Field tests were conducted to compare the degree of protection from bites of Mansonia species and Anopheles maculatus by applying two repellent/insecticidal bars, MOSBAR and MOSKIL, to exposed arms and legs. Human test subjects were exposed to natural populations of mosquitos for an 8-hour night time period while using the repellent/insecticidal bars. MOSBAR gave good protection against the bites of Mansonia and An. maculatus. MOSKIL was effective against An. maculatus but not against Mansonia. High mortality was observed among the mosquitos collected from human test subjects treated with the repellent/insecticidal bars. Use of MOSBAR in terms of cost-effectiveness and safety by field and health workers entering into malaria and filariasis endemic areas is discussed.
Vector control is still the principal method to control dengue and chemical insecticides, especially the
pyrethroids such as permethrin are the forerunners of mosquito control agent. Intensive and extensive use
of pyrethroids often result in resistance, thereby hampering control efforts. The present study was
conducted to evaluate the susceptible status of Aedes aegypti, the primary vector of dengue against
permethrin. A nationwide mosquito sampling via ovitrapping was conducted in 12 dengue hotspots across 5
states in Peninsular Malaysia. Field collected Aedes eggs were hatched and reared until L3 larval and further
identified it species. Adult F0 Aedes aegypti were reared until F1 progeny and the female were used in
adult assay, performed according to World Health Organization (WHO) protocol as to determine the
resistance level. The laboratory strain maintained for more than 1000 generations that were susceptible to
permethrin served as the control strain. Evaluation of resistance ratio was assessed by comparing the
knockdown rate with laboratory susceptible strain. In this present study, 70% ofAe. aegypti population from
dengue hotspots was highly resistance to permethrin. The study clearly demonstrated that widespread of
permethrin resistant Ae. aegypti in Malaysian mosquito’s population, indicating the need of implementing
an efficient pyrethroid resistance management.
Chemical insecticides are still considered as important control agents for malaria vector control. However, prolonged use of these chemicals may select mosquito vectors for resistance. In this study, susceptibility status of adult Anopheles maculatus collected from 9 localities in peninsular Malaysia, viz., Jeli, Temerloh, Pos Banun, Senderut, Jeram Kedah, Segamat, Kota Tinggi, Kluang and Pos Lenjang were determined using the standard WHO bioassay method in which the adult mosquitoes were exposed to standard insecticide impregnated papers malathion, permethrin, DDT and deltamethrin--at pre-determined diagnostic dosage. Deltamethrin was most effective insecticide among the four insecticides tested, with the LT50 of 29.53 min, compared to malathion (31.67 min), DDT (47.76 min) and permethrin (48.01 min). The effect of all insecticides on the laboratory strain was greater (with all insecticides demonstrated LT50 < 1 hour) than the field strains (deltamethrin 32.7, malathion 53.0, permethrin 62.0, DDT 67.4 min). An. maculatus exhibited low degree of resistance to all test insecticides, indicating that these chemical insecticides are still effective in the control of malaria vector.
Dengue and dengue haemorrhagic fever are common and serious arboviral diseases endemic in a number of countries situated in both the tropical and subtropical belts.
Wild caught female Culex quinquefasciatus (Say) from Kuala Lumpur were blood fed and reared in the insectarium. The late third stage of the F1 larvae which survived the high selection pressure of malathion and permethrin were reared and colonies were established from adults that emerged. Larvae from these colonies were then subjected in the subsequent 9 generations to higher selection pressure. The rate of resistance development were measured by LC50 value of larval bioassay, LT50 value of adult bioassay and the frequency of the elevated esterase levels. In another set of experiments using the same batch of Culex mosquitos, the larvae were not exposed to any insecticides and the decrease in resistance rate was monitored in each subsequent 9 generations by using similar methods. The heterozygous standard laboratory strain was selected for susceptibility using the single raft sib-selection method. The result showed that the field collected F1 generation was 96.0 and 6.3 fold more resistant to malathion and permethrin, respectively. After selection for about 9 generations the resistance ratio to malathion and permethrin was 6.2 and 767.3 fold more compared to the LC50 values of F1 generations, respectively. Esterase in F1 larvae was 6.0 fold more than the standard laboratory strain.
Glutathione S-transferases (GSTs) are a family of enzymes that function in the detoxification of variety of electrophilic substrates. In the present work, we report a novel zeta-like GST (designated as KKSG9) from the biphenyl/polychlorobiphenyl degrading organism Acidovorax sp. KKS102. KKSG9 possessed low sequence similarity but similar biochemical properties to zeta class GSTs. Functional analysis showed that the enzyme exhibits wider substrate specificity compared to most zeta class GSTs by reacting with 1-chloro-2,4-dinitrobenzene (CDNB), p-nitrobenzyl chloride (NBC), ethacrynic acid (EA), hydrogen peroxide, and cumene hydroperoxide. The enzyme also displayed dehalogenation function against dichloroacetate, permethrin, and dieldrin. The functional role of Tyr12 was also investigated by site-directed mutagenesis. The mutant (Y12C) displayed low catalytic activity and dehalogenation function against all the substrates when compared with the wild type. Kinetic analysis using NBC and GSH as substrates showed that the mutant (Y12C) displayed a higher affinity for NBC when compared with the wild type, however, no significant change in GSH affinity was observed. These findings suggest that the presence of tyrosine residue in the motif might represent an evolutionary trend toward improving the catalytic activity of the enzyme. The enzyme as well could be useful in the bioremediation of various types of organochlorine pollutants.
Two soap formulations, both containing 20% deet and one each containing permethrin at 0.5 and 1.0%, respectively, were applied to exposed arms and legs of volunteers as personal protection against outdoor human biting mosquitoes in six locations on Penang Island, Malaysia. The predominant mosquito species collected from these locations were Aedes albopictus, Mansonia uniformis, Culex gelidus, Anopheles lesteri and Armigeres subalbatus. Efficacy and residual effects up to 4 hours indicated good protection against these species. Reduction in mosquito landing-biting rates in treated groups ranged from 83.8 to 100.0%. At high densities, small percentages of Ma. uniformis and An. lesteri landed or bit on treated skin. Use of the soap formulations in terms of cost-effectiveness, safety and overall vector control strategy for some tropical diseases is discussed.
The state of Johore suffered a massive flood disaster from 19th December 2006 to 1st January and from 12th January to 19th February 2007. The possible upsurge of dengue was of foremost concern and led to efforts in increasing control activities. Anyone with history of high fever with at least two symptoms of severe headache, pain behind the eyes, muscles and joint paint, rashes and petechiae were notified as dengue. Active and passive case finding was initiated at all 371 evacuation centres as well through health facilities and hospitals through an active surveillance system. Presumptive larval survey was also carried together with control activities by 46 health teams. Data were collected using the format ‘Aktiviti harian kawalan denggi di kawasan pos banjir- Lampiran E‘ and ‘Laporan aktiviti harian kawalan denggi di pusat pemindahan banjir – Lampiran D2’. Dengue serology and blood film for malaria was sent for as well as vector species identification. A total of 594 dengue cases were reported for the period of 19th December 2006 till 19th February 2007, which was an increase in comparison to the 5-year median but less than that reported in year 2006. However only 14 (2.3%) cases were from flood affected areas. During the flood phase, a total of 5,929 inspections were carried out at the evacuation centres with Aedes Index (AI) of 1.86%, while the post flood period showed a lower index. However Breteau Index (BI) and Container Index (CI) were higher. Preventive fogging were carried out at the evacuation centres using adulticides, thermal fogging was carried out at 21,959 premises (40.04% of inspected premises) and 350.6 L adulticides (malathion, fenitrothion and permethrin) were used. Dengue was expected to increase during flood as a result of increase Aedes potential breeding sites. However with intensive and integrated control activities, Johore was able to minimize the impact of flood for vector-borne diseases as seen from the low cases reported in flood related areas. A special guidelines for surveillance and control was developed during this flood as a reference for future occurrences.
A glutathione S-transferase (GST) with a potential dehalogenation function against various organochlorine substrates was identified from a polychlorobiphenyl (PCB)-degrading organism, Acidovorax sp. KKS102. A homolog of the gene BphK (biphenyl upper pathway K), named BphK-KKS, was cloned, purified and biochemically characterized. Bioinformatic analysis indicated several conserved amino acids that participated in the catalytic activity of the enzyme, and site-directed mutagenesis of these conserved amino acids revealed their importance in the enzyme's catalytic activity. The wild-type and mutant (C10F, K107T and A180P) recombinant proteins displayed wider substrate specificity. The wild-type recombinant GST reacted towards 1-chloro-2,4-dinitrobenzene (CDNB), ethacrynic acid, hydrogen peroxide and cumene hydroperoxide. The mutated recombinant proteins, however, showed significant variation in specific activities towards the substrates. A combination of a molecular docking study and a chloride ion detection assay showed potential interaction with and a dechlorination function against 2-, 3- and 4-chlorobenzoates (metabolites generated during PCB biodegradation) in addition to some organochlorine pesticides (dichlorodiphenyltrichloroethane, endosulfan and permethrin). It was demonstrated that the behavior of the dechlorinating activities varied among the wild-type and mutant recombinant proteins. Kinetic studies (using CDNB and glutathione) showed that the kinetic parameters Km, Vmax, Kcat and Km/Kcat were all affected by the mutations. While C10F and A180P mutants displayed an increase in GST activity and the dechlorination function of the enzyme, the K107T mutant displayed variable results, suggesting a functional role of Lys107 in determining substrate specificity of the enzyme. These results demonstrated that the enzyme should be valuable in the bioremediation of metabolites generated during PCB biodegradation.
A small-scale trial was carried out in the Upper Kinabatangan district of Sabah, Malaysia, to determine the effect of using permethrin-impregnated bednets on malaria transmission. A total of 306 nylon bednets with cotton borders, impregnated at a dose estimated to have been 0.062 g permethrin/m2 of nylon netting, were distributed to 139 households in five villages. At the time of distributing bednets, mass drug administration with Fansidar plus primaquine was also administered to the human population to clear all parasitaemias due to Plasmodium falciparum Welch. In another village, for comparison, mass drug administration was the only intervention. After intervention measures in December 1984 and January 1985, the parasite rates in children declined in all villages during the first month, significantly more in the villages with impregnated bednets than in the control, thus proving that the nets had an impact on malaria. However, after about 2 months, parasite rates started to increase again. After 4-6 months, parasite rates in the villages with bednets approached the rate in the control village without nets. The increase in parasite rates was paralleled by a significant deterioration in the quality, physical condition and the degree of non-utilization of bednets. Entomological evaluation proved the efficacy of permethrin-impregnated nets for controlling Anopheles balabacensis Baisas and other anophelines. Bioassays (1 h exposure) of permethrin-impregnated bednets gave 100% mortality initially and 44-61% mortality after 85-106 days. Mosquito collections in treated bednets were significantly reduced for at least 217 days. The project failed to achieve prolonged suppression of malaria transmission for a combination of entomological, sociological and practical reasons which are discussed in relation to the objectives and implementation of future bednet studies.
Insecticide-treated mosquito nets were first put to practical use in the Western Pacific Region. Less than a decade after conducting workshops and other promotional activities, millions of people were protected by 1989. This occurred before the availability of commercially produced pretreated nets and before global funding for mass net distribution. This paper describes the sequence of steps leading to regional control success. The beginning stages in 1979 recognized that treating torn mosquito nets was a viable control option. Basic net treatment procedures were established by 1983 and workshops were held the next 2 years in China, Cambodia, Laos, Malaysia, Papua New Guinea, Philippines, Solomon Islands, Vanuatu, and Vietnam. Malaria staff became convinced of net benefits and were motivated to impart their knowledge to others. Village inhabitants soaked the nets in washbasins containing permethrin or deltamethrin solution, then dried them horizontally on mats. By the 1990s, the population protected by nets had appreciably increased, and regional malaria cases confirmed by microscopy were markedly reduced. This coincided with commercial interest to mass-produce pretreated mosquito nets for worldwide use.
BACKGROUND: Pediculiasis is treated aggressively in the United States, mainly with permethrin- and pyrethrin-containing pediculicides. Increasingly frequent anecdotal reports of treatment failure suggest the emergence of insecticidal resistance by these lice.
OBJECTIVE: To confirm or refute the susceptibility of head lice sampled in the United States to permethrin.
DESIGN: Survey. Head lice were removed from children residing where pediculicides are readily available and where such products are essentially unknown. Their survival was compared following exposure to residues of graded doses of permethrin in an in vitro bioassay.
SETTING: School children from Massachusetts, Idaho, and Sabah (Malaysian Borneo).
SUBJECTS: In the United States, 75 children aged 5 to 8 years. In Sabah, 59 boys aged 6 to 13 years. Virtually all sampled US children had previously been treated with pediculicides containing pyrethrins or permethrin; none of the Sabahan children were so exposed.
MAIN OUTCOME MEASURE: Survival of head lice exposed to permethrin.
RESULTS: Permethrin did not affect head lice sampled from chronically infested US children who had previously been treated for pediculiasis. The slope of the dose-response regression line for these lice did not differ significantly from zero (P = .66). This pediculicide immobilized lice sampled in Sabah. Mortality correlated closely with permethrin concentration (P = .008).
CONCLUSIONS: Head lice in the United States are less susceptible to permethrin than are those in Sabah. The pyrethroid susceptibility of the general population of head lice in the United States, however, remains poorly defined. Accordingly, these relatively safe over-the-counter preparations may remain the pediculicides of choice for newly recognized louse infestations.
The effect of permethrin impregnated bednets on Anopheles maculatus Theobald was studied in four villages in Pos Betau, Pahang, Malaysia from August 1990 to July 1992. Collections of mosquitos were carried out indoors and outdoors from 1900 to 0700 hours. All mosquitos were dissected for sporozoites and parity. In May 1991 two villages received bednets impregnated with permethrin at 0.5 g/m2 and two villages received placebo bednets. There was a significant difference in the sporozoite and parous rates between the treated and control villages after the distribution of bednets (p < 0.05). There was no significant difference in the bites/man/night of An. maculatus between the pre and post treatment periods in the control villages. However there was a significant difference in bites/man/night between pre and post treatment in the treated villages (p < 0.001).
The development of novel mosquito control tools is a key prerequisite to build effective and reliable Integrated Vector Management strategies. Here, we proposed a novel method using cigarette butts for the synthesis of Ag nanostructures toxic to young instars of the malaria vector Anopheles stephensi, chloroquine (CQ)-resistant malaria parasites Plasmodium falciparum and microbial pathogens. The non-target impact of these nanomaterials in the aquatic environment was evaluated testing them at sub-lethal doses on the predatory copepod Mesocyclops aspericornis. Cigarette butt-synthesized Ag nanostructures were characterized by UV-vis and FTIR spectroscopy, as well as by EDX, SEM and XRD analyses. Low doses of cigarette butt extracts (with and without tobacco) showed larvicidal and pupicidal toxicity on An. stephensi. The LC50 of cigarette butt-synthesized Ag nanostructures ranged from 4.505 ppm (I instar larvae) to 8.070 ppm (pupae) using smoked cigarette butts with tobacco, and from 3.571 (I instar larvae) to 6.143 ppm (pupae) using unsmoked cigarette butts without tobacco. Smoke toxicity experiments conducted against adults showed that unsmoked cigarette butts-based coils led to mortality comparable to permethrin-based positive control (84.2 and 91.2%, respectively). A single treatment with cigarette butts extracts and Ag nanostructures significantly reduced egg hatchability of An. stephensi. Furthermore, the antiplasmodial activity of cigarette butt extracts (with and without tobacco) and synthesized Ag nanostructures was evaluated against CQ-resistant (CQ-r) and CQ-sensitive (CQ-s) strains of P. falciparum. The lowest IC50 values were achieved by cigarette butt extracts without tobacco, they were 54.63 μg/ml (CQ-s) and 63.26 μg/ml (CQ-r); while Ag nanostructure IC50 values were 72.13 μg/ml (CQ-s) and 77.33 μg/ml (CQ-r). In MIC assays, low doses of the Ag nanostructures inhibited the growth of Bacillus subtilis, Klebsiella pneumoniae and Salmonella typhi. Finally, the predation efficiency of copepod M. aspericornis towards larvae of An. stephensi did not decrease in a nanoparticle-contaminated environment, if compared to control predation assays. Overall, the present research would suggest that an abundant hazardous waste, such as cigarette butts, can be turned to an important resource for nanosynthesis of highly effective antiplasmodials and insecticides.