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House screening for malaria control

2009; Elsevier BV; Volume: 374; Issue: 9694 Linguagem: Inglês

10.1016/s0140-6736(09)61078-3

1474-547X

John E. Gimnig, Laurence Slutsker,

Travel-related health issues

After many years in the proverbial wilderness, vector control has again risen to prominence in malaria-control programmes. WHO now advocates universal coverage with longlasting insecticide-treated nets (LLINs), indoor residual spraying programmes are being reintroduced and expanded, and even larval control, long dismissed as inappropriate for sub-Saharan Africa, is being considered in selected areas. In The Lancet today, Matthew Kirby and colleagues1Kirby MJ Ameh D Bottomley C et al.Effect of two different house screening interventions on exposure to malaria vectors and on anaemia in children in The Gambia: a randomised controlled trial.Lancet. 2009; (published online Sept 3.)https://doi.org/10.1016/S0140-6736(09)60871-0Summary Full Text Full Text PDF Scopus (182) Google Scholar show the efficacy of another intervention aimed to reduce man–vector contact: screening of houses at the windows, doors, and eaves, or over the ceilings, lowered the numbers of mosquitoes entering houses and reduced anaemia in children from those houses. In this study, 500 houses were randomly assigned to receive full screening, ceiling screens, or no screens. The number of mosquitoes captured in traps in houses with full screening or screened ceilings was 59% and 47% lower, respectively, than the number trapped in houses with no screening. Children living in houses with full screening or screened ceilings were less likely to be moderately anaemic (haemoglobin <80 g/L) than were children living in houses with no screening. Although the benefits of house screening might seem obvious, its efficacy in preventing malaria has not previously been assessed in a prospective trial. There are many anecdotal reports suggesting that improved housing conditions contributed to the elimination of malaria in North America and Europe,2Boyd MF The influence of obstacles unconsciously erected against anophelines (housing and screening) upon the incidence of malaria.Am J Trop Med. 1926; 6: 157-160Google Scholar, 3Watson RB Maher HC An evaluation of mosquito-proofing for malaria control based on one year's observations.Am J Hyg. 1941; 34: 86-94Google Scholar but the effects of these modifications were not rigorously measured and were probably confounded by other contemporaneous vector-control methods. In today's evidence-based climate, such anecdotes are insufficient to convince policy makers. In the USA, larval control with Paris Green (a copper acetoarsenite), water management, and house spraying with DDT (dichlorodiphenyltrichloroethane) are often given most credit for the ultimate elimination of malaria. However, malaria was in steep decline well before the advent of these interventions,4Williams LL Malaria eradication in the United States.Am J Public Health. 1963; 53: 17-21Crossref Google Scholar and some experts have suggested that changes in social conditions, including improved housing, accounted for much of the decline of malaria in Europe and North America.5De Zulueta J Malaria and ecosystems: from prehistory to posteradication.Parassitologia. 1994; 36: 7-15PubMed Google Scholar This notion does not discount DDT and other interventions—they were clearly effective in uprooting malaria from southeastern USA where it was most firmly entrenched—but emphasises that the contribution of house screening to malaria control was probably not trivial. Despite Kirby and colleagues' positive results, there are several barriers to overcome before house screening is given the same priority as interventions such as LLINs or indoor residual spraying for malaria-control programmes. First, evidence from a range of ecoepidemiological settings will be needed to convince policy makers that this intervention is broadly applicable throughout other malarious areas in sub-Saharan Africa. Second, Kirby rightly points out that house screening would be an ideal instrument for integrated vector-management. However, today's study was done in a setting with low coverage of insecticide-treated nets. Thus the study could not address whether the effect of house screening would be additive or even synergistic with that of LLINs. Resources for malaria prevention are limited. With an already stated global commitment to LLINs, robust evidence of equivalence or superiority would be needed before resources are diverted from scale-up of LLINs to house screening. There are also several technical questions related to house screening that will need to be addressed. For example, how long does the screening material last? If a few holes develop, does the efficacy decline and, if so, should screening material be treated with insecticide? In view of the fairly high cost of screening, some additional evidence that this intervention will last for several years would be needed to convince policy makers that house screening is a worthwhile investment. Perhaps the greatest barrier to widescale implementation of house screening will be the question of who pays for it. Kirby and colleagues report that house screening in The Gambia costs about US$10 per person if netting is donated free of charge, making it much more expensive than either LLINs or indoor residual spraying6Yukich JO Lengeler C Tediosi F et al.Costs and consequences of large-scale vector control for malaria.Malar J. 2008; 7: 258Crossref PubMed Scopus (109) Google Scholar unless the cost is averaged over the expected life of the screening material, an approach few donors seem to take. The sometimes contentious debates between those advocating free nets and those advocating market-based approaches7Curtis C Maxwell C Lemnge M et al.Scaling-up coverage with insecticide-treated nets against malaria in Africa: who should pay?.Lancet Infect Dis. 2003; 3: 304-307Summary Full Text Full Text PDF PubMed Scopus (113) Google Scholar, 8Lines J Lengeler C Cham K et al.Scaling-up and sustaining insecticide-treated net coverage.Lancet Infect Dis. 2003; 3: 467-468Summary Full Text Full Text PDF PubMed Scopus (47) Google Scholar are likely to resurface should house screening be strongly advocated for malaria prevention. Such a debate would be further complicated by the fact that those with the largest houses and thus needing the most resources are probably those who would be most able to afford the installation of screening material. However, perhaps indoor residual spraying is a more appropriate analogy. Itself a rather costly intervention, no one thinks about charging homeowners on the basis of the square footage of their house. Despite the challenges to implementing house screening, Kirby and colleagues provide evidence that this intervention is effective in reducing exposure to malaria-vector mosquitoes and anaemia in children. LLINs and indoor residual spraying have their own challenges but are being successfully implemented in sub-Saharan Africa. Improved housing might have a role in African settings too: several recent studies have shown that changes in housing design reduce the number of anopheline mosquitoes entering houses,9Atieli HE Menya D Githeko A Scott T House design modifications reduce indoor resting malaria vector densities in rice irrigation scheme area in western Kenya.Malar J. 2009; 8: 108Crossref PubMed Scopus (75) Google Scholar, 10Lindsay SW Jawara M Paine K Pinder M Walraven GE Emerson PM Changes in house design reduce exposure to malaria mosquitoes.Trop Med Int Health. 2003; 8: 512-517Crossref PubMed Scopus (158) Google Scholar and anecdotal evidence suggests that improved housing might be associated with a decrease in malaria prevalence in Dar es Salaam, Tanzania.11Geissbühler Y Kannady K Chaki PP et al.Microbial larvicide application by a large-scale, community-based program reduces malaria infection prevalence in urban Dar es Salaam, Tanzania.PLoS ONE. 2009; 4: e5107Crossref PubMed Scopus (158) Google Scholar We hope that today's report will spur further interest in the assessment of the potential of house screening to help reduce and eventually eliminate malaria. We declare that we have no conflicts of interest. Effect of two different house screening interventions on exposure to malaria vectors and on anaemia in children in The Gambia: a randomised controlled trialHouse screening substantially reduced the number of mosquitoes inside houses and could contribute to prevention of anaemia in children. Full-Text PDF Open Access