Towards better diagnosis / by David Payne

DiHerent strategies for diHerent situations human settlements in rural areas, for example, settlements related to development projects, present simi- lar characteristics. The physical planning for all such areas should include selection of a suitable site and the provision of environmental sanitation to eliminate existing breeding sites and prevent the cre- ation of new, artificial, ones. In addition, man-mosquito contact can be reduced by improved house con- struction and protection. • Coastal and marshland malaria is related to the presence of mosquitos which breed specifically in brackish water. In South-East Asia and the Pacific Islands, these can be respon- sible for very serious problems. In some places, the development of tourism entails control requirements and options similar to those of urban planning. Some areas are amenable to engineering measures such as drainage, filling and flushing of estuaries or c-anals with sea water. • Malaria in war zones and areas with sociopolitical disturbances. These events result in the displacement of populations, breakdown of health care and disruption of agriculture that may increase mosquito breeding. Serious outbreaks may result. Depending on the situation and the resources available, it may be possible to consider mass fever treatment, temporary prophylaxis, spraying of shelters as well as per- sonal protection. Smallpox was eradicated because of a "magic bullet" - a very effective vaccine was available. The fight against malaria is more complicated because the potential for transmission and the effectiveness of control measures varies with the different characteristics of the plasmodium, climate and physi- cal environment, and the habits of the people vary from place to place. But we do have the technical means to dramatically reduce the impact of malaria. What is needed is political will, a minimum of well-managed resources, dedicated malaria specialists and general health workers, and - maybe above all - active participation by people everywhere. · • 12 Dr Peter /. Trigg is a Scientist with the Malaria Control Unit. WHO. 1211 Geneva 27 , Switzerland Towards_ better diagnosis by David Payne I n 1880 a French army doctor, A. Laveran, working in Algeria, took some blood from a sick soldier. Examining it under his primitive micro- scope, he saw, and subsequently described, what we know today to be the parasites of Plasmodium fa/ciparum. One hundred and ten years later we still use the combination of the human eye and the ordinary microscope to make the definitive diagnosis of malaria. Of course, since Laveran's time, there have been great improve- ments in the optical quality of the microscopes, and special stains have been developed which colour the parasites so that they can be more easily recognized. Today an experi- enced microscopist working at a mag- nification of 600 to 700 times can readily detect and identify all four species of human malaria parasite and, by determining which blood forms of the parasite are present and in what numbers, can greatly assist the doctor in choosing the appropriate treatment for that patient. In addition, by follow- ing up the patient with further blood examinations, the microscopist can aid the doctor in monitoring the patient's progress by quickly detecting any signs of treatment failure. Unfortunately, such a level of micro- scopy requires resources of materials and skills which · are not always available-particularly at the village level of the health services of the most malarious countries, where the major- ity of the malaria infections are treated. Malaria research workers have always been in the vanguard of the efforts to find new and better diag- nostic methods to facilitate the rapid diagnosis of malaria at the remotest points of the health care system. An early approach was to detect the antibodies that a person suffering from malaria produces against the parasite. But this procedure is time-consuming, and high levels of antibody may only be present after the infection has been active for some time: too late for the rapid and early diagnosis which is essential for effective treatment, parti- cularly when the patient is seriously ill. Nevertheless, these techniques have proved to be of great value to medical specialists studying the long-term effects of the disease in the com- munity. Another approach has been to identify particular groups of molecules which occur on, and are specific to, a particular species of the malaria para- site. These antigens, so called because they stimulate and react with the antibodies of the malaria patient, can be readily detected and identified. But the techniques needed are rather complex and time-consuming, and are not yet of the same reliability as good microscopic diagnosis. The article by Professor Lebras on page 29 explains how new techniques will in the future greatly facilitate diagnosis. Current experiments aimed at enhancing the power of detection of these techniques will replicate the selected parts of the genes millions, or even billions, of times to allow their detection by simple visual methods which are rapid, cheap and reliable. Photo WHO/P. Plttet lt is hoped that these new tech- niques will lead to the mass production of simple diagnostic tools based on a dipstick or card. A small quantity of blood obtained from a finger prick will be brought into contact with the surface of the dipstick or card, where, if malaria parasites are present, incorpo- rated reagents will react with specific molecules in the malaria parasites to produce a visible reaction . In this way it should be possible to identify what parasite forms are there, and give a good estimate of the density of the infection. A similar test system could also tell the doctor which antimalarial drug, if any, the malaria patient had already taken and how much; and to what degree the parasite is resistant to the common antimalarial drugs. Armed with this information, the treatment of malaria patients at all levels of the health service would be enhanced, and the battle for the con- trol of the disease would be made that much easier and more effective. • ~~-------------------------,1 , Dr David Payne is a Scientist with the Malaria Control Unit and the Special Programme for Research and Training in Tropi- cal Diseases. WHO. 1211 Gen- eva 27 . Switzerland. W ORLD HEALTH . September-October 1991