Agame of chess by Michel Lebras

t a time when the East Asia, over 50% of the falciparum smallest vessels. Promising tests parasite's malaria found are already resistant to have been made with the antibodies of resistance to chloro­ mefloquine even though this drug has immunized people, and with chloro­ quine is spreading only been in use since 1984. quine, which could play a role in throughout Africa, all So it is vital to discover new inhibiting the harmful effects of toxic the way from the southern Sahara to medicaments. Research workers, substances. South Africa, while resistance to qui­ exploring various avenues, are thinking A great number of molecular nine and many other drugs-whether up new ways to attack the haemato­ substances are at present being exper­ taken singly or together-is advancing zoa; their affinity for certain lipids (fats), imented with, either in the laboratory in certain parts of Asia, tropical Amer­ for example, seems to offer a potential on cell cultures, in animals or in man. ica and East Africa, pharmacological strategy for creating new drugs. Natural substances extracted from the research has put at our disposal new The most serious forms of malaria traditional pharmacopoeia, such as the therapeutical weapons. These are could be controlled by using drugs qinghaosu mentioned above, are not mefloquine, halofantrine, and the which would prevent the infected red being overlooked in these tests. derivatives of a Chinese plant called blood cells from adhering to the wall of But at present a most promising qinghaosu-artesunate and the deep capillary vessels, the for­ approach is one which would enable artemether. mation of clusters of red cells in the us to overcome resistance to chloro­ Operational research is meanwhile form of "rosettes", and the release of quine by keeping the drug in contact helping us to plan the strategies for toxic substances, all of which result in with the parasite. Certain substances using these drugs. Studies are being such complications as bleeding and used in the treatment of cardiovascular made of their efficacy based on an the formation of blood clots in the diseases, such as antagonists of evaluation of the rates of cures achieved, of their harmlessness (by measuring the degree of tolerance in patients), of their cost (taking into account not only the price of the drug but also the cost of not treating malaria victims), and finally of their accessibility and the degree to which patients observe the prescribed regimens. "Does the large-scale use of the drugs have any overall impact on the malaria situation?" is another impor­ tant question. In fact, field trials have already shown that the correct use of these drugs has cut down mortality and considerably reduced morbidity from malaria.

A thinking parasite? The malaria parasites are haematozoa-that is, they live in human blood-and it is the small anopheles which transmits the parasites by biting, at random, first a malaria patient then a healthy per­ son. These parasites-and this is more true for falciparum than for any other-have a remarkable capacity for adapting themselves to drugs and thus escaping their effect. For instance, in certain foci in South-

The parasite has a remarkable capacity to develop resistance to drugs. Scientists are working hard to find new ones. The microscope slide shows the Plasmodium falciparum inside a red blood cell.

WORLD HEALTH . September-October 1991 A game of chess

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Catching to enable research making giant strides and gives us Deltamethrin in particular is desirable workers to learn more about the enemy. plenty of grounds for optimism. for its efficacy, its long-lasting action (as long as six months) and its harmless­ And a vaccine? ness for man and the environment. calcium or certain antidepressants and All research aimed at controlling The optimal ways of using these antihistamines, seem to be capable of malaria comes up against the complex substances depend on the biology of playing this role when they are admin­ nature of the parasite. It is possible to the mosquitos, and this ought, there­ istered with chloroquine. interrupt the development of the para­ fore, to form part of initial entomologi­ site at several points. The identification cal studies. Bednets, especially when Recognizing the parasite and choice of antigens which could they are impregnated with deltameth­ Diagnosing malaria at present form the basis for design of "candidate rin, have proved to be effective in depends on detecting the haematozoa vaccines" can be narrowed down by many evaluation studies. However, a in the blood by use of the microscope. analysing the natural history of malarial good deal of research still needs to be But this technique, in use for more immunity. Long-term research carried done before we can say exactly what is than a century, is of limited value when out in the little village of Dielmo in the role of impregnated bednets under there are only a few parasites in the Senegal has given us a better under­ various epidemiological conditions. blood. In fact, microscopy does not standing of how the mediators of There must be no letting up of enable us to distinguish between immunity operate. In an area where research. We have to find other weak human carriers of the disease who the transmission of malaria still con­ points in the haematozoa. We need to show no symptoms and active malaria, tinues, some children have several know more about how to use anti­ which calls for treatment. attacks of fever each month, while malarial drugs more effectively, to find New tests are at pr~ent under others never have them. The research better diagnostic techniques for the development. Thanks to the use of workers are trying to find out why. A different forms of malaria, and to molecular probes we can detect new technique now being developed improve the planning, programming, different fragments of the parasite in should make it possible to multiply management and evaluation of control the blood. some of the fragments of the parasite One particularly promising tech­ measures. which stimulate immunity. These The haematozoa is ingenious, nique, already being applied in the might be used to prepare an effective dauntless and apparently gifted with field, calls for the blood sample to be vaccine. eternal life. We are playing a game of separated by centrifuge in capillary chess with it. At stake are the lives of tubes and then coloured with acridine No contact with mosquitos, no malaria the 2000 children who succumb to orange. This makes it possible to malaria every day in the world. • detect the parasites, even when they If we could prevent all contact are few and far between. Today this between man and the anopheles mos­ method is the most sensitive and the quito which transmits malaria, this Professor Michel Lebras is quickest. However, its main drawback disease would not exist. The advent of Director of the Rene Labus­ is the lack of specificity, since it may synthetic pyrethroids which are cap­ quiere Institute at the Uni­ sometimes give a positive result even able of repelling the mosquitos, such versity of Bordeaux 11 , 146 when there is no malaria. Also, special as permethrin and deltamethrin, has rue Leo- Saignat, 33076 microscopes are needed. All the same, given us high hopes of considerably Bordeaux Cedex, France. molecular biology is undoubtedly reducing this insect-and-man contact.

30 WORLD HEALTH. September-October 1991