PMI Activity TZ-1,2: IRS and LLIN: Integration of Methods and Insecticide Mode of Actions for Control of African Malaria Vector Mosquitoes

Long lasting Insecticidal nets (LLINs) and indoor residual spraying (IRS) are the preferred techniques for malaria vector control in Africa, where their application has a proven contribution to the recent significant reductions in the burden of the disease. Even though both methods are commonly used together in the same households, evidence of improved malaria control due to the use of combinations as opposed to use of either method alone has been minimal and inconclusive.To measure the mode of action of three classes of insecticides used for IRS at the WHO recommended dose: the organochlorine DDT 70 wettable powder (AVIMA, South Africa) at 2g/m2; the pyrethroid lambda-cyhalothrin capsule suspension ICON CS, (Syngenta, Switzerland), at 0.03g/m2; and the organophosphate pirimiphos-methyl (PM) emulsified concentrate, also known as actellic (Syngenta, Switzerland), at 2g/m2 used alone or in combination with three leading LLIN brands: PermaNet 2.0® nets (Vastergaard, Switzerland), Olyset® nets (manufactured by A-Z, Tanzania), and Icon Life® nets (Bestnet Europe ltd, Denmark). All LLINS were used intact and were not subjected to repeated washing to reflect their optimum performance. The control was untreated polyester net. Data were collected from experimental huts developed during the project to measure both behavioral and toxic modes of actions of insecticides in Southern Tanzania. The primary malaria vector is Anopheles arabiensis with >90% susceptibility to insecticides of all classes at diagnostic doses in WHO susceptibility assays. Two rounds of data collection were performed: 1) 4 months during the dry season 2) six months during the wet season. Data generated from the experimental hut studies were analysed with Poisson-lognormal generalized linear mixed effects models (GLMM). Data was also simulated using deterministic mathematical model to measure potential impacts of each IRS, LLIN and combination thereof on malaria at a community level. Bite prevention (feeding inhibition): During both rounds, all the IRS treatments, LLINs and the controls (which consisted of intact untreated mosquito nets), provided greater than 99% protection from potentially infectious bites by the malaria vector, An. arabiensis, for the entire duration of the study. Most of the mosquitoes were caught inside the exit traps as opposed to inside the experimental huts, regardless of whether the huts were had LLINs, IRS or non-insecticidal nets. More than 95% of An. arabiensis, Culex pipiens quinquefasciatus and Mansonia africana / uniformis mosquitoes were caught inside the exit traps while exiting the huts. Toxicity: All IRS treatments, all the LLINs and the majority of LLIN/IRS combinations significantly increased proportions of dead An. arabiensis mosquitoes, relative to the control huts. The most toxic IRS relative to the controls was PM (RR = 2.21 (1.82 – 2.68), P < 0.001), followed by ICON CS (RR = 1.55 (1.27 – 1.89), P < 0.001) and then DDT (RR = 1.44 (1.18 – 1.77), P < 0.001). The most toxic LLIN relative to the controls was PermaNet 2.0® nets (RR = 1.65 (1.58 – 1.74), P < 0.001), followed by Icon Life® nets (RR = 1.55 (1.42 – 1.69), P < 0.001) and then Olyset® nets (RR = 1.33 (1.12 – 1.47), P < 0.001). Combinations of IRS and LLINs relative to LLINs alone: In most cases, there was no significant increase in An. arabiensis mortality in huts combining LLINs plus IRS, relative to huts having LLINs only, except in cases where the specific IRS treatment was PM. Addition of PM significantly increased proportional mortality of An. arabiensis when combined with Olyset® nets (RR = 1.38 (1.14 – 1.65), P = 0.001), PermaNet 2.0® nets (RR = 1.42 (1.18 – 1.71), P <0.001) and Icon Life® (RR = 1.24 (1.03 – 1.49), P = 0.023). Combinations of LLINs and DDT or lambda cyhalothrin resulted in marginal increases in An. arabiensis mortality relative to huts with LLINs alone although none of these combinations resulted in a statistically significant increase. Combinations of IRS and LLINs relative to IRS alone: There was a trend of significant increases in An. arabiensis mortality in huts having IRS plus LLINs, relative to huts having just the IRS alone, except for the combinations of 1) Olyset® with ICON CS, 2) DDT with Olyset® or 3) DDT with Icon Life® nets. In the huts that had been sprayed with PM, there was a significant increase in An. arabiensis mortality whenever Icon Life® nets (RR = 1.39 (1.18 – 1.63), P < 0.001), Olyset® nets (RR = 1.32 (1.13 – 1.55), P = 0.001) or PermaNet 2.0® nets (RR = 1.26 (1.08 – 1.48), P = 0.004) were added, relative to the huts where PM IRS was used alone. Similarly, in the huts that had been sprayed with ICON CS, there was a significant increase in An. arabiensis mortality in combination with Icon Life® nets (RR = 1.43 (1.19 – 1.73), P < 0.001) or PermaNet 2.0® nets (RR = 1.70 (1.35 – 2.13), P < 0.001), but not Olyset® nets (RR = 1.16 (0.92 – 1.45), P = 0.210), relative to the IRS alone. In huts sprayed with DDT, none of the LLINs significantly improved proportional mortality of the An. Arabiensis mosquitoes, except PermaNet 2.0® nets (RR = 1.18 (1.06 – 1.32), P = 0.003). Residual efficacy bioassays of IRS: All IRS formulations were highly effective during the first month after spraying and rapidly decayed losing most activity within 1-3 months. In month 1, all An. arabiensis exposed to palm ceilings sprayed with either PM or ICON CS died, and 85% were killed by DDT (despite full susceptibility most likely because it flaked away). On mud walls sprayed with the same chemicals, 100%, 90.0% and 97.5% mortality was observed, respectively, during the first month. Activity of the IRS declined significantly so that by the third month, PM on palm and mud killed 42.5% and 55.0% of exposed An. arabiensis, respectively. ICON CS killed only 46.3% on palm and 52.5% on mud walls. By month 6, PM had nearly entirely decayed, killing only 7.5% of An. arabiensis exposed to sprayed palm ceilings and 27.5% of those exposed to sprayed mud walls; ICON CS killed 30.0% on ceilings and 27.5% on walls. DDT had a longer residual action, killing 42.5% of An. arabiensis exposed to sprayed ceilings, and 36.3% of those exposed to sprayed walls after 6 months. Residual efficacy bioassays of LLINs: While all the LLINs generally performed better (i.e. killed more mosquitoes) on wire frame assays than on the cone assays, their activity rapidly deteriorated by the second month of use relative to new nets. Only PermaNet® nets retained mosquitocidal efficacy of >80% by the sixth month of net use (killing 92.7% on wire ball tests and 84% on cone assays). All the LLINs however retained very high knock-down rates (> 90% in wire ball tests and >80% in cone tests) on the exposed mosquitoes, except Olyset® nets whose knock-down activity reduced to 72.7% on wire ball tests and 62% on cone tests by the sixth month. Both the field studies and the model simulations showed that any synergies or redundancies resulting from LLIN/IRS combinations are primarily a function of modes of action of active ingredients used in the two interventions. None of the IRS or LLINs tested was deterrent so they do not protect by keeping mosquitoes from houses in this setting. Very few mosquitoes were able to obtain a blood meal due to the use of intact LLINs and untreated control nets. Therefore, where households are correctly using and maintaining LLINs there is no added value in the additional application of IRS unless the IRS chemical is highly toxic and non-irritant, as is PM. This compound consistently increased mosquito mortality in combination with any LLIN even though mosquitoes did not rest indoors as they were unable to obtain a blood meal. The average duration of effect of insecticides in this setting was 3 months, far lower than that stated by the manufacturers, so IRS should be carefully timed. Where IRS is the pre-existing intervention, providing households with additional LLINs confers additional protection. Therefore, IRS households should always be supplemented with nets, preferably LLINs, which not only protect house occupants against mosquito bites, but also kill additional mosquitoes. Finally, where resources are limited, priority should be given to providing everybody with LLINs and ensuring that these nets are consistently and appropriately used, rather than trying to implement both LLINs and IRS in the same community at the same time.\ud \u

Biologically meaningful coverage indicators for eliminating malaria transmission.

Mosquitoes, which evade contact with long-lasting insecticidal nets and indoor residual sprays, by feeding outdoors or upon animals, are primary malaria vectors in many tropical countries. They can also dominate residual transmission where high coverage of these front-line vector control measures is achieved. Complementary strategies, which extend insecticide coverage beyond houses and humans, are required to eliminate malaria transmission in most settings. The overwhelming diversity of the world's malaria transmission systems and optimal strategies for controlling them can be simply conceptualized and mapped across two-dimensional scenario space defined by the proportion of blood meals that vectors obtain from humans and the proportion of human exposure to them which occurs indoors

Implications of bio-efficacy and persistence of insecticides when indoor residual spraying and longlasting insecticide nets are combined for malaria prevention.

Bio-efficacy and residual activity of insecticides used for indoor residual spraying (IRS) and long-lasting insecticide nets (LLINs) were assessed against laboratory-reared and wild populations of the malaria vector, Anopheles arabiensis in south eastern Tanzania. Implications of the findings are examined in the context of potential synergies and redundancies where IRS and LLINs are combined. METHODS: Bioassays were conducted monthly for six months on three LLIN types (Olyset(R) PermaNet 2.0(R),and Icon Life(R)) and three IRS treatments (2 g/m2 pirimiphos-methyl, 2 g/m2 DDT and 0.03 g/m2 lambda-cyhalothrin, sprayed on mud walls and palm ceilings of experimental huts). Tests used susceptible laboratory-reared An. arabiensis exposed in cones (nets and IRS) or wire balls (nets only). Susceptibility of wild populations was assessed using WHO diagnostic concentrations and PCR for knock-down resistance (kdr) genes. IRS treatments killed [greater than or equal to] 85% of mosquitoes exposed on palm ceilings and [greater than or equal to] 90% of those exposed on mud walls, but up to 50% of this toxicity decayed within 1-3 months, except for DDT. By 6th month, only 7.5%, 42.5% and 30.0% of mosquitoes died when exposed to ceilings sprayed with pirimiphos-methyl, DDT or lambda-cyhalothrin respectively, while 12.5%, 36.0% and 27.5% died after exposure to mud walls sprayed with the same insecticides. In wire-ball assays, mortality decreased from 98.1% in 1st month to 92.6% in 6th month in tests on PermaNet 2.0(R), from 100% to 61.1% on Icon Life(R) and from 93.2% to 33.3% on Olyset(R) nets. In cone bioassays, mortality reduced from 92.8% in 1st month to 83.3% in 6th month on PermaNet 2.0(R), from 96.9% to 43.80% on Icon Life(R) and from 85.6% to 14.6% on Olyset(R). Wild An. arabiensis were 100% susceptible to DDT, 95.8% to deltamethrin, 90.2% to lambda cyhalothrin and 95.2% susceptible to permethrin. No kdr gene mutations were detected. CONCLUSIONS: In bioassays where sufficient contact with treated surfaces is assured, LLINs and IRS kill high proportions of susceptible An. arabiensis mosquitoes, though these efficacies decay gradually for LLINs and rapidly for IRS. It is, therefore, important to always add intact nets in sprayed houses, guaranteeing protection even after the IRS decays, and to ensure accurate timing, quality control and regular re-spraying in IRS programmes. By contrast, adding IRS in houses with intact LLINs is unlikely to improve protection relative to LLINs alone, since there is no guarantee that unfed vectors would rest long enough on the sprayed surfaces, and because of the rapid IRS decay. However, there is need to clarify these effects using data from observations of free flying mosquitoes in huts. Physiological susceptibility of An. arabiensis in the area remains 100% against DDT, but is slightly reduced against pyrethroids, necessitating caution over possible spread of resistance. The loss of LLIN toxicity, particularly Olyset(R) nets suggests that protection offered by these nets against An. arabiensis may be primarily due to physical bite prevention rather than insecticidal efficacy

Plant-based insect repellents: a review of their efficacy, development and testing

Plant-based repellents have been used for generations in traditional practice as a personal protection measure against host-seeking mosquitoes. Knowledge on traditional repellent plants obtained through ethnobotanical studies is a valuable resource for the development of new natural products. Recently, commercial repellent products containing plant-based ingredients have gained increasing popularity among consumers, as these are commonly perceived as “safe” in comparison to long-established synthetic repellents although this is sometimes a misconception. To date insufficient studies have followed standard WHO Pesticide Evaluation Scheme guidelines for repellent testing. There is a need for further standardized studies in order to better evaluate repellent compounds and develop new products that offer high repellency as well as good consumer safety. This paper presents a summary of recent information on testing, efficacy and safety of plant-based repellents as well as promising new developments in the field

Archaeogenetic evidence of ancient Nubian barley evolution from six to two-row indicates local adaptation

Background Archaeobotanical samples of barley (Hordeum vulgare L.) found at Qasr Ibrim display a two-row phenotype that is unique to the region of archaeological sites upriver of the first cataract of the Nile, characterised by the development of distinctive lateral bracts. The phenotype occurs throughout all strata at Qasr Ibrim, which range in age from 3000 to a few hundred years. Methodology and Findings We extracted ancient DNA from barley samples from the entire range of occupancy of the site, and studied the Vrs1 gene responsible for row number in extant barley. Surprisingly, we found a discord between the genotype and phenotype in all samples; all the barley had a genotype consistent with the six-row condition. These results indicate a six-row ancestry for the Qasr Ibrim barley, followed by a reassertion of the two-row condition. Modelling demonstrates that this sequence of evolutionary events requires a strong selection pressure. Conclusions The two-row phenotype at Qasr Ibrim is caused by a different mechanism to that in extant barley. The strength of selection required for this mechanism to prevail indicates that the barley became locally adapted in the region in response to a local selection pressure. The consistency of the genotype/phenotype discord over time supports a scenario of adoption of this barley type by successive cultures, rather than the importation of new barley varieties associated with individual cultures

Fusion of the NUP98 gene with the LEDGF/p52 gene defines a recurrent acute myeloid leukemia translocation

BACKGROUND: The NUP98 gene is involved in multiple rearrangements in haematological malignancy. The leukemic cells in an acute myeloid leukemia (AML) patient with a t(9;11)(p22;p15) were recently shown to have a fusion between the NUP98 gene and the LEDGF gene but it was not demonstrated that this fusion was recurrent in other leukaemia patients with the same translocation. RESULTS: We used RT-PCR to analyse the leukemic cells from an AML patient who presented with a cytogenetically identical translocation as the sole chromosomal abnormality. A NUP98-LEDGF fusion transcript was observed and confirmed by sequencing. The reciprocal transcript was also observed. The fusion transcript was not detectable during remission and recurred at relapse. The breakpoints in the NUP98 and LEDGF genes were different to those previously reported. The NUP98 breakpoint occurs in the intron between exons 8 and 9. It is the most 5' breakpoint reported in a translocation involving the NUP98 gene. All of the LEDGF gene is included in the fusion except for exon 1 which codes for the first 24 amino terminal amino acids. CONCLUSIONS: Our results show that fusion of the NUP98 and LEDGF genes is a new recurrent translocation in AML

An experimental hut study to quantify the effect of DDT and airborne pyrethroids on entomological parameters of malaria transmission

&lt;b&gt;Background&lt;/b&gt;&lt;p&gt;&lt;/p&gt; Current malaria vector control programmes rely on insecticides with rapid contact toxicity. However, spatial repellents can also be applied to reduce man-vector contact, which might ultimately impact malaria transmission. The aim of this study was to quantify effects of airborne pyrethroids from coils and DDT used an indoor residual spray (IRS) on entomological parameters that influence malaria transmission.&lt;p&gt;&lt;/p&gt; &lt;b&gt;Methods&lt;/b&gt;&lt;p&gt;&lt;/p&gt; The effect of Transfluthrin and Metofluthrin coils compared to DDT on house entry, exit and indoor feeding behaviour of Anopheles gambiae sensu lato were measured in experimental huts in the field and in the semi-field. Outcomes were deterrence - reduction in house entry of mosquitoes; irritancy or excito-repellency – induced premature exit of mosquitoes; blood feeding inhibition and effect on mosquito fecundity.&lt;p&gt;&lt;/p&gt; &lt;b&gt;Results&lt;/b&gt;&lt;p&gt;&lt;/p&gt; Transfluthrin coils, Metofluthrin coils and DDT reduced human vector contact through deterrence by 38%, 30% and 8%, respectively and induced half of the mosquitoes to leave huts before feeding (56%, 55% and 48%, respectively). Almost all mosquitoes inside huts with Metofluthrin and Transfluthrin coils and more than three quarters of mosquitoes in the DDT hut did not feed, almost none laid eggs and 67%, 72% and 70% of all mosquitoes collected from Transfluthrin, Metofluthrin and DDT huts, respectively had died after 24 hours.&lt;p&gt;&lt;/p&gt; &lt;b&gt;Conclusion&lt;/b&gt;&lt;p&gt;&lt;/p&gt; This study highlights that airborne pyrethroids and DDT affect a range of anopheline mosquito behaviours that are important parameters in malaria transmission, namely deterrence, irritancy/excito-repellency and blood-feeding inhibition. These effects are in addition to significant toxicity and reduced mosquito fecundity that affect mosquito densities and, therefore, provide community protection against diseases for both users and non-users. Airborne insecticides and freshly applied DDT had similar effects on deterrence, irritancy and feeding inhibition. Therefore, it is suggested that airborne pyrethroids, if delivered in suitable formats, may complement existing mainstream vector control tools