Modified veranda-trap hut for improved evaluation of vector control interventions.

Experimental huts with veranda traps have been used in Tanzania since 1963 for the study of residual insecticides for use with insecticide-treated nets and indoor residual spraying. Mosquitoes are allowed unrestricted entry through the eaves to facilitate the collection of an estimable proportion of mosquitoes that attempt to exit through the eave gaps, which are left open on two sides of the hut. This study was designed to validate the use of eave baffles to funnel entry and to prevent mosquito escape, and to determine biting times of Anopheles arabiensis (Patton) (Diptera: Culicidae). Anopheles arabiensis and Culex quinquefasciatus (Say) (Diptera: Culicidae) were released into the room at 20.30 hours and collected the following morning from veranda traps, window traps and the room. Centers for Disease Control light traps hung overnight next to volunteers were emptied every 2 h to determine peak biting times. A total of 55% of An. arabiensis were trapped before 22.30 hours and the highest peak in 'biting' was recorded during 18.30-20.30 hours. Of the released An. arabiensis that exited into veranda traps, 7% were captured in veranda traps entered through baffles and 93% were captured in traps entered through unmodified eaves. When veranda screens were left open to allow for escape outdoors, recapture rates were 68% for huts with eave baffles and 39% for huts with unmodified eaves. The comparison of open eaves with baffled eaves validated the assumption that in huts of the traditional non-baffled design, 50% of mosquitoes escape through open eaves. Eave baffles succeeded in reducing the potential for mosquito exit and produced more precise estimates of effect.

Evaluation of indoor residual spraying with the pyrrole insecticide chlorfenapyr against pyrethroid-susceptible Anopheles arabiensis and pyrethroid-resistant Culex quinquefasciatus mosquitoes.

Chlorfenapyr is a pyrrole insecticide with a unique non-neurological mode of action. Laboratory bioassays of chlorfenapyr comparing the mortality of pyrethroid-susceptible and -resistant Anopheles gambiae s.s. and Culex quinquefasciatus mosquitoes indicated that operational cross-resistance is unlikely to occur (resistance ratio ranged between 0 and 2.1). Three trials of chlorfenapyr indoor residual spraying were undertaken in experimental huts in an area of rice irrigation in northern Tanzania that supports breeding of A. arabiensis. Daily mosquito collections were undertaken to assess product performance primarily in terms of mortality. In the second trial, 250mg/m(2) and 500mg/m(2) chlorfenapyr were tested for residual efficacy over 6 months. Both dosages killed 54% of C. quinquefasciatus, whilst for A. arabiensis 250mg/m(2) killed 48% compared with 41% for 500mg/m(2); mortality was as high at the end of the trial as at the beginning. In the third trial, 250mg/m(2) chlorfenapyr was compared with the pyrethroid alpha-cypermethrin dosed at 30mg/m(2). Chlorfenapyr performance was equivalent to the pyrethroid against A. arabiensis, with both insecticides killing 50% of mosquitoes. Chlorfenapyr killed a significantly higher proportion of pyrethroid-resistant C. quinquefasciatus (56%) compared with alpha-cypermethrin (17%). Chlorfenapyr has the potential to be an important addition to the limited arsenal of public health insecticides for indoor residual control of A. arabiensis and pyrethroid-resistant species of mosquito.

Behavioural and insecticidal effects of organophosphate-, carbamate- and pyrethroid-treated mosquito nets against African malaria vectors.

Three insecticides - the pyrethroid deltamethrin, the carbamate carbosulfan and the organophosphate chlorpyrifos-methyl - were tested on mosquito nets in experimental huts to determine their potential for introduction as malaria control measures. Their behavioural effects and efficacy were examined in Anopheles gambiae Giles s.s. (Diptera: Culicidae) and Anopheles funestus Giles s.s. in Muheza, Tanzania, and in Anopheles arabiensis Patton and Culex quinquefasciatus Say in Moshi, Tanzania. A standardized dosage of 25 mg/m(2) plus high dosages of carbosulfan (50 mg/m(2), 100 mg/m(2) and 200 mg/m(2)) and chlorpyrifos-methyl (100 mg/m(2)) were used to compare the three types of insecticide. At 25 mg/m(2), the rank order of the insecticides for insecticide-induced mortality in wild An. gambiae and An. funestus was, respectively, carbosulfan (88%, 86%) > deltamethrin (79%, 78%) > chlorpyrifos-methyl (35%, 53%). The rank order of the insecticides for blood-feeding inhibition (reduction in the number of blood-fed mosquitoes compared with control) in wild An. gambiae and An. funestus was deltamethrin > chlorpyrifos-methyl > carbosulfan. Carbosulfan was particularly toxic to endophilic anophelines at 200 mg/m(2), killing 100% of An. gambiae and 98% of An. funestus that entered the huts. It was less effective against the more exophilic An. arabiensis (67% mortality) and carbamate-resistant Cx quinquefasciatus (36% mortality). Carbosulfan deterred anophelines from entering huts, but did not deter carbamate-resistant Cx quinquefasciatus. Deltamethrin reduced the proportion of insects engaged in blood-feeding, probably as a consequence of contact irritancy, whereas carbosulfan seemed to provide personal protection through deterred entry or perhaps a spatial repellent action. Any deployment of carbosulfan as an individual treatment on nets should be carried out on a large scale to reduce the risk of diverting mosquitoes to unprotected individuals. Chlorpyrifos-methyl was inferior to deltamethrin in terms of mortality and blood-feeding inhibition and would be better deployed on a net in combination with a pyrethroid to control insecticide-resistant mosquitoes.

Is K-O Tab 1-2-3((R)) long lasting on non-polyester mosquito nets?

Many societies use locally sourced mosquito nets made from a variety of materials. For protecting against malaria these require regular re-treatment with insecticide. K-O Tab 1-2-3 is a 'dip-it-yourself' long-lasting formulation with time-limited interim recommendation from WHO for treatment of washed white and coloured polyester nets for up to 15 washes. To determine wash-resistance on different fabrics, nets made of polyester, polyethylene, cotton or nylon were treated with K-O Tab 1-2-3 and washed up to 20 times using standard WHO washing procedures. Efficacy was assessed using cone and cylinder bioassays and tunnel tests, and deltamethrin content using high-pressure liquid chromatography. Polyethylene and cotton nets treated with K-O Tab 1-2-3 and washed 20 times achieved the WHO threshold of >80% mortality in tunnel tests. Polyethylene matched the performance of polyester in all bioassays in contrast to cotton and nylon which produced low mortality and knock-down in cone and cylinder bioassays. After 20 washes 16.5% of the loading dose of deltamethrin remained on the polyester nets compared with 28.7% on polyethylene, 38.9% on cotton and 2.2% on nylon. Cotton nets retained a high concentration of insecticide but the relatively poor performance in terms of knock-down and mortality suggest most insecticide is bound within the cotton fibres rather than on the surface. K-O Tab 1-2-3 renders insecticide wash fast on polyethylene nets, less so on cotton and nylon. Nets made from polyethylene can be treated in the home to render the insecticide long lasting.

Comparative efficacies of permethrin-, deltamethrin- and alpha-cypermethrin-treated nets, against Anopheles arabiensis and Culex quinquefasciatus in northern Tanzania.

Mosquito nets treated with permethrin, deltamethrin or alpha-cypermethrin at 25 mg/m(2) were evaluated in experimental huts in an area of rice irrigation near Moshi, in northern Tanzania. The nets were deliberately holed to resemble worn nets. The nets treated with permethrin offered the highest personal protection against Anopheles arabiensis (61.6% reduction in fed mosquitoes) and Culex quinquefasciatus (25.0%). Deltamethrin and alpha-cypermethrin provided lower personal protection against An. arabiensis (46.4% and 45.6%, respectively) and no such protection against Cx. quinquefasciatus. Permethrin performed poorly in terms of mosquito mortality, however, killing only 15.2% of the An. arabiensis and 9.2% of the Cx. quinquefasciatus exposed to the nets treated with this pyrethroid (after correcting for control mortality). The alpha-cypermethrin and deltamethrin performed marginally better, with respective mortalities of 32.8% and 33.0% for An. arabiensis and 19.4% and 18.9% for Cx quinquefasciatus. The poor killing effect of permethrin was confirmed in a second trial where a commercial, long-lasting insecticidal net based on this pyrethroid (Olyset) produced low mortalities in both An. arabiensis (11.8%) and Cx. quinquefasciatus (3.6%). Anopheles arabiensis survivors collected from the verandahs of the experimental huts and tested on 0.75%-permethrin and 0.05%-deltamethrin papers, in World Health Organization susceptibility kits, showed mortalities of 96% and 100%, respectively. The continued use of permethrin-treated nets is recommended for personal protection against An. arabiensis. In control programmes that aim to interrupt transmission of pathogens by mosquitoes and/or manage pyrethroid resistance in such vectors, a combination of a pyrethroid and another insecticide with greater killing effect should be considered.

Multi-country field trials comparing wash-resistance of PermaNet and conventional insecticide-treated nets against anopheline and culicine mosquitoes.

Insecticide-treated bednets (ITNs) are commonly used as a means of personal protection from malaria transmission by anopheline mosquitoes (Diptera: Culicidae). Long-lasting insecticidal nets (LLINs) have special treatments intended to remain effective after many washes. The present trials assessed the efficacy and wash-resistance of several production batches of PermaNet (polyester net coated with polymer resin containing pyrethroid insecticide deltamethrin 55 mg ai/m2) against malaria vectors in Pakistan, Iran and Tanzania compared to ITNs conventionally treated with alphacypermethrin 15 or 20 mg ai/m2, or deltamethrin 25 or 50 mg ai/m2. Insecticidal efficacy of the nets before and after repeated washing (using W.H.O. recommended and traditional local washing procedures) was monitored through contact bioassays with Anopheles and by experimental hut and outdoor platform tests. Local washing regimes gradually reduced the insecticidal efficacy of conventionally treated nets, but they were not exhausted, even after 21 washes. Using a more rigorous laboratory washing method, insecticide was more readily stripped from conventionally treated nets. PermaNet retained high efficacy after 21 washes, giving more than 97% mortality of Anopheles in contact bioassays with 3-min exposure. Using the more sensitive bioassay criterion of 'median time to knockdown', PermaNet showed no loss of insecticidal activity against Anopheles after washing repeatedly in 2 out of 6 trials; whereas in a further three trials knockdown activity of PermaNet and conventional ITNs declined at comparable rates. Higher mortality levels of Anopheles in contact bioassays did not always translate to superiority in experimental hut or enclosed platform trials. In only one of four comparative field trials did PermaNet out-perform conventional ITNs after washing: this was in the trial of PermaNet 2.0--the product with improved quality assurance. Because PermaNet and conventionally treated nets were both quite tolerant of local washing procedures, it is important in field trials to compare LLINs with conventional ITNs washed an equivalent number of times. Our comparison of PermaNet 2.0 against conventionally treated deltamethrin nets (CTDN) in Pakistan demonstrated superior performance of the LLIN after 20 washes in phase I and phase II bioassays, and this was corroborated by chemical assays of residual deltamethrin. Although PermaNet 2.0 has received WHOPES interim recommendation for malaria control purposes, its performance should be monitored in everyday use throughout its lifespan in various cultural settings to assess its durability and long-term effectiveness for malaria prevention and control. As many millions of conventionally treated nets are already in routine use, and these will require regular re-treatment, programme strategies should be careful to preserve the effectiveness of ITNS before and after establishing the reliability of LLINs in long-term use.

Resistance of Plasmodium falciparum malaria to chloroquine is widespread in eastern Afghanistan.

After two decades of war and conflict in Afghanistan, the public-health system is in disarray and malaria has re-emerged as a major disease, with Plasmodium falciparum malaria becoming increasingly common. The limited healthcare services that are available are mainly delivered by non-governmental organizations in collaboration with the Ministry of Health. Although chloroquine (CQ) remains the official first-line treatment against P. falciparum malaria, there is little information on the severity or distribution of resistance to this drug in Afghanistan. In-vivo surveys, co-ordinated by the Malaria Reference Centre in Jalalabad, were therefore performed to determine the frequency and grades of CQ resistance in the three eastern provinces of Kunar, Nangarhar and Laghman. Of the 142 cases enrolled in the study, only 47 (33%) were sensitive. Most of the cases (55%) showed RI resistance but RII/RIII resistance was not uncommon (11%). The prevalence of resistance appeared similar in children and adults, in males and females, and in each of the three provinces investigated. Gametocyte carriage post-treatment was elevated in the resistant cases. As in neighbouring Pakistan, the resurgence of P. falciparum in Afghanistan is probably associated with the transmission and spread of chloroquine-resistant strains. The first-line therapy used against P. falciparum malaria must be changed in order to reverse this trend.

Self-protection from malaria vectors in Pakistan: an evaluation of popular existing methods and appropriate new techniques in Afghan refugee communities.

Experimental huts were used to measure the impact of several techniques for self-protection from malaria vectors in Pakistan. An electric fan, pyrethrum coils, untreated curtains, pyrethroid-vaporizing mats and permethrin-impregnated curtains reduced the total catches of blood-fed Anopheles stephensi by 27%, 36%, 47%, 56% and 65%, respectively. The most marked effect of all the interventions was in reducing the numbers of mosquitoes entering the huts, although all the techniques, except for the untreated curtain, also reduced the proportion of mosquitoes inside the hut which fed. Although the trends seen were similar for both anopheline (all An. stephensi) and culicine mosquitoes, they were more pronounced in the culicines. Social surveys were conducted on current self-protection practices. The social and economic constraints associated with each of the various techniques are discussed. All the strategies were shown to offer a degree of protection and their use should be encouraged. Impregnated curtains seem especially promising. Pyrethroid-impregnated bednets have been widely promoted in eastern Afghanistan since 1991 and have the advantage of providing protection when people sleep outside during the summer. However, surveys show that some owners stop using their nets in late autumn, despite the continued risk of malaria. People should be encouraged to use their bednets as impregnated curtains rather than putting them into storage.

Effects of ivermectin residues in sheep dung on the development and survival of the bushfly, Musca vetustissima Walker and a scarabaeine dung beetle, Euoniticellus fulvus Goeze.

During produced by sheep for up to 1 week post-treatment (drenching) with ivermectin caused significant mortality to newly emerged larvae of the bushfly Musca vetustissima. Dung from sheep drenched with a mixture of levamisole and oxfendazole also resulted in larval mortality, but here the effect was limited to the first 48 h after treatment. Flies reared through to the adult stage on dung collected up to 32 days post-drenching were tested for evidence of fluctuating asymmetry, which is an indicator of developmental stress. None was found for either drench treatment, although there was evidence that ivermectin residues directly affected wing size. The introduced dung beetle, Euoniticellus fulvus was also found to be sensitive to ivermectin residues in sheep dung. Dung produced during the first day after drenching caused mortality among newly emerged beetles and delayed the reproductive development of survivors. However, beetles in which ovarian development was impaired regained their reproductive capacity following transfer to nontoxic dung. Day 1 dung caused no mortality among sexually mature beetles, although there was a significant reduction in their fecundity. Dung collected from 2 to 10 days post-drenching had no detectable effects on either the survival or reproductive development of adult beetles, regardless of age. Residues in dung collected 1-2 days post-drenching caused 100% mortality in beetle larvae, but by Day 5 there was no evidence of acute toxicity. These findings indicate that insects feeding on the dung of ivermectin-treated sheep display adverse effects similar in range to those reported for cattle dung. However, their duration is much more transient, owing probably to differences in drug formulation and route of administration.