Malaria

What is it?

  • Malaria, a mosquito-born parasitic disease, is one of the world’s major killers. More than 212 million people had malaria in 2015, according to World Health Organization estimates, and 429,000 died. More than 90% of malaria deaths occur in Africa, and most are children under 5.
  • Four different species of microscopic malaria parasites can infect humans. The most dangerous is called Plasmodium falciparum; it occurs mostly in sub-saharan Africa and causes most deaths. Plasmodium vivax is less lethal but widespread in other parts of the world. The other two species are of minor public health importance.

Microscopic image of two Plasmodium falciparum cells in the blood smear of a patient. Credit: CDC/Dr. Mae Melvin

What are the symptoms?

Fever, headache, chills, and vomiting usually start between one and two weeks after someone has been bitten by an infected mosquito. Because those symptoms can be mild and similar to those of many other diseases, they’re often not recognized as malaria; that’s why good rapid diagnostic tests are so important. Malaria caused by Plasmodium falciparum can rapidly develop into a very severe disease, with severe anemia, respiratory distress, and cerebral malaria, an infection of the brain that is often fatal.

How does it spread?

  • Malaria spreads through the bite of female Anopheles mosquitoes. Some 30 Anopheles species are important as malaria carriers; the most widespread one is Anopheles gambiae, which causes most malaria cases in Africa. Mosquitoes become infected by biting a human who already has malaria. Malaria spreads more easily when mosquitoes live longer and in places where they have a strong preference to bite humans.
  • Having had malaria before gives you some immunity, especially against severe disease, but not total protection. Children and pregnant women are at higher risk because they have lower or no immunity.

How is it treated?

  • Many drugs have been developed against malaria. Currently, the recommended and most prescribed therapy is a so-called artemisinin-based combination therapy, or ACT. ‘Artemisinin’ refers to a class of drugs originally developed from a Chinese plant; in an ACT, these drugs are combined with another drug. A three-day course usually suffices to cure malaria.
  • Early diagnosis and immediate treatment are important to prevent malaria from becoming serious or life-threatening.
  • A key problem is that the parasite has quickly developed resistance against every drug that has become available so far. That means that many drugs have become useless. A big worry is that this will happen with ACTs, too, which would be a huge blow in the fight against malaria. Plasmodium falciparum is already becoming resistant ACTs in parts of South-East Asia. If resistance spreads to Africa, deaths from malaria could quickly rise. Other drugs are in the pipeline, but they will take years to bring to the market.
  • There is a huge international trade in fake and substandard drugs against malaria. This criminal activity is a major threat to public health. Fake and substandard drugs kill patients. Drugs that contain suboptimal doses can also elicit drug resistance in malaria parasites.

Coartem, produced by Novartis, is an artemisinin-based combination therapy (ACT), and one of the most widely used malaria treatments in the world. Credit: I.O. Ajayi et al, BMC Health Serv Res 2008

How can it be prevented?

  • One key strategy is using insecticide-treated bednets that keep mosquitoes away from people. They have been rolled out by the hundreds of millions in Africa and are one reason malaria deaths have declined the past decade.
  • Another strategy is so-called indoor residual spraying, in which walls of houses are covered with insecticides, protecting its residents for 3 to 6 months.
  • Both these approaches are under threat, however, because mosquitoes are becoming increasingly resistant to the most widely-used class of insecticides, the pyrethroids.
  • Drugs that can treat malaria can also help prevent it. For pregnant women living in areas with moderate or high malaria transmission, and for children under five in areas with high transmission, WHO recommends periodic treatment with a drug named SP. Travellers to areas where malaria occurs often taken drugs to prevent malaria as well.
  • Making a malaria vaccine has proven very difficult. One vaccine, called RTS,S or Mosquirix, and developed by pharmaceutical company GSK, has gone through extensive testing in kids in seven African countries, and will be rolled out in 3 countries as a pilot project starting in 2018. Unfortunately, it’s not a great vaccine. It prevents just over half of malaria cases in children aged between 5 and 17 months, and about a third in babies aged 6 to 12 weeks. Also, the vaccine’s protection begins to fade after a year or so.

Insecticide-treated bednets are an important malaria prevention tool. Credit: UNICEF/NYHQ2012-2185/Christine Nesbitt

What’s the outlook?

  • In 2007, Bill and Melinda Gates famously proposed the eradication of malaria worldwide. Most scientists say that is more a long-term aspiration than a plan. Although malaria cases have come down by 21% globally between 2010 and 2015, according to WHO, malaria remains a formidable enemy. Parasite resistance to drug, and mosquito resistance to insecticides, threatens to undo the gains. Around 90 countries still have malaria. Some have very few cases and can wipe out the disease. But stopping malaria in countries with high transmission rates seems impossible with the current tools.
  • Malaria experts agree that broad investment on many fronts is necessary. It includes new ways to control mosquitoes, such as odour-baited traps or genetically modified mosquitoes that can’t transmit malaria; new insecticides; close monitoring for drug resistance; new drugs; and new and more effective vaccines.

The malaria map has shrunk since 2000; green countries are no longer endemic.
Credit: WHO World Malaria Report 2016.

Connect to an expert on malaria

Resources

WHO’s fact sheet on malaria.

The 2016 World Malaria Report, which has lots of country-specific data about the fight against malaria.

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