Malaria overview

Malaria is preventable and treatable yet each year it still causes the deaths of an estimated half a million people, infects around 200 million and puts at risk over 3 billion people in 97 countries.

Malaria eradication is a complex task, targeting some of the poorest rural populations in developing countries where there is little existing infrastructure and often sparse healthcare services.

The Millennium Development Goal (Goal 6, Target 8) set a target to halt the spread of malaria by 2015 and begin to reverse the incidences of the disease. Following concerted action by WHO, governments and many agencies since 2000, the aims were achieved. In total an estimated 6.2 million deaths have been avoided by the malaria prevention measures, including distribution of around one billion insecticide treated mosquito nets in Sub-Saharan Africa.

The WHO Global Technical Strategy for Malaria 2016-2030 has set a further target to reduce incidence and mortality by 90%, eliminate malaria in at least 35 countries and prevent resurgence in all countries that are malaria free.

Malaria vectors

The mosquitoes that are capable of transmitting the malaria parasite to humans efficiently enough to cause significant illness all belong to the Anopheles genus. There are 41 Anopheles species that effectively transmit malaria. Only the female feeds on blood and can transmit the Plasmodium parasite.

The primary malaria vector species are those from Africa that are strongly anthropophilic, A. gambiae and A. funestus. These are responsible for the vast majority of malaria cases and deaths.

Vector control for malaria

Malaria is treatable, therefore vector control is just one part of a malaria elimination strategy that includes a healthcare programme involving detection, diagnosis and treatment of people.

For more information on healthcare strategy for malaria programmes see the WHO Strategy for malaria elimination in the Greater Mekong Subregion: 2015-2030.

This also describes different strategies used for malaria vector control, depending on whether the programme is at a reduction or elimination phase:

Transmission reduction phase

• Stratification of malaria situation: definition of major eco-epidemiological strata, with allocation of appropriate vector control by strata
• Vector control policy: Universal coverage of all at-risk populations with long-lasting insecticidal nets (LLINs) or indoor residual spraying (IRS) and supplementary measures where appropriate (eg long-lasting insecticidal hammock nets, larval source management, repellents) with special emphasis on mobile and migrant populations
• Entomological surveillance
• Monitoring and management of insecticide resistance
• Epidemic preparedness and response
• Research, technology, monitoring and evaluation: introduce a GIS-based database on malaria vector bionomics and insecticide resistance. Consider operational research on technical and operational feasibility, effectiveness and sustainability of current or new vector control approaches

Elimination phase

• Stratification of malaria situation: foci-based stratification, with categorization of active and potential foci
• Vector control policy: geographical reconnaissance. 100% coverage of all populations in active foci of malaria, with a view to interrupting transmission in a focus as soon as possible. Maintain universal coverage of at-risk populations with vector control in all areas in which malaria transmission has been interrupted
• Entomological surveillance
• Monitoring and management of insecticide resistance
• Epidemic preparedness and response
• Research, technology, monitoring and evaluation: a central repository of information related to entomological monitoring, and application of chosen vector control interventions established and fully functional

Malaria biology

Malaria in humans is caused by five species of the Plasmodium parasite:

• P. falciparum causes the most severe form of malaria as it multiplies rapidly in blood cells, causing severe blood loss. It can block blood vessels, including in the brain, causing cerebral malaria. It is common in tropical and subtropical areas and causes the highest rates of complications and deaths
• P. vivax is found in Asia, South America and parts of Africa. It is rare south of the Sahara where the Duffy negative blood group is common and people have resistance to infection. This species has dormant stages in the liver that can reactivate months or years after the first infection. It is one of the most common species worldwide
• P. ovale is similar to P. vivax, but can infect people with the Duffy negative blood group. It occurs mainly in West Africa and western Pacific Islands
• P. malariae uniquely has a three-day cycle (quartan) and can cause a lifelong chronic infection if not treated. It occurs worldwide
• P. knowlesi occurs in Southeast Asia, especially Malaysia, and has a 24-hour cycle. Its main host is macaques

Plasmodium lifecycle

The malaria parasite life cycle involves two host animals, humans and Anopheles mosquitoes. When an infected female mosquito bites a human to feed on blood it injects Plasmodium sporozoites into the human’s bloodstream.

• In the human: The sporozoites travel to the liver and infect the liver cells where they mature into schizonts. In P. vivax and P. ovale, these can have a long dormant stage, forming hypnozoites, which can last for months or years. The schizonts rupture and release merozoites into the blood where they invade red blood cells. The parasites multiply asexually in the red blood cells and are periodically released into the blood to infect more red cells. This stage causes the clinical symptoms of malaria, which is a reaction to the range of chemical released into the blood. Some of the merozoites differentiate into gametocytes, the sexual stages, which are ingested by mosquitoes on biting
• In the female mosquito: In the mosquito stomach the male gametocytes fertilise female gametocytes to form zygotes. The zygotes become elongated (called ookinetes) and enter the wall of the mosquito midgut where they transform into oocytes. These grow and develop sporozoites inside which are released and travel to the salivary gland, ready to be injected into a human during a bite

Malaria symptoms

The symptoms of malaria are similar to flu and vary greatly from none at all to very severe, including death. Travellers in a malaria risk area or up to one year after returning home, who become ill with fever or flu-like illness should seek medical attention. The most common symptoms include:

• Fever
• Sweats
• Chills
• Headaches
• Body aches
• Nausea and vomiting
• Weakness

The physical symptoms include:

• High temperature
• Enlarged spleen
• Enlarged liver
• Mild jaundice
• Increased respiratory rate

Severe cases of malaria can include:

• Cerebral malaria, which can produce abnormal behaviour, seizures and coma
• Severe anaemia due to loss of blood cells
• Haemoglobin (from destroyed red blood cells) in the urine
• Acute respiratory distress
• Acute kidney failure

For more details of the symptoms of malaria see the CDC malaria pages.

Malaria protection

If you are in a malaria risk area, WHO recommends that the main precaution is to prevent mosquito bites between dawn and dusk. Travellers may also need to take malaria prophylaxis medication before, during and after their travel, depending on the areas they will visit. There is currently no widely available vaccine for malaria, although several are under development and trials are being conducted.

Preventing mosquito bites

• Sleep under long-lasting insecticidal nets that reach the floor or are tucked into the mattress;
• Wear protective clothing, such as long sleeved shirts, long trousers, boots and hat. Clothing can also be treated with permethrin insecticide and repellents
• Stay in rooms with air conditioning and screens on windows and doors. Keep windows and doors shut
• Apply approved repellents such as DEET to bare skin and/ or clothing. The US EPA provides advice on choosing insect repellent products and lists those that have been tested to be effective. These products can produce adverse reactions therefore precautions must be taken when using them

Malaria medication

The US CDC recommends that travellers make an individual risk assessment to balance the need to take appropriate prevention measures with preventing adverse effects among those who do not need to take them.

This requires assessing the malaria risk in the country, city, region, type of accommodation, season, etc and the individual conditions such as pregnancy.

See the CDC advice for travellers for more information.

There are multiple options available for malaria medication in most countries. The choice will depend on existing medical conditions, medicines being taken, cost and potential side effects.

Anti-malarial drugs should also be bought from accredited pharmacies to ensure you are buying genuine products made to internationally accepted pharmaceutical standards.

See the NHS advice on antimalarial medication for more information.

The WHO has compiled a list of national travel and health websites.