The challenges of doing more against malaria, particularly in Africa.

The malaria theme section of this issue ofthe Bulletin covers a wide range of topics,from combination therapy (pp. 1378–1388)and insecticide-impregnated mosquito nets(pp. 1389–1400) to the possible use ofgenetically modified Anopheles for vectorreplacement (pp. 1412–1423), from the useof geographical information systems inthe planning, execution and monitoringof interventions (1401–1411; 1438–1444)to the potential role of post-genomics inthe development of new antimalarial drugs(1424–1437). Interestingly, previous issues of theBulletin dedicated to the same subject(e.g. Vol.11, No. 4–5, 1954) were compara-tively uniform in content, reflecting theWHO emphasis of the time on malariaeradication by indoor spraying. The widercurrent view reflects the maturing of malar-iology as a multidisciplinary science withinput from genetics and molecular biologyand other cutting-edge disciplines. It alsoreflectstheflexibilityoftheRollBackMalaria(RBM) policy, which advocates an openstrategy of critical evaluation and malariacontrol programmes geared to diverse andchanging local situations.The emphasis of this issue of theBulletin (and of this editorial) is on control-ling malaria mortality, for which Africabears the bulk of the world’s burden. Theevolving biodiversity of the continentincludes man, his most pathogenic malariaparasite, Plasmodium falciparum, and its mostanthropophilic mosquito vector, Anophelesgambiae. The breeding of this mosquito isfavoured by man-made ecological changesrangingfromNeolithicagriculturetocurrentpractices of deforestation and irrigation.The outcome is an exceptionally closehuman–vector association which producesmean parasite inoculation rates exceeding100 infective bites per year per person inmost rural villages of sub-Saharan Africa,whereas less than one infective bite perperson is recorded in most residual endemicareasofSouth-EastAsiaandSouthAmerica.The eradication of this extremely stableAfrican population of P. falciparum isunattainable in the absence of new tools.This being so, the strengthening of diseasecontrol is the only realistic short-termstrategy. Despite increasing drug resistance,malaria is still a curable disease, and thecommitment to fight it, clearly expressedby African political leaders in the recentAbuja summit, should make it possible tomobilize financial and human resourcesfor drug supply and distribution all the wayto the smallest and poorest malaria-endemicrural communities. Guidance for thismultisectoral effort is provided by specificoperational research such as analysis ofthe logistic, cultural and economic causesfor delayed treatment, which is still a majorfactor of malaria mortality. Research shouldalso be done to make accurate estimatesoftheburdenofdiseaseimposedbymalaria,and to determine the impact of hostand parasite genotypes (1) and associatedpathologies (2) on malaria disease severity.On the other hand, combating thedisease must be distinguished from combat-ingtheinfectionandthislatteractivityshouldbeseenwithinalong-termstrategyaimingatthe interruption of trasmission even whereP. falciparum reaches its highest stability. Inthese holoendemic and hyperendemic areas,particularly in West African Guinea andthe Sudan savanna belts, indoor residualspraying or impregnated mosquito nets arenotenough.Ifsuccessfullyapplied,theymaybring about a temporary reduction in vectorcapacity but they will not lower it belowits critical level. Thus, the possibilityof achieving a cost-effective, sustainableequilibrium that is more favourable to thehumanhostisamatterforcarefulevaluation.It must take fully into account the risk thatreduced inoculation rates may result inunstablemalariaconditionsthatmayworsenthe clinical picture and outcome of thedisease. Vector control measures, whichare the rule in tropical Asia and SouthAmerica, are limited in Africa to areasselected according to epidemiological data,historical records and available resources.The focus should be on hypoendemic,or epidemic-prone zones of the continent(such as high altitude areas), where localvector populations of An. gambiae andAn. funestus are so dependent on indoorresting that indoor spraying of residualinsecticides has proved crucial for theirreduction or even eradication.Research on new antimalarials couldconcentrate on vaccines and new drugs.A multi-stage vaccine plus a monodoseantimalarial treatment with gametocytocidaleffect in addition to the already availableimpregnated mosquito nets could turnthe dreamoferadicatingP. falciparum malariain sub-Saharan Africa into a reality. Furtheranti-vector measures could be integrated,among which a full-night-lasting repellentwould certainly be worth while. But, sincethe integration of these tools could provedifficult or insufficient, a more diversifiedresearch programme might be needed.Research on biting and oviposition beha-viour in view of trapping systems, aswell as genetic manipulation of the vectorin view of replacement programmes, couldlead the way to highly innovative andeffective vector control tools.Finally, it must never be forgottenthat social and economic instabilityhas helped to perpetuate the burdenof malaria. Where conditions are stable,the prospects for disease control aregreatly improved. n