Malaria and you / by Louis Molineaux and José A. Najera

Malaria and vou by Louis Molineaux and Jose A. Najera Malaria is arguably the most important health risk run by travellers, and the problem is getting larger and more complicated thanks to the increase in travel, the deterioration of the malaria situation in many areas, and the increase in drug resistance. The days are gone when a single very safe drug, chloroquine , afford- ed almost total protection against all species of malaria everywhere . The new, more complex, situation requires travellers to take increas- ing responsibility for their own pro- tection against malaria and its con- sequences , and therefore to seek the relevant information. There are about 100 million new cases of malaria every year, and it causes several hundred thousand deaths each year. Malaria eradica- tion has succeeded in some- mainly temperate and relatively devel- aped-countries, but has failed in many others, mainly tropical and relatively less developed. In many areas the situation is deteriorating, for a variety of reasons, including resistance of the vectors to insecti- cides and of the parasites, especially the malignant parasite Plasmodium falciparum, to antima- larial drugs. The countries affected are, in cooperation with WHO, adapting their malaria control strat- egies to the changing situation. Malaria is transmitted from per- son to person by mosquitos of the genus Anopheles, biting between sunset and sunrise. For an infected mosquito to become infective re- quires a warm ambient temperature and a period of one to two weeks. The traveller's first line of defence is to protect himself or herself from mosquito bites. (See article on Biting insects.) The abundance of infective mos- quitos varies enormously between the malarious countries of the world, and also within the same malarious country. The worst af- fected areas are rarely visited by tourists; thus within Thailand, the malaria risk is negligible in Bang- kok, high near the Kampuchean border; within Kenya, the risk is negligible in Nairobi , high in the coastal area; within China, the risk is negligible in all areas commonly visited by tourists, high near the Burmese and Vietnamese borders. There are different species of malaria parasites, one malignant (Plasmodium falciparum), the oth- ers (mainly Plasmodium vivax) rel- atively benign. In certain malarious areas , the infected mosquitos in- oculate the benign parasites either exclusively (e.g. the malarious areas of Peru, Paraguay, Afghani- Epidemiological assessment of the status of malaria, 1985 8 Indicating areas that are free from malaria, those where there is a slight risk, and those where the disease poses a threat to unprotected travellers Q Areas in which malaria has disappeared, @) Areas with limited risk @) Areas where malaria transmission occurs I I ©World Health Organi zation 1987 WoRLD HEALTH, December 1987 stan and Turkey) or predominantly (e.g. most of the malarious areas of China, India and Pakistan). In Africa south of the Sahara , how- ever, the malignant parasites predominate . The malignant parasites incubate for nine to 30 days in the liver before emerging in the blood and causing disease ; the benign para- sites may incubate longer. There- fore a disease starting less than nine days after first exposure is most probably not malaria; a disease starting more than 30 days after last exposure is most probably not ma- lignant malaria , but may be benign malaria. It follows too that , if a short-term traveller is infected with malaria , the disease will often man- ifest itself only after return to the home country (where the doctor may fail to think about it , and the laboratory may lack expertise !) All of the drugs recommended for prophylaxis act on the parasites after their emergence from the liver ; hence the need to continue prophylaxis for 30 days after the last exposure. In addition , one of those drugs (proguanil) also acts on the malignant species of malaria parasites in the liver. W ORLD HEALTH, December 1987 Plasmodium falciparum is be- coming increasingly resistant to an increasing number of drugs in an in- creasing number of countries , so recommendations about drug regi- mens, either prophylactic or thera- peutic, require regular updating. Even if the most up-to-date recom- mendations are obtained and fol- lowed, no prophylactic regimen is 100 per cent protective ; hence the diagnosis of malaria should not be dismissed because the patient was on drug prophylaxis. Equally, even Cysts of a malarial parasite developing on the wall of a mosquito 's stomach. Scanning electro-micrograph by M.D. Smith if a prophylactic regimen fails to protect against the occurrence of infection and disease, it may never- theless succeed in rendering the disease milder and less threaten- ing to life. The typical manifestations of ma- laria are bouts of high fever lasting a few hours , starting dramatically with shaking chills , subsiding dra- matically with profuse sweating, and reappearing at regular inter- vals , most commonly every 48 hours . But symptoms are often atypical in the first few days and are less typical in malignant than in be- nign malaria ; so malaria should be thought of in all otherwise unex- plained cases of fever in travellers who may have been exposed. Malignant malaria kills many people even though it is relatively easy to diagnose and cure. The most important survival factors are early diagnosis and treatment. A traveller who may have been ex- posed and who develops a fever at 9 Spraying against mosquito swarms in southern France. Photo WHO/P. Almasy the appropriate time should be aware that it might be malaria and should seek prompt medical atten- tion. It is vital to remind the doctor that it might be malaria, of which most doctors in non-malarious countries have little experience. In certain situations, prompt medical attention may not be avail- able. So the traveller may be ad- vised to carry certain specified anti- malarial drugs for emergency self- treatment, and should still seek medical attention at the earliest opportunity. No drug is totally devoid of un- pleasant side-effects in all people , and some drugs cause serious, even life-threatening, adverse reactions in a few people. Certain drugs may be contra- indicated for certain groups of 10 Three things travellers can do about malaria 1. Inquire beforehand about the ma- laria risk and appropriate measures for the specific areas they consider visiting. Sources of information: their physician; specialised national and international institutions; WHO's "Vaccination Certificate Require- ments and Health Advice for Interna- tional Travel" published every Near in English, French, Spanish, German. Some countries, such as Thailand, offer the arriving traveller pertinent printed information, to which it is wise to pay careful attention. 2. Protect themselves as much as possible against mosquito-bites. 3. Be aware that they may have been exposed to malaria, that no chemoprophylactic regimen gives total protection to everybody, that malaria may occur several months, even (exceptionally) years, after ex- posure, and that the symptoms of . mqlaria may not be easy to reco- gnise; seek medical attention in case of fever and remember to men- tion to the physician the possibility of exposure to malaria. Malaria and you individuals. Sulfadoxine-pyrimetha- mine and sulfalene-pyrimethamine should not be given to persons with a history of allergy to any sulfona- mide. Infants and pregnant women should not be given these drugs , nor mefioquine , without medical super- vision; but they can, at the recom- mended doses, safely be given chlo- roquine, proguanil and quinine. Research on the development of new antimalarial drugs and of ma- laria vaccines is actively being pur- sued by many scientists, and some of the expected products will be useful for the protection of travel- lers . Another kind of research that is useful for improving and updat- ing the advice given to travellers consists of surveys addressed to the travellers themselves, inquiring about their travel, health and protective measures used. By cooperating with such surveys, today's travellers can help tomor- row's travellers-which may include themselves ! • W oRLD HEALTH, December 1987