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

The quality of drinking water used by the communities in some regions of Uganda

The study was done to assess the suitability of drinking water sources used by some communities in Uganda and the associated consumption risks. Water samples were collected, treated and tested according to standard methods of the American Public Health Association (APHA). Results of physicochemical and microbiological parameters were: NOu- 3 (0.01-4.6 mg/l); turbidity (&lt; 5-97.6NTU); Total dissolved solids (59- 420.9 mg/l); conductivity (28-760 µS/cm); pH (5.3-7.2); temperature (23-25.90 °C), total coliform (0-940 cfu/100ml), faecal coliform (0-200 cfu/100ml). Risk of Contamination (ROC) assessment agreed with water quality analysis that found boreholes to be the safest (&lt;1 CFU/100mL) water source, followed in order by rainwater, standpipe taps and protected springs. Shallow wells, unprotected springs and surface water (e.g. streams) were high risk (≥100 CFU/100 mL) water sources. Nitrate.nitrogen, faecal coliform and total coliform were higher than WHO standards for drinking water in most of the water springs and wells. The management of community water sources is discussed.Keywords: Bacteriological, risk of contamination, physicochemical, communities water sources

Impact of Industrial Effluents on Water Quality of Streams in Nakawa-Ntinda, Uganda

In Uganda industries generate large proportions of solid wastes and wastewater. The wastes are disposed into the environment untreated leading to pollution. This study was undertaken to examine selectedphysicochemical parameters of streams that receive effluents from different categories of industries in Nakawa -Ntinda industrial area of Kampala. the stream water quality were pH (3.68 -12.41mg/l), EC (212 - 4633 ìScm-1), turbidity (20.9 - 715.9NTU), colour (72 - 958TCU), BOD (16.4 -325.5 mg/l), COD (39 -1351mg/l), TN (0.45 - 32.63mg/l), TP (0.078 - 1.674mg/l), Na (0.59 - 53.04mg/l), Cl (11.68 - 31.08mg/l), Ca (6.38- 38.75mg/l), Pb (0.039 - 0.256mg/l), Cu (0.015 - 0.52 mg/l) and Cd (below detection limit). Food and beverage industries discharged effluents in noncompliance to Ugandan national regulations (BOD, COD, EC, Nitrogen, Turbidity and Colour), while chemical and pharmaceutical industries did not comply as regards heavy metals. All the industries did not have any wastewater treatment plant. This study reveals a scenario typical of most industries in developing nations where enforcement of environmental regulations are deficient. To avoid pollution Regulatory Authorities should closely monitor compliance by industries

Monitoring Residual Chlorine Decay and Coliform Contamination in Water Distribution Network of Kampala, Uganda

The study was undertaken to examine water quality in the distribution network of Kampala City by assessing five storage reservoirs and four consumer taps. The aim was to evaluate residual chlorine decay andrelate it to the risk of recontamination. Physicochemical quality of water in the distribution network was temperature 25.6(24.23-28.66) pH 6.6 (6.5-7.1); turbidity 1.9 (0.5-4.5) NTU; colour 17.2 (2.0-54) PtCo, ammonia0.02 (0.0-0.05) mgl-1, and Fe2+ 0.005 (0-0.0.08) mgl-1. Residual chlorine decay was significant between the Water Treatment Plant (WTP) and the storage tanks (Total Chlorine, F=35.67, P< 0.05; Free Chlorine, F=37.97,

Microbial safety assessment of recreation water at Lake Nabugabo, Uganda

This study assessed the microbial safety of Lake Nabugabo beaches for recreation. Faecal microbial indicators and physico-chemical characteristics of beach recreational water were determined. Water sampling was done between 10.00 and 11.30 h and 1700 and 18.00 h. Data was analysed using student t-tests, ANOVA and spearman correlation (at 95%). Results were: total coliform (10.5-15.8 CFU/100 ml), faecal coliform (10-12.5 CFU/100 ml), Escherichia coli (0 2.63 CFU/100 ml), faecal streptococci (0-1.5 CFU/100 ml), all significantly different (P&lt;0.05) from the control and electrical conductivity (27-32.6 μS/cm), pH (7.1), turbidity (12.6-26 NTU), total dissolved solids (13.2-15.4 mg/l), total suspended solids (12.6 - 13.4), colour (10.3 Pt-Co), alkalinity (29.3 mg/l), hardness (CaCO3) (32.5 mg/l), total nitrogen (1.3 mg/l), ammonium-N (0.6 mg/l), nitrate (0.05 mg/l), total phosphorus (0.8 mg/l), orthophosphates (0.02 mg/l), iron (0.2-0.3 mg/l), calcium (1.2-1.8 mg/l), magnesium (0.4-0.6 mg/l), sodium (1.2-2 mg/l), potassium (1.8-2.6 mg/l), all not significantly different (P &gt; 0.05) from the control. Total coliforms and faecal streptococci exhibited significant correlation with TSS (r = 0.9, p = 0.04). Results indicate that Lake Nabugabo water is safe (WHO, US-EPA) for recreation.Keywords: Lake Nabugabo, microbial safety assessment, recreation water, water quality

DIFFERENTIAL CROSS SECTIONS FOR ELASTIC ELECTRON SCATTERING BY A CALCIUM ATOM AT LOW ENERGY RANGE.

In this study the distorted wave method was applied in calculation of the differential cross sections (DCS) for elastic scattering of electron by a calcium atom at electron impact energies of 10, 15, 20, and 40 eV. At lower incident energies, 10, 15, and 20 eV the present DCS results are not in good agreement with other theoretical and experimental results. However, at 40 eV the present DCS results are in good agreement with other theoretical and experimental results. Key words: Cross-sections, distortion potential, distorted wave, static potential and spherical harmonics. DOI: 10.7176/APTA/83-09 Publication date: September 29th 202

Comparative Field Evaluation of Combinations of Long-Lasting Insecticide Treated Nets and Indoor Residual Spraying, Relative to Either Method Alone, for Malaria Prevention in an Area where the main Vector is Anopheles Arabiensis.

Long-lasting insecticidal nets (LLINs) and indoor residual spraying (IRS) are commonly used together in the same households to improve malaria control despite inconsistent evidence on whether such combinations actually offer better protection than nets alone or IRS alone. Comparative tests were conducted using experimental huts fitted with LLINs, untreated nets, IRS plus untreated nets, or combinations of LLINs and IRS, in an area where Anopheles arabiensis is the predominant malaria vector species. Three LLIN types, Olyset®, PermaNet 2.0® and Icon Life® nets and three IRS treatments, pirimiphos-methyl, DDT, and lambda cyhalothrin, were used singly or in combinations. We compared, number of mosquitoes entering huts, proportion and number killed, proportions prevented from blood-feeding, time when mosquitoes exited the huts, and proportions caught exiting. The tests were done for four months in dry season and another six months in wet season, each time using new intact nets. All the net types, used with or without IRS, prevented >99% of indoor mosquito bites. Adding PermaNet 2.0® and Icon Life®, but not Olyset® nets into huts with any IRS increased mortality of malaria vectors relative to IRS alone. However, of all IRS treatments, only pirimiphos-methyl significantly increased vector mortality relative to LLINs alone, though this increase was modest. Overall, median mortality of An. arabiensis caught in huts with any of the treatments did not exceed 29%. No treatment reduced entry of the vectors into huts, except for marginal reductions due to PermaNet 2.0® nets and DDT. More than 95% of all mosquitoes were caught in exit traps rather than inside huts. Where the main malaria vector is An. arabiensis, adding IRS into houses with intact pyrethroid LLINs does not enhance house-hold level protection except where the IRS employs non-pyrethroid insecticides such as pirimiphos-methyl, which can confer modest enhancements. In contrast, adding intact bednets onto IRS enhances protection by preventing mosquito blood-feeding (even if the nets are non-insecticidal) and by slightly increasing mosquito mortality (in case of LLINs). The primary mode of action of intact LLINs against An. arabiensis is clearly bite prevention rather than insecticidal activity. Therefore, where resources are limited, priority should be to ensure that everyone at risk consistently uses LLINs and that the nets are regularly replaced before being excessively torn. Measures that maximize bite prevention (e.g. proper net sizes to effectively cover sleeping spaces, stronger net fibres that resist tears and burns and net use practices that preserve net longevity), should be emphasized

Insecticide-Treated Nets Can Reduce Malaria Transmission by Mosquitoes Which Feed Outdoors

Insecticide treated nets (ITNs) represent a powerful means for controlling malaria in Africa because the mosquito vectors feed primarily indoors at night. The proportion of human exposure that occurs indoors, when people are asleep and can conveniently use ITNs, is therefore very high. Recent evidence suggests behavioral changes by malaria mosquito populations to avoid contact with ITNs by feeding outdoors in the early evening. We adapt an established mathematical model of mosquito behavior and malaria transmission to illustrate how ITNs can achieve communal suppression of malaria transmission exposure, even where mosquito evade them and personal protection is modest. We also review recent reports from Tanzania to show that conventional mosquito behavior measures can underestimate the potential of ITNs because they ignore the importance of human movements

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