Malaria is a common, serious and sometimes fatal tropical disease. It is a protozoal infection transmitted to human beings by mosquitoes biting mainly between sunset and sunrise. Human malaria is caused by four species of Plasmodium protozoa: Plasmodium falciparum, P.vivax, P. ovale and P.malariae. Malaria is a public health problem in over 100 countries worldwide, inhabited by some 40% of the world population, i.e. over 2 billion people.
Yes. It has been estimated that the incidence of malaria in the world may be in the order of 300 to 500 million clinical cases each year. Countries in tropical Africa account for more than 90% of these. Malaria mortality is estimated at almost 3 million deaths worldwide per year. The vast number of malaria deaths occur among young children in Africa, especially in remote rural areas with poor access to health services. Other high risk groups include women during pregnancy, and non-immune travelers, refugees, displaced persons, or labor forces entering into endemic areas.
Yes. Malaria is a leading cause of death and disease worldwide, especially in developing countries. Most deaths occur in young children. For example, in Africa, a child dies from malaria every 30 seconds. Because malaria causes so much illness and death, the disease is a great drain on many national economies. Since many countries with malaria are already among the poorer nations, the disease maintains a vicious cycle of disease and poverty.
No, not in all parts of the world. Malaria has been eradicated from many developed countries with temperate climates. However, the disease remains a major health problem in many developing countries, in tropical and subtropical parts of the world.
An eradication campaign was started in the 1950s, but it failed globally because of problems including the resistance of mosquitoes to insecticides used to kill them, the resistance of malaria parasites to drugs used to treat them, and administrative issues. In addition, the eradication campaign never involved most of Africa, where malaria is the most common.
Malaria typically is found in warmer regions of the world -- in tropical and subtropical countries. Higher temperatures allow the Anopheles mosquito to thrive. Malaria parasites, which grow and develop inside the mosquito, need warmth to complete their growth before they are mature enough to be transmitted to humans.
Malaria occurs in over 100 countries and territories. More than 40% of the world's population is at risk. Large areas of Central and South America, Hispaniola (the Caribbean island that is divided between Haiti and the Dominican Republic), Africa, the Indian subcontinent, Southeast Asia, the Middle East, and Oceania are considered malaria-risk areas.
Yet malaria does not occur in all warm climates. For example, economic development and public health efforts have eliminated malaria from the southern United States, southern Europe, Taiwan, Singapore, and all of the Caribbean islands (except Hispaniola). Some Pacific islands have no malaria because Anopheles mosquitoes are not found there.
In Africa south of the Sahara, the principal malaria mosquito, Anopheles gambiae, transmits malaria very efficiently. The type of malaria parasite most often found, Plasmodium falciparum, causes severe, potentially fatal disease. Lack of resources and political instability can prevent the building of solid malaria control programs. In addition, malaria parasites are increasingly resistant to antimalarial drugs, presenting one more barrier to malaria control in that continent.
Usually, people get malaria by being bitten by an infected female Anopheles mosquito. Only Anopheles mosquitoes can transmit malaria and they must have been infected through a previous blood meal taken on an infected person.
When a mosquito bites, a small amount of blood is taken in which contains the microscopic malaria parasites. The parasite grows and matures in the mosquito's gut for a week or more, then travels to the mosquito's salivary glands. When the mosquito next takes a blood meal, these parasites mix with the saliva and are injected into the bite.
Once in the blood, the parasites travel to the liver and enter liver cells to grow and multiply. During this "incubation period", the infected person has no symptoms. After as few as 8 days or as long as several months, the parasites leave the liver cells and enter red blood cells. Once in the cells, they continue to grow and multiply. After they mature, the infected red blood cells rupture, freeing the parasites to attack and enter other red blood cells. Toxins released when the red cells burst are what cause the typical fever, chills, and flu-like malaria symptoms.
If a mosquito bites this infected person and ingests certain types of malaria parasites ("gametocytes"), the cycle of transmission continues.
Because the malaria parasite is found in red blood cells, malaria can also be transmitted through blood transfusion, organ transplant, or the shared use of needles or syringes contaminated with blood. Malaria may also be transmitted from a mother to her fetus before or during delivery ("congenital" malaria).
Malaria is not transmitted from person to person like a cold or the flu. You cannot get malaria from casual contact with malaria-infected people.
Anyone can get malaria. Most cases occur in residents of countries with malaria transmission and travelers to those countries. In non-endemic countries, cases can occur in non-travelers as congenital malaria, introduced malaria, or transfusion malaria.
Plasmodium falciparum causes severe and life-threatening malaria; this parasite is very common in many countries in Africa south of the Sahara. People who are heavily exposed to the bites of mosquitoes infected with P. falciparum are most at risk of dying from malaria. People who have little or no immunity to malaria, such as young children and pregnant women; or travelers coming from areas with no malaria, are more likely to become severely ill and die. Poor people living in rural areas who lack knowledge, money, or access to health care are more vulnerable to the disease. As a result of all these factors, an estimated 90% of deaths due to malaria occur in Africa south of the Sahara; most of these deaths occur in children under 5 years of age.
Malaria epidemics, if uncontrolled, follow a natural course: The epidemic grows in a series of steps representative of the incubation interval (the period between the occurrence of infective gametocytes in the primary case and their reappearance in a secondary case), which is about 20 days for P.vivax and 35 days for P.falciparum. The length of the incubation interval and the degree of the reproduction rate determine the rate of multiplication of transmission, which is much faster in P.vivax epidemics than in those due to P.falciparum. In areas where both P.vivax and P.falciparum are present, the initial stages of an epidemic will thus be determined by a predominance of P.vivax infections and a very gradual increase in severity of the epidemic, while in later stages P.falciparum is likely to be abundant.
The peak of new infections due to a P.falciparum epidemic will only be reached when roughly 50 percent of the population at risk is infected, unless climatic changes (notably colder temperatures) prevent further transmission.
Control of a malaria epidemic involves relieving the immediate clinical consequences, preventing the progress of the epidemic (in time and space), and preventing future recurrences of the epidemic. This means improving disease management and providing some form of transmission control.
Epidemics occur when non-immune and partially-immune populations are exposed to high rates of inoculation. Potential epidemic situations can to a large extent be identified by combining some basic knowledge of the malaria situation in an area with general aspects of the geography, history and socio-economic situation. Potential epidemic situations include: areas of unstable malaria where conditions for malaria transmission are marginal in terms of altitude, rainfall patterns or temperature areas where the level of endemic malaria has been reduced and the malaria situation has become unstable after mass drug administration and/or vector control programs, which can no longer be sustained situations where non-immunes migrate into an endemic area. This would include refugee movements, and migration of labor forces into endemic areas situations where persons harboring malaria parasites migrate into a non-endemic, but receptive area. Receptivity refers to an abundant presence of anopheline vectors and/or the existence of other ecological and climatic factors favoring malaria transmission.
The size and impact of potential epidemics can only to a lesser extent be foreseen. Insufficient coverage of the population by health care services will exacerbate the impact.
In situations where a potential for malaria epidemics has been identified, responsible health services should be prepared to counter a beginning epidemic rapidly. Updated contingency plans should be at hand. At present many epidemic prone situations will, by their nature, stretch across national boundaries. Effective inter-country collaboration and sharing of experiences are paramount in developing emergency plans and preparing for adequate epidemic control measures.
The goal of malaria control is to prevent mortality and reduce morbidity and social and economic losses, through the progressive improvement and strengthening of local and national capabilities. Four basic technical elements of the malaria control strategy are: to provide early diagnosis and prompt treatment to plan and implement selective and sustainable preventive measures, including vector control to detect early, contain or prevent epidemics to strengthen local capacities in basic and applied research to permit and promote the regular reassessment of a country's malaria situation, in particular the ecological, social and economic determinants of the disease.
Effective implementation of the malaria control strategy requires: sustained political commitment from all levels and sectors of government malaria control to be an integral part of health systems, and be coordinated with relevant development programs in non-health sectors communities to be full partners in malaria control activities mobilization of adequate human and financial resources.
Malaria can be prevented by:
There is currently no malaria vaccine approved for human use. The malaria parasite is a complex organism with a complicated life cycle. Its antigens are constantly changing and developing a vaccine against these varying antigens is very difficult. In addition, scientists do not yet totally understand the complex immune responses that protect humans against malaria. However, many scientists all over the world are working on developing an effective vaccine. Because other methods of fighting malaria, including drugs, insecticides, and bed nets, have not succeeded in eliminating the disease, the search for a vaccine is considered to be one of the most important research projects in public health.
Symptoms of malaria include fever and flu-like illness, including shaking chills, headache, muscle aches, and tiredness. Nausea, vomiting, and diarrhea may also occur. Malaria may cause anemia and jaundice (yellow coloring of the skin and eyes) because of the loss of red blood cells. Infection with one type of malaria, Plasmodium falciparum, if not promptly treated, may cause kidney failure, seizures, mental confusion, coma, and death.
For most people, symptoms begin 10 days to 4 weeks after infection, although a person may feel ill as early as 7 days or as late as 1 year later. Two kinds of malaria, P. vivax and P. ovale, can relapse. In P. vivax and P. ovale infections, some parasites can remain dormant in the liver for several months up to about 4 years after a person is bitten by an infected mosquito. When these parasites come out of hibernation and begin invading red blood cells (“relapse”), the person will become sick.
No, not necessarily. Malaria can be treated. If the right drugs are used, people who have malaria can be cured and all the malaria parasites can be eliminated. However, the disease can persist if it is left untreated or if it is treated with the wrong drug. Some drugs are ineffective because the parasite is resistant to them. Some patients may be treated with the right drug, but at the wrong dose or for too short a period of time.
Two types (species) of parasites, Plasmodium vivax and P. ovale, have dormant liver stages that can remain silent for years. Left untreated, these liver stages may reactivate and cause malaria attacks ("relapses") after months or years without symptoms. Patients diagnosed with P. vivax or P. ovale are often given a second drug to help prevent these relapses. Another type (species), P. malariae, if left untreated, has been known to persist in the blood of some persons for several decades. But in general, if you are correctly treated for malaria, the parasites are eliminated and you are no longer infected with malaria.
Content source: National Center for Infectious Diseases, Division of Parasitic Diseases and the World Health Organization