Insecticide-treated bednet use, anaemia, and malaria parasitaemia in Blantyre District, Malawi

OBJECTIVE: To evaluate the use of insecticide-treated bednets and the effectiveness of social marketing for their distribution. METHODS: Systematic cluster sample survey of 1080 households in 36 census enumeration areas across Blantyre district, Malawi, in February 2000. RESULTS: A total of 672 households had one or more children under 5. Bednet ownership was low (20.5% of households) overall, and significantly lower in rural areas than urban areas (6.4 vs. 29.8%, P=0.001). Only 3.3% of rural children under 5 had slept under a net the previous night, compared with 24.0% of urban children (P < 0.001). When asked why they did not own a net, nearly all (94.9%) caretakers in households without nets stated they had no money to buy them. In multivariate statistical models that controlled for the influence of house structure, urban vs. rural location, gender of the head of household, and the primary caretaker's education, rural children under 5 in households without nets experienced a statistically significant higher prevalence of malaria parasitaemia [RR (risk ratio) 4.9, 95% CI (confidence interval) 2.3-10.5] than children in households with at least one bednet. This was also true for urban children under 5 (RR 2.1, 95% CI 1.0-4.2, P=0.04). CONCLUSION: Social marketing approaches to promoting insecticide-treated nets in Blantyre District may have produced measurable health benefits for children in those households in which residents bought and used the products. Market-based approaches may take years to achieve high levels of coverage and may exaggerate inequities between urban and rural populations.     

Socially marketed insecticide-treated nets improve malaria and anaemia in pregnancy in southern Tanzania

OBJECTIVES: To study the uptake of socially marketed insecticide-treated nets (ITNs) and their impact on malaria and anaemia in pregnancy; and to report on a discount voucher system which aimed to increase coverage in pregnancy. METHODS: A 12-month cross-sectional study of women in the second or third trimester of pregnancy. ITN use and other factors were assessed by questionnaire and a blood sample taken for malaria parasitaemia and anaemia. 'Non-users' of ITNs included both women not using any net and women using untreated nets. RESULTS: Fifty three per cent of pregnant women used ITNs. Women aged 15-19, primigravidae, unmarried women, and those with no access to cash had the lowest ITN use. Fewer ITN users were positive for malaria than ITN non-users (25 vs. 33%: P=0.06), and the protective efficacy (PE) for parasitaemia was 23% (CI 2-41). Multiparous ITN users had a twofold decrease in parasite density compared with multiparous non-ITN users (625 parasites/microl vs. 1173 parasited/microl: P=0.01). Fewer ITN users were anaemic (Hb < 11 g/dl) than ITN non-users (72 vs. 82%: P=0.01). ITNs had a PE of 12% (CI 2-21) against mild anaemia and a PE of 38% (CI 4-60) against severe anaemia (Hb < 8 g/dl). There was a trend in the prevalence of severe, mild and no anaemia, and of high density, low density and no malaria infection by ITN status. Recently treated nets were most effective at preventing malaria and anaemia (prevalence of mild anaemia was 68% compared with 82% for those without nets (P=0.002); prevalence of malaria was 22% compared with 33% for those without nets (P=0.02). Knowledge and reported use of the discount voucher system were low. Further qualitative research is ongoing. CONCLUSIONS: A modest impact of ITNs on pregnancy malaria and anaemia was shown in our high malaria transmission setting. The development of ITN programmes for malaria control should include pregnant women as a specific target group.     

Comparison of deltamethrin tablet formulation with liquid deltamethrin and permethrin for bednet treatment in The Gambia

The study aim was to compare three formulations, tablet deltamethrin, liquid deltamethrin and liquid permethrin, for their impact on vector behaviour and persistence. Product acceptance, perceived side-effects and user's perceptions of effectiveness were also investigated. At the beginning of the 1998 rainy season, 255 nets in a Gambian village were dipped in one of the three insecticides. Chemical residue analysis immediately after dipping showed that the target doses were reached for the liquid insecticides, but tablet deltamethrin deposited significantly less. Insecticide persistence at 5 months, however, was highest for the tablet formulation. Susceptibility tests established that Anophelines in this area were sensitive to both insecticides. All three formulations appeared effective as very few live Anophelines, or other mosquitoes, were caught under the treated nets. This conclusion was supported by the bioassay data with both deltamethrin formulations giving over 90% mortality soon after dipping and at 3 months, and at 5 months 70.8 and 79.6% were obtained for deltametrin liquid and tablet, respectively. Permethrin appeared less effective at all times (72.4, 86.8, 59.0%). There were no serious side-effects reported by the villagers following dipping. All three treatments were perceived as effective by the majority (92%) of users and most (93%) wanted to use the insecticide again. Deltamethrin tablets thus appear as good as permethrin for treating bednets in The Gambia. In addition, a tablet formulation is considerable easier to pack and distribute.     

Malaria in camps for internally-displaced persons in Uganda: evaluation of an insecticide-treated bednet distribution programme

Malaria is a key health problem among displaced populations in malaria-endemic areas. Mass distribution of insecticide-treated bednets (ITN) to prevent malaria is often carried out in complex emergencies, but there are few data on the outcome or operational effectiveness of such programmes. In June 2001, Medecins Sans Frontieres completed a mass distribution of ITNs (Permanet) to internally displaced persons in Bundibugyo, southwest Uganda, distributing one to four nets per household, and aiming to provide coverage for all residents. In July 2002, we did a cross-sectional survey using three-stage cluster sampling to evaluate the programme. A total of 1245 individuals from 835 households were interviewed. An ITN was present in 75.6% (95% CI 72.7-78.5) of the households, but only 56.5% (95% CI 52.3-60.4) of individuals were sleeping under an ITN, and nets were often damaged. The prevalence of malarial parasitaemia was 11.2% (95% CI 9.4-13.0), and was significantly lower in ITN users compared to non-users (9.2% vs. 13.8%, relative risk [RR] 0.63, 95% CI 0.46-0.87); ITNs with severe damage remained effective (RR for severely damaged net 0.58, 95% CI 0.35-0.98). There was no significant difference in haemoglobin concentration between ITN users and non-users.     

Importance and prevention of malaria in pregnancy

Malaria in pregnancy is one of the most important preventable causes of low birthweight deliveries worldwide. It is also a major cause of severe maternal anaemia contributing to maternal mortality. It is estimated that 40% of the world's pregnant women are exposed to malaria infection during pregnancy. The clinical features of Plasmodium falciparum malaria in pregnancy depend to a large extent on the immune status of the woman, which in turn is determined by her previous exposure to malaria. In pregnant women with little or no pre-existing immunity, such as women from non-endemic areas or travellers to malarious areas, infection is associated with high risks of severe disease with maternal and perinatal mortality. Women are at particular risk of cerebral malaria, hypoglycaemia, pulmonary oedema and severe haemolytic anaemia. Fetal and perinatal loss has been documented to be as high as 60-70% in non-immune women with malaria. Adults who are long-term residents of areas of moderate or high malaria transmission, including large parts of sub-Saharan Africa, usually have a high level of immunity to malaria. Infection is frequently asymptomatic and severe disease is uncommon. During pregnancy this immunity to malaria is altered. Infection is still frequently asymptomatic, so may go unsuspected and undetected, but is associated with placental parasitization. Malaria in pregnancy is a common cause of severe maternal anaemia and low birthweight babies, these complications being more common in primigravidae than multigravidae. Preventative strategies include regular chemoprophylaxis, intermittent preventative treatment with antimalarials and insecticide-treated bednets.     

The effects of untreated bednets on malaria infection and morbidity on the Kenyan coast

A study was conducted in order to determine whether children that slept under untreated bednets were protected against both malaria infection and clinical disease compared with children not sleeping under bednets. The study was conducted in Kilifi District, Kenya, during the malaria season (June-August, 2000) and involved 416 children aged < or = 10 years. Data collected from a cross-sectional survey showed evidence of protection against malaria infection among children sleeping under untreated bednets in good condition compared with those not using nets (adjusted odds ratio [AOR] = 0.4, 95% CI 0.22-0.72, P = 0.002). There was no evidence of a protective effect against infection when comparing those that used untreated bednets that were worn and those not using nets (AOR = 0.75, 95% CI 0.34-1.63, P = 0.47). When these same children were followed-up during the malaria season, there was evidence of a lower rate of clinical malaria among those that used untreated nets in good condition (adjusted incidence rate ratio = 0.65, 95% CI 0.45-0.94, P = 0.022), while the rate of clinical malaria among those that used untreated bednets that were worn was similar to that of those that did not use bednets. In the face of persistent failure of communities to take up net retreatment, there is hope that untreated nets will offer some protection against malaria infection and disease compared with not using nets at all.     

两种杀虫剂浸泡蚊帐现场杀灭效果观察

目的在苏丹维和区观察比较奋斗呐和大灭杀虫剂浸泡蚊帐对蚊、蝇和其他昆虫的现场杀灭效果。方法选用奋斗呐(30mg.ai/m2)和大灭(20mg.ai/m2)浸泡军用蚊帐,检测对蚊、蝇和其他昆虫的杀灭效果。结果大灭浸泡蚊帐后第27天,对蚊类还具有较好的杀灭效果;奋斗呐浸泡蚊帐后第21天的杀灭效果明显下降,帐顶死蚊数仅为浸泡蚊帐第9天的33%。比较大灭组与奋斗呐组第21天帐顶蚊(蚊:Z=2.373,P=0.015)和第24天帐顶蝇及其他昆虫死亡数(蝇:Z=1.783,P=0.047;其他昆虫:Z=2.096,P=0.026)差异均有统计学意义,前者死亡数明显较后者为多。结论2种杀虫剂浸泡蚊帐后均能达到防治有害昆虫的目的,但大灭的持效时间更长,效果更好些。     

Evaluation of a mass distribution programme for fine-mesh impregnated bednets against visceral leishmaniasis in eastern Sudan

During an epidemic of visceral leishmaniasis (VL) in eastern Sudan, Médecins Sans Frontières distributed 357,000 insecticide-treated bednets (ITN) to 155 affected villages between May 1999 and March 2001. To estimate the protective effect of the ITN, we evaluated coverage and use of ITN, and analysed VL incidence by village from March 1996 to June 2002. We provided ITN to 94% of the individuals >5 years old. Two years later, 44% (95% CI 39-48%) of nets were reasonably intact. Because ITN were mainly used as protection against nuisance mosquitoes, bednet use during the VL transmission season ranged from <10% during the hot dry months to 55% during the beginning of the rainy season. ITN were put up from 9 to 11 p.m., leaving children unprotected during a significant period of sandfly-biting hours after sunset. Regression analysis of incidence data from 114 villages demonstrated a significant reduction of VL by village and month following ITN provision. The greatest effect was 17-20 months post-intervention, with VL cases reduced by 59% (95% CI: 25-78%). An estimated 1060 VL cases were prevented between June 1999 and January 2001, a mean protective effect of 27%. Although results need to be interpreted with caution, this analysis indicates a potentially strong reduction in VL incidence following a community distribution of ITN. The effectiveness of ITN depends on behavioural factors, which differ between communities.     

Control of pyrethroid-resistant Anopheles gambiae and Culex quinquefasciatus mosquitoes with chlorfenapyr in Benin

Objective  To compare the efficacy of chlorfenapyr applied on mosquito nets and as an indoor residual spray against populations of Anopheles gambiae and Culex quinquefasciatus in an area of Benin that shows problematic levels of pyrethroid resistance.
Method  Eight-week trial conducted in experimental huts.
Results  Indoor residual spraying killed 82.9% of An. gambiae overall (mean mortality: 79.5%) compared to 53.5% overall (mean mortality: 61.7%) in the hut containing the lower dosed ITN. Analysis of data on a fortnightly basis showed high levels of mosquito mortality and blood-feeding inhibition during the first few weeks after treatment. Control of C. quinquefasciatus by the IRS and ITN interventions showed a similar trend to that of An. gambiae and though the average level of mortality was lower it was still much higher than with pyrethroid treatments against this population. Chlorfenapyr's reputation for being rather slow acting was evident particularly at lower dosages. The treatments showed no evidence of excito-repellent activity in this trial.
Conclusion  Chlorfenapyr has the potential to control pyrethroid resistant populations of A. gambiae . There is a need to develop long-lasting formulations of chlorfenapyr to prolong its residual life on nets and sprayed surfaces. On nets it could be combined with a contact irritant pyrethroid to give improved protection against mosquito biting while killing pyrethroid-resistant mosquitoes that come into contact with the net.     

A comparison of use of a pyrethroid either for house spraying or for bednet treatment against malaria vectors

In an intensely malarious area in north-east Tanzania, microencapsulated lambdacyhalothrin was used in four villages for treatment of bednets (provided free of charge) and in another four villages the same insecticide was used for house spraying. Another four villages received neither intervention until the end of the trial but were monitored as controls. Bioassays showed prolonged persistence of the insecticidal residues. Light traps and ELISA testing showed reduction of the malaria vector populations and the sporozoite rates, leading to a reduction of about 90% in the entomological inoculation rate as a result of each treatment. Collections of blood fed mosquitoes showed no diversion from biting humans to biting animals. Incidence of re-infection was measured by weekly monitoring of cohorts of 60 children per village, after clearing pre-existing infection with chlorproguanil-dapsone. The vector control was associated with a reduction in probability of re-infection per child per week by 54–62%, with no significant difference between the two vector control methods. Cross-sectional surveys for fever, parasitaemia, haemoglobin and weight showed association of high parasitaemia with fever and anaemia and beneficial effects of each intervention in reducing anaemia. However, passive surveillance by resident health assistants showed no evidence for reduced prevalence of fever or parasitaemia. Net treatment consumed only about one sixth as much insecticide as house spraying and it was concluded that the former intervention would work out cheaper and nets were actively demanded by the villagers, whereas spraying was only passively assented to.