrin, a vapour-phase pyrethroid that kills and repels mosquitoes. Results An. arabiensis bites were mainly on the lower limbs of standing volunteers (95.9% of bites below the knees) but evenly-distributed over all exposed body surfaces when the volunteers were on sleeping positions (only 28.8% bites below knees). Ae. aegypti bites were slightly concentrated on lower limbs of standing volunteers (47.7% below knees), but evenly-distributed on sleeping volunteers (23.3% below knees). Wearing protective clothing that leave only hands and head uncovered (e.g. socks + trousers + long-sleeved shirts) could theoretically prevent 78–83% of bites during sleeping, and at least 90% of bites during non-sleeping hours. If the feet are also exposed, protection declines to as low as 36.3% against Anopheles. The experiments showed that transfluthrin-treated sandals reduced An. arabiensis by 54–86% and Ae. aegypti by 32–39%, but did not change overall distributions of bites. Conclusion Biting by An. arabiensis and Ae. aegypti occur mainly on the lower limbs, though this proclivity is less pronounced in the Aedes species. However, when hosts are on sleeping positions, biting by both species is more evenly-distributed over the exposed body surfaces. High personal protection might be achieved by simply wearing long-sleeved clothing, though protection against Anopheles particularly requires covering of feet and lower legs. The transfluthrin-treated footwear can reduce biting risk, especially by An. arabiensis. These findings could inform the design and use of personal protection tools (both insecticidal and non-insecticidal) against mosquitoes and mosquito-borne diseases

Videographic analysis of flight behaviours of host-seeking Anopheles arabiensis towards BG-Malaria trap.

The BG-Malaria trap (BGM) is an adaptation of the well-known BG-Sentinel trap (BGS) with greater trapping efficiencies for anopheline and culicine mosquitoes. Its continued optimization requires greater understanding of mosquito flight behaviors near it. We used three high-resolution infrared cameras (68 frames/second) to track flight behaviors of laboratory-reared Anopheles arabiensis females in vicinity of the BGM in comparison with BGS. Additional comparisons were done for BGM at 20, 40 and 80cm heights, and for BGMs baited with Ifakara blend plus CO2, CO2 alone, or no bait. More mosquitoes were observed near BGM than BGS. Both BGMs installed 20cm above the floor and baited with CO2 received more visits by host-seeking mosquitoes than the other BGMs evaluated in their respective experiments. Trap designs, height and attractants all influence mosquito activity in vicinity of the traps which can be readily visualized using infrared cameras to accelerate trap development and testing. The greater activity of host-seeking mosquitoes near BGM than BGS supports the proven superiority of BGM traps in field and semi-field settings

Evaluation of a simple polytetrafluoroethylene (PTFE)-based membrane for blood-feeding of malaria and dengue fever vectors in the laboratory

BACKGROUND: Controlled blood-feeding is essential for maintaining laboratory colonies of disease-transmitting mosquitoes and investigating pathogen transmission. We evaluated a low-cost artificial feeding (AF) method, as an alternative to direct human feeding (DHF), commonly used in mosquito laboratories. METHODS: We applied thinly-stretched pieces of polytetrafluoroethylene (PTFE) membranes cut from locally available seal tape (i.e. plumbers tape, commonly used for sealing pipe threads in gasworks or waterworks). Approximately 4 ml of bovine blood was placed on the bottom surfaces of inverted Styrofoam cups and then the PTFE membranes were thinly stretched over the surfaces. The cups were filled with boiled water to keep the blood warm (~37 degrees C), and held over netting cages containing 3-4 day-old inseminated adults of female Aedes aegypti, Anopheles gambiae (s.s.) or Anopheles arabiensis. Blood-feeding success, fecundity and survival of mosquitoes maintained by this system were compared against DHF. RESULTS: Aedes aegypti achieved 100% feeding success on both AF and DHF, and also similar fecundity rates (13.1 +/- 1.7 and 12.8 +/- 1.0 eggs/mosquito respectively; P > 0.05). An. arabiensis had slightly lower feeding success on AF (85.83 +/- 16.28%) than DHF (98.83 +/- 2.29%) though these were not statistically different (P > 0.05), and also comparable fecundity between AF (8.82 +/- 7.02) and DHF (8.02 +/- 5.81). Similarly, for An. gambiae (s.s.), we observed a marginal difference in feeding success between AF (86.00 +/- 10.86%) and DHF (98.92 +/- 2.65%), but similar fecundity by either method. Compared to DHF, mosquitoes fed using AF survived a similar number of days [Hazard Ratios (HR) for Ae. aegypti = 0.99 (0.75-1.34), P > 0.05; An. arabiensis = 0.96 (0.75-1.22), P > 0.05; and An. gambiae (s.s.) = 1.03 (0.79-1.35), P > 0.05]. CONCLUSIONS: Mosquitoes fed via this simple AF method had similar feeding success, fecundity and longevity. The method could potentially be used for laboratory colonization of mosquitoes, where DHF is unfeasible. If improved (e.g. minimizing temperature fluctuations), the approach could possibly also support studies where vectors are artificially infected with blood-borne pathogens

Correlations of mutations in katG, oxyR-ahpC and inhA genes and in vitro susceptibility in Mycobacterium tuberculosis clinical strains segregated by spoligotype families from tuberculosis prevalent countries in South America

Background Mutations associated with resistance to rifampin or streptomycin have been reported for W/Beijing and Latin American Mediterranean (LAM) strain families of Mycobacterium tuberculosis. A few studies with limited sample sizes have separately evaluated mutations in katG, ahpC and inhA genes that are associated with isoniazid (INH) resistance. Increasing prevalence of INH resistance, especially in high tuberculosis (TB) prevalent countries is worsening the burden of TB control programs, since similar transmission rates are noted for INH susceptible and resistant M. tuberculosis strains. Results We, therefore, conducted a comprehensive evaluation of INH resistant M. tuberculosis strains (n = 224) from three South American countries with high burden of drug resistant TB to characterize mutations in katG, ahpC and inhA gene loci and correlate with minimal inhibitory concentrations (MIC) levels and spoligotype strain family. Mutations in katG were observed in 181 (80.8%) of the isolates of which 178 (98.3%) was contributed by the katG S315T mutation. Additional mutations seen included oxyR-ahpC; inhA regulatory region and inhA structural gene. The S315T katG mutation was significantly more likely to be associated with MIC for INH ≥2 μg/mL. The S315T katG mutation was also more frequent in Haarlem family strains than LAM (n = 81) and T strain families. Conclusion Our data suggests that genetic screening for the S315T katG mutation may provide rapid information for anti-TB regimen selection, epidemiological monitoring of INH resistance and, possibly, to track transmission of INH resistant strains.Fil: Dalla Costa, Elis R. State Foundation for Production and Research in Health (FEPPS); Brasil.Fil: Ribeiro, Marta O. State Foundation for Production and Research in Health (FEPPS); Brasil.Fil: Silva, Márcia S. N. State Foundation for Production and Research in Health (FEPPS); Brasil.Fil: Arnold, Liane S. State Foundation for Production and Research in Health (FEPPS); Brasil.Fil: Rostirolla, Diana C. State Foundation for Production and Research in Health (FEPPS); Brasil.Fil: Cafrune, Patricia I. State Foundation for Production and Research in Health (FEPPS); Brasil.Fil: Espinoza, Roger C. Blufstein Clinic Laboratory; Perú.Fil: Palaci, Moises. Federal University of Espírito Santo; Brasil.Fil: Telles, Maria A. Adolfo Lutz Institute; Brasil.Fil: Ritacco, Viviana. ANLIS Dr.C.G.Malbrán. Instituto Nacional de Enfermedades Infecciosas. Servicio de Micobacterias; Argentina.Fil: Suffys, Philip N. Oswaldo Cruz Institute; Brasil.Fil: Lopes, Maria L. Evandro Chagas Institute; Brasil.Fil: Campelo, Creuza L. LACEN Ceará; BrasilFil: Miranda, Silvana S. Federal University of Minas Gerais; Brasil.Fil: Kremer, Kristin. National Institute for Public Healthand the Environment (RIVM). Mycobacteria Reference Unit (CIb-LIS); Países Bajos.Fil: Almeida da Silva, Pedro E. Federal Foundation of Rio Grande; Brasil.Fil: de Souza Fonseca, Leila. Federal University of Rio de Janeiro. Tuberculosis Academic Program; Brasil.Fil: Ho, John L. Cornell University; Estados Unidos.Fil: Kritski, Afrânio L. Federal University of Rio de Janeiro. Tuberculosis Academic Program; Brasil.Fil: Rossetti, María L. R. State Foundation for Production and Research in Health (FEPPS); Brasil

Evaluation of a push–pull system consisting of transfluthrin-treated eave ribbons and odour-baited traps for control of indoor- and outdoor-biting malaria vectors

Background: Push–pull strategies have been proposed as options to complement primary malaria prevention tools, indoor residual spraying (IRS) and long-lasting insecticide-treated nets (LLINs), by targeting particularly early-night biting and outdoor-biting mosquitoes. This study evaluated different configurations of a push–pull system consisting of spatial repellents [transfluthrin-treated eave ribbons (0.25 g/m2 ai)] and odour-baited traps (CO2-baited BG-Malaria traps), against indoor-biting and outdoor-biting malaria vectors inside large semi-field systems. Methods: Two experimental huts were used to evaluate protective efficacy of the spatial repellents (push-only), traps (pull-only) or their combinations (push–pull), relative to controls. Adult volunteers sat outdoors (1830 h–2200 h) catching mosquitoes attempting to bite them (outdoor-biting risk), and then went indoors (2200 h–0630 h) to sleep under bed nets beside which CDC-light traps caught host-seeking mosquitoes (indoor-biting risk). Number of traps and their distance from huts were varied to optimize protection, and 500 laboratory-reared Anopheles arabiensis released nightly inside the semi-field chambers over 122 experimentation nights. Results: Push-pull offered higher protection than traps alone against indoor-biting (83.4% vs. 35.0%) and outdoor-biting (79% vs. 31%), but its advantage over repellents alone was non-existent against indoor-biting (83.4% vs. 81%) and modest for outdoor-biting (79% vs. 63%). Using two traps (1 per hut) offered higher protection than either one trap (0.5 per hut) or four traps (2 per hut). Compared to original distance (5 m from huts), efficacy of push–pull against indoor-biting peaked when traps were 15 m away, while efficacy against outdoor-biting peaked when traps were 30 m away. Conclusion: The best configuration of push–pull comprised transfluthrin-treated eave ribbons plus two traps, each at least 15 m from huts. Efficacy of push–pull was mainly due to the spatial repellent component. Adding odour-baited traps slightly improved personal protection indoors, but excessive trap densities increased exposure near users outdoors. Given the marginal efficacy gains over spatial repellents alone and complexity of push–pull, it may be prudent to promote just spatial repellents alongside existing interventions, e.g. LLINs or non-pyrethroid IRS. However, since both transfluthrin and traps also kill mosquitoes, and because transfluthrin can inhibit blood-feeding, field studies should be done to assess potential community-level benefits that push–pull or its components may offer to users and non-users

Small-scale field evaluation of transfluthrin-treated eave ribbons and sandals for the control of malaria vectors in rural Tanzania

Background: Early-evening and outdoor-biting mosquitoes may compromise the effectiveness of frontline malaria interventions, notably insecticide-treated nets (ITNs). This study aimed to evaluate the efficacy of low-cost insecticide-treated eave ribbons and sandals as supplementary interventions against indoor-biting and outdoor-biting mosquitoes in south-eastern Tanzania, where ITNs are already widely used. Methods: This study was conducted in three villages, with 72 households participating (24 households per village). The households were divided into four study arms and assigned: transfluthrin-treated sandals (TS), transfluthrin-treated eave ribbons (TER), a combination of TER and TS, or experimental controls. Each arm had 18 households, and all households received new ITNs. Mosquitoes were collected using double net traps (to assess outdoor biting), CDC light traps (to assess indoor biting), and Prokopack aspirators (to assess indoor resting). Protection provided by the interventions was evaluated by comparing mosquito densities between the treatment and control arms. Additional tests were done in experimental huts to assess the mortality of wild mosquitoes exposed to the treatments or controls. Results: TERs reduced indoor-biting, indoor-resting and outdoor-biting Anopheles arabiensis by 60%, 73% and 41%, respectively, while TS reduced the densities by 18%, 40% and 42%, respectively. When used together, TER & TS reduced indoor-biting, indoor-resting and outdoor-biting An. arabiensis by 53%, 67% and 57%, respectively. Protection against Anopheles funestus ranged from 42 to 69% with TER and from 57 to 74% with TER & TS combined. Mortality of field-collected mosquitoes exposed to TER, TS or both interventions was 56–78% for An. arabiensis and 47–74% for An. funestus. Conclusion: Transfluthrin-treated eave ribbons and sandals or their combination can offer significant household-level protection against malaria vectors. Their efficacy is magnified by the transfluthrin-induced mortality, which was observed despite the prevailing pyrethroid resistance in the study area. These results suggest that TER and TS could be useful supplementary tools against residual malaria transmission in areas where ITN coverage is high but additional protection is needed against early-evening and outdoor-biting mosquitoes. Further research is needed to validate the performance of these tools in different settings, and assess their long-term effectiveness and feasibility for malaria control

Differential Conservation and Divergence of Fertility Genes boule and dazl in the Rainbow Trout

10.1371/journal.pone.0015910PLoS ONE61