Global Health: Malaria Overview

Global Health Headlines and Multimedia

Headlines
Video

Global Health Events

Calendar
Upcoming Events List

FAQs

Toolbox

  • What is malaria?

    • Malaria, common in many parts of the world, is a vector-borne disease of the blood caused by a parasite transmitted to humans by mosquitoes (the vector). Malaria can be fatal in some cases and people who have malaria are typically very sick with high fevers, shaking chills and flu-like symptoms. Although malaria is a preventable and treatable illness, it causes much morbidity (sickness) and mortality (death) worldwide, particularly in resource-poor regions.

  • Who is at risk of malaria?

    • Anyone can get malaria. However, most malaria cases occur among residents of countries where malaria is endemic (occurring on a constant basis), and among travelers to those countries. In non-endemic countries, malaria can occur among non-travelers in the form of congenital malaria (malaria passed from an infected mother to her child during pregnancy or birth), introduced malaria (malaria introduced in a non-endemic malaria region by an infected host), or transfusion-related malaria (malaria acquired during blood transfusions).

  • Who is most at risk of severe and fatal malaria?
    • People who are exposed to the bites of mosquitoes infected with P.falciparum -- the parasite that causes the most severe and life-threatening cases of malaria -- are most at risk of dying of malaria. P.falciparum is very common in many countries in sub-Saharan Africa. People who have little or no immunity to malaria -- such as young children and pregnant women -- or people who travel from areas with no malaria to areas where malaria is endemic are more likely to become severely ill and die. Impoverished people living in rural areas who lack education, money or access to health care are more vulnerable to the disease. As a result of all these factors, an estimated 90% of deaths caused by malaria occur in sub-Saharan Africa, and most of these deaths occur among children younger than five years old.
  • What are the signs and symptoms of malaria?

    • People with malaria typically have periods of chills, fevers and sweating that recur every one, two or three days. When the malaria parasites infect a person's red blood cells, the person's temperature rises and the person feels hot. Then, when infected red blood cells burst, the person feels cold and shivers. Nausea, headache, fatigue, muscle pain, vomiting and diarrhea often accompany the fever. These symptoms often are mistaken for influenza or gastrointestinal infections. The destruction of red blood cells also can cause jaundice (yellowing of the skin or whites of the eyes) and anemia (a lower-than-normal level of red blood cells). Infection with P.falciparum, if not promptly treated, might lead to kidney failure, seizures, mental confusion, coma or death.

  • How is malaria detected?

    • Malaria is difficult to diagnose under the best circumstances. Definitive diagnosis is based on the observation through a microscope of parasites in the red blood cells. Newer diagnostic tools include fluorescent staining, genetic probes and antigen detection in the form of a dip stick, but these methods are not widely used. Therefore, the most important diagnostic tool for much of the world remains the recognition of malaria symptoms, which include fever, chills, headaches, nausea, profuse sweating, muscle pain, and fatigue.

  • How soon will a person feel sick after being bitten by an infected mosquito?

    • For most people, the incubation period of malaria -- the time between infection and the first appearance of clinical signs, usually fever -- is about 10 days to four weeks after being bitten by an infected mosquito.  However, that period might be shorter or longer, depending on the infecting species (shortest for P.falciparum, longer for P.malariae).

      In the case of P.falciparum malaria, which can be fatal, symptoms may develop at any time between one week after the first possible exposure to malaria and two months (or even longer in exceptional cases) after the last possible exposure.

      People with P.malariae who are untreated or partially treated might not have symptoms for many years and can become carriers of the parasite for life.

      Two kinds of malaria, P.vivax and P.ovale, can relapse, and some parasites can remain dormant in the liver for several months up to about four years after a person is bitten by an infected mosquito. When these parasites come out of hibernation and begin invading red blood cells, the person will become sick.

      When malaria infection occurs by blood transfusion, the time to the start of symptoms depends on the number of parasites in the transfusion.

  • How long is a person with malaria infectious after onset of symptoms?

    • In P.vivax and P.ovale infections, the person is almost immediately infectious to mosquitoes after the onset of symptoms. In P.falciparum, a person is infectious to mosquitoes after several days, when mature malaria parasites appear in the bloodstream.

      Antimalarial drugs, such as chloroquine and mefloquine, that are given to cure malaria infections do not eliminate mature P.falciparum parasites from the bloodstream. A person who has been successfully treated with malaria drugs therefore might be healthy but infectious for several weeks until the parasites naturally die off, or until another drug, such as primaquine, that does eliminate the parasites is administered.

      Some people living in highly endemic areas, such as in parts of Africa, have developed immunity to malaria after being infected repeatedly because their bodies have created natural antibodies to the parasite. Although these people might not develop symptoms, they do carry parasites in their blood that can infect mosquitoes that bite them.

  • Can a survivor transmit malaria to others after she or he has fully recovered?
    • Yes, a person who no longer displays the symptoms of malaria infection can still transmit the parasite to others through mosquitoes. For example, a person who does not develop symptoms because of a built up immunity to the P.falciparium parasite, or a person who has recovered from a primary infection of P.vivax or P.ovale can transmit the parasite to mosquitoes. This is because, in these cases, the malaria parasites are still alive in the bloodstream of the infected individual for an average period of two months from the date of infection, after which the parasites die off naturally, unless specific powerful malaria drugs are administered to kill these parasites. When an uninfected mosquito takes a blood meal from such an infected asymptomatic person, the parasites are transferred from the infected person to the mosquito and the mosquito then becomes a vector for the disease.
  • If a person survives malaria infection does he or she develop immunity?

    • A person who survives malaria infection might be immune to subsequent infection, but only partially and for a time period that is related to the intensity and frequency of previous infections. In areas where malaria infection is infrequent, people might never build up enough immunity to protect them from infection. In areas where malaria is endemic and prevalence of the disease is high, newborns are protected in their first months of life by the antibodies of their immune mothers. If they do not die of malaria or other causes, children gradually develop their own immunity over the years. However, immunity to malaria is reversible, and fully immune adults who leave malaria-endemic areas commonly return to a state of non-immunity over a period of one to two years.

      Some people have genetic traits that make them immune to malaria infection by preventing the parasites from growing and developing normally. Sickle-cell anemia and thalassemia are two inherited blood disorders that are associated with malaria immunity. People with two sickle-cell anemia or thalassemia genes often become seriously ill from these disorders and die in childhood if untreated. However, people who have only one sickle-cell or thalassemia gene do not develop the genetic disorder and are resistant to malaria. Various sickle-cell or thalassemia genes are widespread among people in Africa, the Mediterranean region, the Middle East, India, and Southeast Asia.

  • What complications can result from malaria?
    • Malaria caused by P.falciparum can cause kidney or liver failure, coma or death. Although infections with other malaria parasites cause less serious symptoms, parasites can remain inactive in the liver and cause symptoms months or even years after infection.
  • Which parts of the body does malaria usually infect?

    • Mosquitoes inject the malaria parasites into small blood vessels in the skin. From there they travel through the bloodstream to the liver, where they develop and multiply in liver cells before again entering the bloodstream and invading other body systems in order to reproduce further. Other internal organs, including the brain, can be affected.

  • How common is malaria?

    • The World Health Organization estimates that nearly 250 million cases of malaria and about one million deaths from malaria occurred in 2006. More than 80% of malaria cases occur in African countries.

      Malaria is a public health problem in more than 100 countries and about half of the world's population is at risk for malaria infection-- or more than three billion people. The disease is a leading cause of death in lower-income countries and for children worldwide; it is estimated that a child dies of malaria every 30 seconds. The majority of malaria deaths occur among young children in Africa, especially in remote rural areas with poor access to health care services. Other high-risk groups include pregnant women, non-immune travelers, refugees, displaced persons and migrant workers entering endemic areas.

  • Is there a vaccine for malaria?

    • Currently, there is no malaria vaccine approved for human use. The malaria parasite is a genetically complex organism with a multifaceted life cycle. The parasite is constantly changing within the human host and therefore, developing a vaccine against malaria has been and continues to be very difficult. In addition, scientists do not yet completely understand the complex immune responses that naturally protect some humans from malaria infection.  The development of a malaria vaccine is considered to be one of the most important research projects in public health because other methods of fighting the disease -- including drugs, insecticides and bed nets -- have not succeeded in eliminating it. Although various approaches to a malaria vaccine are currently under study, none are expected to be commercially available anytime soon.

  • How can malaria be prevented?
    • Protection from mosquito bites is the first line of defense against malaria in endemic areas. However, malaria can also be prevented by utilizing antimalarial prophylactic medications. In general, malaria can be prevented by:
      • Keeping mosquitoes from biting you, especially at night;
      • Taking antimalarial drugs to kill the parasites;
      • Wearing insect repellent that contains 20% to 35% DEET (N,N-diethylmethyltoluamide) or dimethyl phthalate on exposed skin;
      • Wearing long-sleeved shirts and long trousers if outdoors between dusk and dawn;
      • Destroying places where mosquitoes breed;
      • Spraying insecticides, using insecticide dispensers that contain tablets impregnated with pyrethroids, or burning pyrethroid mosquito coils indoors at night;
      • Sleeping under bed nets, which are especially effective if they have been treated with the insecticide permethrin; and
      • Seeking medical treatment if travelers experience an unexplained fever while in or after returning from an area where malaria is common.
  • Will taking antimalarial medications prevent infection?

    • While no antimalarial prophylaxis drug regimen provides complete protection from malaria infection, it can reduce the risk of infection. Medicines to prevent malaria are usually prescribed for persons traveling to areas where malaria is common. Travelers from different countries might receive different recommendations because of differences in the availability of medicines.

      Travelers visiting only cities or rural areas where there is no risk of malaria might not need preventive drugs. An exact itinerary is needed to decide on the right degree of protection. The type of prophylaxis depends on the area, local species of malaria, local pattern of antimalarial drug resistance and personal characteristics -- such as allergies and contraindications. Additionally, recommendations concerning prophylaxis and treatment for malaria may vary for some populations, including pregnant women and children.

  • Can children take prophylactic malaria pills?

    • Children of any age can get malaria and any child traveling to a malaria-endemic area is at risk for the disease. Although children can take malaria pills, it is important to note that some antimalarial medications are not suitable for them, and that medication dosing is different for children compared to adults.

  • What is the treatment for malaria?

    • Malaria can be treated with drugs. The type of drugs and length of treatment depend on which kind of malaria is diagnosed, the geographic location where the patient was infected, the patient's age and how severely ill the patient is at start of treatment. Currently, the standard treatment for malaria includes:
      • Chloroquine
      • Sulfadoxine-pyrimethamine
      • Mefloquine
      • Atovaquone-proguanil
      • Quinine
      • Doxycycline

      In most cases, if these drugs are used, people who have malaria can be cured and all the parasites in their bloodstream can be eliminated in time. However, the disease can persist if it is left untreated or if it is treated with the wrong medications. In addition, with improper adherence to treatment protocols, some malaria parasites can become resistant to certain drugs, which render the drugs ineffective. Some people may be treated with the correct drug but at the wrong dose or for too short a period of time, which can again result in under-treatment of the disease and persistence of the parasites.

      Two types of malaria parasites, P.vivax and P.ovale, have dormant life cycle stages in the human liver and might not cause symptoms for years. Left untreated, these dormant parasites might reactivate and cause malaria relapses after months or years without symptoms. People diagnosed with P.vivax or P.ovale malaria often are given a second drug to help prevent relapses. Another species, P.malariae, has been known to persist in the blood of some persons for several decades if left untreated.

      Because of the unprecedented scale of multi-drug resistant malaria strains -- especially in South and Southeast Asia, South America and Africa -- the World Health Organization currently recommends that countries with MDR strains implement artemisinin-based combination therapies as a first-line of treatment However, in countries unable to implement ACTs, WHO recommends the use of amodiaquine plus sulfadoxine/pyrimethamine combination therapy.

  • When should malaria be treated?

    • Malaria should be treated as early as possible in the course of the disease, before it becomes severe and poses a risk to the person's life. Several malaria drugs are available, and the drugs should be administered early in infection.

  • What are artemisinin-based combination therapies (ACT)?

    • Artemisinin compounds are a group of malaria medications that produce a very fast response in people with malaria, are active against multi-drug resistant P.falciparum malaria, are well tolerated by people who have malaria and have the potential to reduce malaria transmission by decreasing parasite carriage in the bloodstream. Artemisinin compounds -- including artesunate, artemether and dihydroartemisinin -- are usually used in combination with other antimalarials to treat the parasite.  These combinations are called artemisinin-based combination therapies, or ACTs.

      Many countries in Africa have switched to using ACTs as a first-line therapy against malaria because of the emergence of drug-resistant parasites. Because artemisinin compounds are derived from a substance extracted from the plant Artemisia annua, the cultivation of the plants and production of the drugs takes at least eight months.  The recent increased demand for the drugs must be considered in order to avoid supply shortages. Furthermore, while ACTs are considered a first-line therapy against drug resistant parasites, early evidence suggests that resistance to ACTs may be occurring in parts of Asia.

  • Is drug-resistant malaria a problem?

    • Malaria that is resistant to malaria drugs has been linked to increased malaria-related morbidity and mortality and continues to be an important public health challenge, particularly among countries in South and Southeast Asia and South America. There is also a growing concern about the emergence of malaria drug resistance in parts of Africa.

      Thus far, drug resistance has been confirmed in only two of the four human malaria parasite species: P.falciparum and P.vivax. Chloroquine resistant P. falciparum (CRPF) first emerged as a major problem in Southeast Asia, Oceania, and South America in the late 1950's and early 1960's. Since then, chloroquine resistance has spread to nearly all areas of the world where P.falciparum malaria is transmitted. P.falciparum has also developed resistance to nearly all of the other currently available malaria drugs, such as sulfadoxine- pyrimethamine, mefloquine and quinine. Chloroquine resistant P.vivax (CRPV) malaria was first identified in 1989 and has now been found in Southeast Asia, the Indian subcontinent, and South America.

      Administering two or more malaria drugs can improve treatment outcomes and help reduce the risk of the parasite developing resistance to the individual drugs in the combination. The World Health Organization recommends that all countries experiencing cases of malaria that are resistant to at least one drug use combination therapies.

  • How can malaria be controlled?

    • The goal of malaria control is to prevent illness and death from malaria, as well as prevent social and economic losses, by improving and strengthening local and national capabilities. Basic technical elements of a malaria control strategy are:

      • To provide early diagnosis and rapid treatment;
      • To plan and implement selective and sustainable preventive measures, including the control of mosquitoes that transmit malaria;
      • To detect early, contain or prevent epidemics; and
      • 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.
      The successful implementation of a 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 coordinated with relevant development programs in non-health sectors;
      • Communities to be full partners in malaria control activities; and
      • The mobilization of adequate human and financial resources.

  • Has malaria eradication been attempted?

    • A malaria eradication campaign was begun in the 1950s, but the program failed because of administrative issues and the development of insecticide-resistant mosquitoes and drug-resistant malaria parasites. In addition, the campaign did not include most African countries, where malaria is most common.

      Although malaria has been eradicated from many developed countries with temperate climates, the disease remains a major public health problem in many developing countries and in tropical and subtropical parts of the world.

      International efforts to address malaria have intensified in recent years and the U.N. Millennium Development Goals include targets to reduce the impact of malaria by 2015.

  • Is malaria a serious disease?

    • Malaria is a leading cause of death and illness worldwide, especially in developing countries. Most deaths occur among young children. Malaria has a significant impact on the economies of the most affected countries because it results in so much illness and death, facilitating a cycle of disease and poverty in already resource-poor nations.

  • Is quarantine required or permitted as a preventive measure?

    • No. Quarantine is the separation and containment of uninfected individuals who have been, or may have been, exposed to an infectious agent in order to limit or prevent exposure to individuals who have not been exposed.

  • Is quarantine required or permitted as a preventive measure?

    • No. Isolation is the separation and confinement of infected individuals, or those likely to be infected, in order to limit or prevent exposure of an infectious agent to uninfected individuals.

  • Are vaccinations or any other treatment measures required or recommended for international travel?

    • No malaria vaccine currently is available. However, it is recommended that people traveling abroad to regions where malaria is present speak with a health professional about prophylactic antimalarial drug regimens that can reduce the risk of infection.

  • Where does malaria commonly occur?

    • Malaria most commonly is found in warmer regions of the world that have tropical and subtropical climates. Anopheles mosquitoes thrives in higher temperatures, and malaria parasites, which grow and develop inside mosquitoes, need warmth in order to grow to a maturity stage in which they can be transmitted to humans.

      Malaria can occur in more than 100 countries and territories, putting half of the world's population at risk of contracting the disease. Large areas of Central and South America, Hispaniola (Haiti and the Dominican Republic), Africa, the Indian subcontinent, Southeast Asia, the Middle East and Oceania are considered malaria-risk areas.

      However, 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.

      The risk to travelers to places where malaria occurs varies depending on local weather conditions, the number of mosquitoes in the area and the traveler's itinerary, including the time and type of travel.

  • Why is malaria so common in Africa?
    • In sub-Saharan Africa, the primary malaria mosquito, Anopheles gambiae, transmits malaria very efficiently. In addition, the type of malaria parasite most commonly found in this region, P. falciparum, causes severe, potentially life-threatening disease. In addition, economic problems and political instability in the region may also present challenges to the development of effective malaria control programs. Finally, malaria parasites in the region are becoming more resistant to malaria drugs such as chloroquine, presenting another barrier to malaria control in Africa.
  • What has caused malaria epidemics to end in past occurrences?

    • Malaria transmission rates can naturally slow down due to a decline in the density of mosquitoes in an area and a lull in their breeding behaviors. However, in the past, human interventions have mainly controlled malaria epidemics. For example, in regions with temperate climates, the spraying of DDT and other insecticides thwarted the spread of malaria. Controlling a malaria epidemic, in general, involves treating acute infections in humans and preventing the further transmission of the disease and future recurrences of the epidemic.

      If uncontrolled, malaria epidemics follow a natural course.  The epidemic spreads in a series of stages related to the incubation interval (the time period between the development of infective malaria parasites in the primary case and the parasites' reappearance in a secondary case). This incubation period 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 transmission, which is much faster in P.vivax epidemics than in P.falciparum epidemics for example. In areas where both P.vivax and P.falciparum are present, the initial stages of an epidemic are determined by the prevalence of P.vivax infections and a very gradual increase in severity of the epidemic.  However, in later stages of the epidemic, P.falciparum likely would be more prevalent.
       
      The peak of new infections in a P.falciparum epidemic would be achieved when about 50% of the at-risk population is infected, unless other factors, such as climate changes (for example, from hot weather to colder temperatures), prevent further transmission.

  • What are the conditions that would lead to a major epidemic?

    • Malaria epidemics occur when non-immune and partially immune populations are exposed to infected mosquitoes at high rates. Potential epidemic situations usually can be identified by examining the malaria situation in an area, including general aspects of the geography, history and socio-economic situation. Potential epidemic situations include:

      • Areas of unstable malaria where environmental conditions for malaria transmission change (for example, increased rainfall and temperature);
      • Areas where the level of endemic malaria has been reduced because of widespread treatment and/or malaria control programs but where the malaria situation has become unstable because the programs no longer can be sustained;
      • Situations where non-immune populations migrate into an endemic area, such as refugee movements or migration of laborers;
      • Situations where persons carrying malaria parasites migrate into a non-endemic but malaria-amenable area where Anopheles mosquitoes live or other environmental factors favor malarial transmission; and
      • Situations in which a potential epidemic is not properly controlled through sufficient health care services and malaria control programs.

      In areas where a potential for a malaria epidemic exists, health care and prevention services should rapidly be prepared to offset a potential epidemic. Many epidemic-prone areas transcend national borders, so effective cross-country collaboration is important in developing emergency response plans and preparing adequate epidemic control measures.

  • What is the infectious agent that causes malaria?
    • Malaria is caused by any one of four species of one-celled parasites, called Plasmodium. The parasite is spread to people by the female Anopheles mosquito, which feeds on human blood. The four types of malaria parasites that can infect humans are Plasmodium falciparum (P.falciparum), Plasmodium vivax (P.vivax), Plasmodium ovale (P.ovale), and Plasmodium malariae (P.malariae). Infection with any of the malaria species can make a person feel very ill, but infection with P.falciparum is potentially life-threatening if not treated promptly. Although malaria can be a fatal disease, illness and death from malaria are largely preventable.
  • How do the known varieties differ?
    • The four Plasmodium species that cause human malaria differ morphologically, immunologically, in geographical distribution, relapse pattern and drug response. Although there are nearly 120 species of Plasmodia known to exist, only four species cause malaria in humans. P. falciparum causes the most serious disease.
  • When was malaria first identified?

    • Malaria, as it is defined today, was first identified in the late 1800s. In 1880 Alphonse Laveran, a French army surgeon working in Algeria, first saw and described parasites in the red blood cells of a man showing symptoms of malaria. Six years later, Camillo Golgi, an Italian neurophysiologist, established that there were at least two forms of the malaria. In August 1897, Ronald Ross, a British officer in the Indian Medical Service, demonstrated that malaria parasites could be transmitted from infected patients to mosquitoes. Laveran, Golgi and Ross were all awarded the Nobel Prize for their discoveries in 1907, 1906, and 1902 respectively.

  • Is malaria an emerging infectious disease?

    • Yes. Many countries recently have experienced resurgence in cases caused by P.falciparum, the most deadly of the four human malaria parasites. Urban migration, poverty and poor sanitation have helped malaria return to cities where it once was eliminated. New roads, logging and irrigation have attracted people to once-isolated areas where malaria-transmitting mosquitoes thrive. In addition, refugees, migrants and tourists have spread the disease across borders.

      The resurgence of malaria is worsened by the spread of parasites that are resistant to malaria medications. Like bacteria and viruses, parasites can develop resistance to the drugs used to prevent or treat infection. Today, malaria parasites are increasingly resistant to chloroquine, the drug most widely used for malaria prevention and treatment. Chloroquine-resistant malaria strains have been reported in Africa, Asia and the Americas. There is also early evidence that resistance to artemisinin-based combination therapy (ACT), a newer group of malaria medications that are used to treat multidrug- resistant P.falciparum malaria, may be occurring in parts of Asia.

  • How is malaria transmitted?

    • Malaria is not transmitted from person to person like a cold or the flu. A person cannot get malaria from casual contact with people infected with malaria.

      A person can get malaria from the bite of an infected female Anopheles mosquito, primarily between sunset and sunrise. Only Anopheles mosquitoes can transmit malaria, and they must have been infected by the malaria parasite through a previous blood meal taken from an infected person.

      When a mosquito bites a person who has malaria, the insect takes in a small amount of blood that 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 feeds on the blood of a human, the parasites mix with the mosquito's saliva and are injected into the human's bloodstream.

      Once in the blood, the malaria parasites travel to the liver and enter liver cells to grow and multiply. During this incubation period, the infected person has no symptoms. After a few days or as long as several months, the parasites leave the liver cells and enter red blood cells. Once in the cells, the parasites 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 symptoms of malaria, including fever, chills and other flu-like symptoms.

      Because the malaria parasite is found in red blood cells, malaria also can be transmitted through blood transfusion, organ transplant, or the shared use of needles or syringes with malaria-infected blood. Malaria also can be transmitted from a pregnant woman to her fetus before or during delivery -- called congenital malaria.

  • Is malaria airborne?

    • Not in the usual sense of the word. Malaria is not transmitted from person to person like a cold or the flu. People get malaria from the bite of a mosquito that is harboring the Plasmodium parasite. Mosquitoes fly in order to reach sources of blood they need to survive, and this is how malaria is transmitted.

      Large numbers of Anopheles mosquitoes usually are not found more than two to three kilometers from their breeding places. However, strong seasonal winds may carry Anopheles up to 30 km from their main breeding place. Occasionally, cases of malaria are detected near airports in non-endemic areas because infected mosquitoes from endemic zones are carried in on aircraft.