What is malaria

Malaria a global crisis

• Malaria is a public health problem today in more than 90 countries, inhabited by a total of some 2400 million people, 40% of the world's health population.
• Worldwide prevalence of the disease is estimated to be in order of 300-500 million cases per year.
• More than 90% of all cases are in sub-Saharan Africa.
• Mortality due to malaria is estimated to be over 1 million deaths each year. The vast majority of deaths occur among young children in Africa, especially in remote rural areas with poor access to health services.
• Other high risk groups are pregnant women, and non-immune travellers, refugees or laborers all entering endemic areas.
   

Malaria and the problems of control

Malaria still remains among the most devastating diseases occurring in the world today. It is estimated that around 100 million clinical cases may occur every year in tropical Africa alone, where changes in the epidemiological situation in the last few years have resulted in an increased frequency of the disease. While malaria remains under control in most developed and stable areas, the situation is deteriorating in all frontier areas of economic development, i.e. in areas where the exploitation of natural resources or illegal trade occurs, in jungle areas or areas burdened with problems of civil war and other conflicts, and where mass movements of refugees exist. Increasing drug resistance, decreasing efficacy of vector control efforts and weak health infrastructure may also affect the control of this disease. In addition, the expected rise in global temperature might herald an increase in the geographical distribution of malaria transmission, perhaps impinging upon Europe and the United States.

Travellers and malaria

The worsening malaria problem has increased the risk of acquiring malaria for visitors to endemic areas. Imported malaria in tourists, business travellers and immigrants is an increasing problem in Europe and the United States. Dutch travelers can visit the site of the Landelijk Coördinatie Centrum Reizigersadvisering listed on our links page, for more information about prevention (prophylaxis) of human malaria.

The parasite and the disease

Malaria is an infectious disease transmitted by Anopheline mosquitoes. It is caused by parasitic protozoa of the genus Plasmodium, and alternates between human and mosquito hosts. Four species of Plasmodium infect men, of which three (P. vivax, P.ovale, P. malariae) may cause serious illness, but are rarely fatal. The fourth, P. falciparum, is the most highly pathogenic and causes much more severe and progressive illness in non-immune persons, often leading to coma and death within a few days. In endemic areas the heaviest toll of morbidity and mortality falls on young children but malaria is a relatively mild condition in adults. This is due to (a slow) acquisition of specific immunity, although complete immunity to infection is never achieved. Symptoms of malaria include fever, shivering, pain in the joints, headache, repeated vomiting, generalized convulsions and coma. Severe anaemia is often the attributable cause of death in areas with intense malaria transmission.

Problems of prevention and cure

Prevention of malaria encompasses a variety of measures that may protect against infection or against the development of disease in infected individuals. Measures that protect against infections are directed against the mosquito vector. These can be personal (individual or household) protection measures e.g. protective clothing, repellents, bednets, or community/population protection measures e.g., use of insecticides or environmental management to control transmission. Measures which protect against disease but not against infection include chemoprophylaxis.

Drugs and drug resistance

^{Spread of chloroquine resistance of P. falciparum}

A small number of drugs are available for the cure of a malaria infection. One of the most alarming problems in the treatment and control of malaria is the spread of resistance to anti-malarial drugs in most tropical areas. In South-East Asia, for example, strains of P. falciparum may be resistant to most or all conventional drugs. Although some new drugs have appeared in the last twenty years, new (especially inexpensive and affordable) drugs and more practical formulations of existing drugs are badly needed. In spite of drug resistance , malaria is a curable disease, not an inevitable burden. Although there is only a limited number of drugs, if these are used properly and targeted to those at greatest risk, malaria disease and deaths can be reduced, as has been shown in many countries. For information on the available drugs against malaria visit the website of the WHO, listed on our links page.

Vaccines

An effective vaccine would constitute a powerful addition to malaria control. Progress in the development of an effective vaccine is slow. This is despite intensive research efforts on elucidation of protective immune responses, identification of antigenic targets and development of vaccine delivery systems. Vaccines, produced by recombinant technology or peptide synthesis, showed so far a disappointing and low efficacy in protecting against clinical malaria. Different parasite-specific features and characteristics of the interaction of human immune system and the parasites, might explain the difficulties in developing effective immuno-therapeutic intervention strategies.

^{Disruption of the malaria life cycle by different types of vaccination}

The three main types of vaccine being developed are:

• 'Anti-sporozoite' or 'pre-erythrocytic' vaccines, designed to prevent infection.
• 'Anti-asexual blood stage' vaccines, designed to reduce severe and complicated manifestations of the disease.
• 'Transmission-blocking' vaccines, designed to arrest the development of the parasite in the mosquito, thereby reducing or eliminating transmission of the disease

Future

There are no simple solutions to the world's malaria problem and it is unlikely that a single strategy for control will be applicable to all countries and all epidemiological situations. To be assured of a package of effective intervention strategies for the future, a rational approach to the problem of malaria is required in combination with intensive research efforts on different approaches to control malaria. Expansion of our understanding of the biology, epidemiology, pathogenesis and clinical manifestations of this complex, heterogeneous disease will be critical to the development of additional strategies for control. In 1998 an initiative of WHO, UNDP, UNICEF and Worldbank was announced to reduce the malaria burden: Roll Back Malaria. The RBM partnership includes governments, development agencies, conmmercial organisations, civil society, research groups and the media.

The life cycle of malaria parasites

1. An infected female Anopheles mosquito bites, injecting Plasmodium parasites into the blood. They pass quickly into the liver.
2. The parasites multiplies in liver cells over the next 7-10 days, causing no symptoms.
3. Parasites burst from the liver cells to invade more erythrocytes and multiply again. The parasites invade more erythrocytes. This cycle is repeated, causing fever each time parasites break free and invade.
4. If a female Anopheles-mosquito feeds on this patient, parasites will muliply in her stomach wall. Thousands of new parasites migrate to her salivary glands, to be injected in saliva when next she feeds.
5. The mosquito inoculates another human.

 

Downloads

• Malaria informatie RIVM (PDF, 390.3 KB)
• Malaria in de wereld (MOV, 2.5 MB)