Can vector control play a useful supplementary role against bancroftian filariasis?
A single campaign of mass treatment for bancroftian filariasis with diethylcarbamazine (DEC) in Makunduchi, a town in Zanzibar, United Republic of Tanzania, combined with elimination of mosquito breeding in pit latrines with polystyrene beads was followed by a progressive decline over a 5-year period in the microfilarial rate from 49% to 3%. Evidence that vector control had contributed to this long-term decline was obtained by comparison with another town, Moga, where a DEC campaign was used without vector control and where resurgence of microfilariae could be observed 3-6 years after the campaign. In Zanzibar town, treatment of 3844 wet pit latrines and cesspits with polystyrene beads reduced the adult mosquito population in houses by about 65%. Supplementary treatment of open drains and marshes with Bacillus sphaericus produced little or no additional reduction compared to a sector of the town where only pit treatment with polystyrene was carried out. The cost and effort of achieving the 65% reduction in mosquito population could hardly be justified for its impact on filariasis alone, but its noticeable impact on biting nuisance might help to gain community support for an integrated programme. (+info)
Monitoring community response to malaria control using insecticide-impregnated bed nets, curtains and residual spray at Nsukka, Nigeria.
A project testing the efficacy of insecticide (permethrin)-impregnated bed nets, compared with impregnated door and window curtains, residual house spraying, and a control group was implemented in 12 village clusters in the Nsukka Local Government Area of Enugu State, Nigeria, using epidemiologic and entomologic indicators. The appropriate materials and services were given free to all families. During the first year of study, three monitoring exercises were carried out in a random selection of homes where children under 5 years of age resided. Information was collected on perceived effectiveness of the interventions, condition of nets and curtains, reasons for not sleeping under nets, and recall of steps required in caring for nets and curtains. Bed nets were perceived as more effective in reducing mosquito bites compared with the two other interventions. At the last monitoring period, which occurred a few weeks before a re-impregnation exercise, respondents also perceived bed nets to be most effective in preventing malaria. These findings coincided with epidemiologic evidence. Curtains, especially those at doors, were more likely to be torn and dirty than bed nets. Although holes would not reduce the effectiveness of the insecticide, they could reduce the 'beauty' of the curtains, a perceived benefit that initially attracted villagers to both curtains and nets. Bed net owners reported significantly less frequent use of other mosquito control measures in their homes than did members of the other groups. Finally, bed net users demonstrated increased knowledge of use and care steps than did those with curtains. These findings suggested a high level of social acceptability of bed nets, and point to the need to test their acceptability further under conditions where people would pay for nets and communities would manage distribution and re-impregnation systems. (+info)
Insecticide-treated nets and treatment service: a trial using public and private sector channels in rural United Republic of Tanzania.
The Rotary Net Initiative, implemented in Kilombero District, southern United Republic of Tanzania, allowed us to explore different sales channels for the distribution of insecticide-treated nets (ITNs) and the insecticide treatment service in a rural area of very high malaria transmission. Several types of ITNs were promoted and sold through different channels in the public and private sector, i.e. hospital pharmacy, mother and child health (MCH) clinic, net committee, village health workers and retail shops. The ITNs were sold for US$ 5.0-9.2, with profit margins of 9-16%. Net treatment cost US$ 0.33, with commission fees of 75%. Net transport and treatment were partially subsidized. Some outlets established their own fund by ITN sales. Sales of nets and treatments were seasonal, and certain net types were preferred. Demand for insecticide treatment was generally low. Changes in net coverage were assessed in two villages. A range of outlet features were compared qualitatively. Our experience supports suggestions that ITN technology should be delivered through MCH care services and demonstrates that specific promotion and innovation are necessary to achieve substantial net treatment levels. A large-scale ITN project in the same area and other ITN studies should lead to better understanding of ITN implementation at the population level. (+info)
Control of malaria vectors: cost analysis in a province of northern Vietnam.
The cost of permethrin-treated bednets (50% EC; 0.2 g/m2, 2 rounds per year) was compared to the cost of residual spraying with lambdacyhalothrin 10% WP (0.03 g/m2, once yearly) in Hoa Binh, a mountainous province in northern Vietnam. Calculations of the amounts of insecticides needed were based on national guidelines, on data from a cross-sectional survey and on district activity reports. The actual cost of insecticide required per person per year was lower for impregnation (US$ 0.26) than for spraying (US$ 0.36), but the difference was smaller than expected. The total cost for impregnated bednets per person per year amounted to US$ 0.90 compared to USS 0.47 for spraying. The determining factor was the cost of the net, amounting to US$ 0.58 per person per year, assuming a 5-year life of the net. Other material (excluding nets), labour and transport combined, accounted for only 17% of the impregnation cost and 23% of spraying expenses. However, for the National Malaria Control Programme of Vietnam, the cost per person per year for impregnated bednets amounted to US$ 0.32 only, because the vast majority of nets are bought by the population. For spraying, the programme had to bear the entire cost. (+info)
A new strategy for treating nets. Part 1: formulation and dosage.
The conventional dosages of pyrethroid insecticides on mosquito nets assume that nets will be retreated at 6-12 month intervals. However, dosage should be related to washing of nets; if nets are only washed once or twice a year, their dosage requirements will be different to those which are washed fortnightly. A 'low-dose, frequent-wash' retreatment system might be technically more appropriate and more affordable where nets are washed frequently, as they are in Dar es Salaam. Moreover, for use as a domestic insecticide, water-based formulations of pyrethroid are preferable to the more commonly used emulsifiable concentrates (ECs). This paper reports laboratory evaluations of three formulations (ECs, Flowable, CS) of three pyrethroids (deltamethrin, lambdacyhalothrin, permethrin). Insecticidal activity was tested using serial bioassays at a range of dosages using Anopheles gambiae. The water-based formulations were no less effective than the ECs, even at the lowest dosages. Nets treated with 3 mg/m2 and then repeatedly washed and retreated after each wash with either 3 mg/m2 or 1 mg/m2 were subjected to gas chromatography analysis. This showed that the amounts of pyrethroid in the nets accumulated rapidly over the first few wash-retreatment cycles and then remained fairly stable over subsequent cycles. These nets gave consistently high bioassay mortalities throughout the experiment, while the mortality declined rapidly after several washes with the nets that were treated at 3 mg/m2 but not retreated. Experimental huts were used to compare the effectiveness of these 2 net retreatment regimes and nets which were not retreated. All nets caused high mortality rates amongst Anopheles females, but had negligible effects on culicines; either in killing them or in preventing feeding. Therefore use of a high 'loading' dose for initial treatment with lower 'maintenance' doses for retreatment may be preferable to ensure that net users promptly perceive the benefits of the insecticide against culicines. (+info)
A new strategy for treating nets. Part 2: users' perceptions of efficacy and washing practices and their implications for insecticide dosage.
The conventional way to treat a mosquito net with pyrethroid insecticide is to apply a standard dosage every 6-12 months, and to avoid washing the net until just before retreatment. In some places, nets are normally washed much more often than this, and it may then be more appropriate to apply smaller amounts of insecticide after each wash. The choice of strategy must take into account not only biological effectiveness, but also users' perceptions of this effectiveness and their net-washing habits. We used focus groups to compare users' responses to nets treated with different dosages and chemicals. One hundred current net users in urban Dares-Salaam were each given a net that had been pretreated either with permethrin (200 or 500 mg/m2), or with lambdacyhalothrin (3 or 15 mg/m2), or with water. Neither participants nor investigators knew which group had received which treatment. Focus group discussions were held after 2, 8 and 12 weeks. Participants greatly preferred treated nets. Low doses were perceived to be less effective, especially after 8 and 12 weeks. After 12 weeks most participants had washed their nets, despite requests to the contrary Dirty nets were regarded as unhealthy and socially unacceptable. Few participants experienced side-effects or expressed fears about the safety of treatment. We conclude that asking people to refrain from washing their nets is unrealistic. A 'low-dose frequent-treatment' strategy of insecticide application may be more appropriate in the long run. At first, however, low doses give perceptibly inferior protection. An initial high (loading) dose, followed by frequent lower (maintenance) dosages, might solve this problem. (+info)
Rebound mortality and the cost-effectiveness of malaria control: potential impact of increased mortality in late childhood following the introduction of insecticide treated nets.
The efficacy and relative cost-effectiveness of insecticide-treated nets (ITNs) for the control of malaria in children under 5 years of age have recently been demonstrated by several large-scale trials. However, it has been suggested that long-term use of ITNs in areas of high transmission could lead to mortality rebound in later childhood, which would reduce the cost-effectiveness of the intervention, and at the extreme could lead to negative overall effects. A model is presented in which the cost and disability adjusted life years (DALYs) per child aged 1-119 months were estimated for a sub-Saharan African population with and without an ITN intervention. The rebound rate, defined as the percentage increase in age-specific all-cause mortality and malaria specific-morbidity, was varied to estimate the threshold at which the intervention was no longer cost-effective. Rebound was considered over two possible age ranges: 5-9 years and 3-6 years. With mortality and morbidity reductions due to ITNs in children aged 1-59 months and rebound in the 5-9 years age class, one could be reasonably certain that the cost per DALY averted is below $150 up to a rebound rate of 39%. Up to an 84% rebound rate it is highly likely that the intervention will be DALY-averting, that is the DALYs averted by the intervetion outweigh DALYs incurred through rebound effects. These thresholds are sensitive to the age range over which reductions and rebound in morbidity and mortality occur. With reductions confined to children aged 1-35 months and rebound in the 3-6 years age class, the cost per DALY is highly likely to fall below $150 only up to a 2.5% rebound rate, and with a rate in excess of 11% one can no longer be reasonably certain that the intervention is DALY-averting. These rates apply to the whole population. If there is no rebound amongst children who did not comply with the intervention, the actual increases in morbidity and mortality required to reach these thresholds amongst compliers would be much higher. The age range over which rebound occurs is a critical determinant of the thresholds at which one can no longer be reasonably certain that ITNs remain cost-effective in the long term. Based on empirical estimates of age-specific malaria mortality in sub-Saharan Africa, it appears unlikely that this threshold rate would be reached if rebound occurs over the 5-9 years age range. By contrast, if rebound occurs over the ages of 3-6 years, the increase in mortality rates required to reach this threshold falls within the observed range of malaria-specific mortality rates for this age group. It is essential that long-term surveillance is included as part of ITN interventions, with particular attention to the age range over which rebound may occur. (+info)
Identification of two species within the Anopheles minimus complex in northern Vietnam and their behavioural divergences.
Elucidating the complex taxonomic status of the major malaria vector taxa and characterising the individual species within each complex is important for understanding the complexity of the vector system in the south-east Asian region and will allow to estimate the impact of vector control measures. This applies to countries such as Laos, Cambodia and Vietnam that spend about 60% of their malaria control budget on implementing vector control activities. We used isozyme electrophoresis to clarify the Anopheles minimus s.l. species composition in northern Vietnam and identify behavioural divergences of individual species. Using different collection methods, adult mosquitoes were caught at monthly intervals from June to November 1995 in four villages. An. minimus s.l. could be distinguished from closely related species, An. aconitus and An. jeyporiensis, at the Octanol dehydrogenase (Odh) enzyme locus. Significant positive Fis values gave clear evidence of nonrandom mating within the An. minimus s.l. population. The highest heterozygote deficiency was observed at locus Odh, which was diagnostic for 2 sympatric An. minimus species in Vietnam similar to the An. minimus A and C species known from Thailand. We found no evidence for restricted gene flow between monthly samples, villages, or collection methods in either of the two An. minimus species. They occurred in sympatry, but in different proportions depending on the collection site, and had dissimilar resting and biting behaviours. Thus a vector control strategy will have a nonuniform effect on the various components of this diverse vector system. (+info)