How is malaria treated and prevented?

How is malaria treated?

• If malaria is diagnosed and treated quickly, most people will fully recover.
• Treatment of malaria depends on many factors including:
  • the severity of the disease
  • the species of malaria parasite that has caused the disease (for example, Plasmodium falciparum)
  • the part of the world the infection was acquired
  • whether preventative antimalarial tablets were taken.
• Drugs that kill the parasite that causes malaria can be used to treat and prevent the disease. These drugs are called antimalarials.
• However, if you contract malaria while taking one type of antimalarial drug, the same drug cannot be used to treat the infection as the parasite may be resistant to it.
• Different drugs target different features of the parasite’s biology and life cycle. For example, chloroquine targets the blood stages of the life cycle whilst primaquine removes the dormant liver stages.
• Because of this, drugs are often used in combination with each other to make sure the malaria parasite is removed from all areas of the body. For example, primaquine can be used along with chloroquine to treat Plasmodium vivax.
• Combinations of drugs are also used to try to prevent the parasite from developing resistance to the individual drugs on their own. This is the strategy used in artemisinin combination therapy (ACT), which uses an artemisinin-based drug plus one partner drug. ACT is currently the front-line treatment for Plasmodium falciparum malaria.
• If any parasites are left in the body after treatment, the disease may return. For example, Plasmodium vivax and Plasmodium ovale are able to lie dormant and hidden in the liver even if the parasite has been cleared from the rest of the body. If the parasite isn’t cleared properly from the liver the disease can return months or even years later.
• Partial immunity can be developed over years of exposure to the disease and although it never develops into full immunity it can reduce the severity of disease and risk of death from malaria.
• Most malaria deaths occur in young children under five years whose bodies have not had a chance to develop any immunity to the parasite.

A blood sample being smeared on a slide before being examined under the microscope to look for evidence of the malaria parasite.
Image credit: Shutterstock

How can malaria be prevented?

Drugs

• Antimalarial drugs can also be used to prevent malaria. This is known as chemoprophylaxis.
• Chemoprophylaxis kills the blood stage of the malaria parasite and consequently prevents the symptoms of the disease.
• If travelling to an area where there is a risk of catching malaria it is very important to take antimalarial drugs because they can reduce that risk of developing malaria by up to 90%.
• The type of antimalarial drugs prescribed will depend on a number of factors including:
  • where the individual is travelling (in some areas the parasites are resistant to certain drugs)
  • family history
  • medical history
  • age
  • pregnancy.
• Frequently prescribed preventative antimalarials include doxycycline, chloroquine and a combination of atovaquone and proguanil.
• However, some antimalarials can only be used in certain areas of the world because parasites are resistant to some drugs. For example, chloroquine can only be used to prevent Plasmodium falciparum in regions of South America because Plasmodium falciparum is completely resistant to chloroquine in Africa and Asia.
• Most courses of antimalarials have to be started before entering the region affected by malaria. This allows the medicine to increase to the effective levels in the body. It also gives time to check for any side-effects before travelling.
• A person will need to continue taking the antimalarials after returning home to cover the incubation period of malaria.
• For pregnant women living in moderate to high-risk malaria areas, intermittent preventative treatment (IPT) is given. This means they are given antimalarial drugs at regular intervals during their pregnancy, usually at each antenatal visit after the first trimester.
• Malarial infection during pregnancy is a major public health problem. It can cause severe malaria in the mother and lead to premature delivery and low-birth-weight in their baby.
• IPT could benefit around 32 million pregnant women in sub-Saharan Africa each year. It has, however, proven difficult to encourage health workers to administer it to pregnant women.
• During the seasons when malaria transmission is high, infants living in moderate to high-risk areas are usually given a monthly course of antimalarials alongside their routine medical care.

Child receiving artemisinin combination therapy (ACT).
Image credit: Bonnie Gillespie

Vaccines

• In mid-2015 the world’s first malaria vaccine Mosquirix (also known as RTS,S) was given the green light for use against Plasmodium falciparum malaria in Africa.
• The vaccine works by preventing the malaria parasite from entering the liver where it can mature and multiply to cause disease symptoms.
• Although the long-term protection provided by the vaccine has still not been determined, the best protection has been observed when the vaccine was given to children aged five to 18 months in three doses given a month apart, followed by a booster dose after 20 months.
• The booster dose was found to be crucial as the effectiveness of the vaccine reduced over time.
• The vaccine is not considered a ‘magic bullet’ against malaria but is an important building block towards the development of future malaria vaccines.

Vector control

• Anopheles mosquitos are vectors for malaria. This means that they transmit the disease from one human or animal to another.
• Vector control of malaria refers to any method to limit or eradicate malaria-carrying Anopheles mosquitos.
• Vector control is one of the most effective ways of controlling malaria.
• Indoor residual spraying (IRS) involves spraying insecticide (a substance that kills insects), once or twice a year, on all indoor surfaces where mosquitoes are likely to rest. This has been found to reduce the survival of mosquitoes that enter the home. It is estimated that 5% of at-risk populations are protected by this method of vector control.

Carrying out indoor residual spraying in Ghana. Image credit: Navrongo Health Research Centre, Ghana; Will Hamilton

• Long-lasting insecticidal nets (LLIN) are mosquito nets that are also sprayed with an insecticide. They provide a physical and chemical barrier to the mosquito vector at night, when the mosquito is most likely to bite. The nets also result in large-scale killing of mosquitoes when used by entire communities.

A mosquito net hung over a bed to help protect against mosquito bites during the night.
Image credit: Shutterstock

• Larviciding involves treating the breeding sites of the mosquito with substances that kill the larval stages of the insect. It is effective, but only in areas where mosquito breeding sites are fixed in one place and easy to find.

Major challenges in malaria control

Drug resistance

• Currently, three of the five malaria parasite species known to affect humans have developed resistance to antimalarial drugs. These are Plasmodium falciparum, Plasmodium vivax and Plasmodium malariae.
• If a malaria parasite becomes resistant to an antimalarial drug, the drug takes longer to kill all the parasites in the body and it takes longer for the patient to stop having the symptoms of malaria.
• In some cases the drug may be completely ineffective and fail to remove all of the parasites from the body.
• The problem of drug resistance is further complicated by a process called cross-resistance. This is when resistance to one drug also enables the parasite to be resistant to another drug that works by a similar mechanism.
• Cross-resistance has resulted in several antimalarials being removed from the drug market altogether because they are no longer effective.
• The emergence of Plasmodium falciparum resistant to a key drug called artemisinin is a major public health concern.
• Artemisinin combination treatments (ACTs) have been integral to the recent successes in global malaria control. But, resistance to these treatments has emerged independently in South-East Asia and is now spreading across that region.
• Resistance to previous generations of antimalarials spread rapidly around the world so in January 2011 the World Health Organization (WHO) released a global plan to:
  • Contain or eliminate artemisinin resistance where it is already a problem.
  • Prevent artemisinin resistance where it has not yet become a problem.
• If artemisinin resistance becomes widespread in Africa, as has happened with other antimalarial drugs such as chloroquine, then the public health consequences would be catastrophic and it is likely there would be a reversal in the recent declines seen in malaria mortality.
• Scientists are using whole genome sequencing and other techniques to investigate which genetic changes are responsible for artemisinin resistance in Plasmodium. Finding these genetic changes could enable scientists to track and hopefully prevent the spread of resistance.

A map showing the spread of chloroquine resistance in countries with Plasmodium falciparum from 1957 to 2005. (Data sources:Worldwide Antimalarial Resistance Network;WHO World Malaria Report, 2014).
Image credit: Genome Research Limited

Insecticide resistance

• Insecticide resistance is the ability of an insect to survive and multiply despite exposure to an insecticide designed to kill it.
• Insecticide resistance in Anopheles mosquitos is a challenge in malaria vector control.
• Similar to how malaria parasites become resistant to antimalarial drugs, insecticide resistance occurs when a genetic mutation occurs in the mosquito’s DNA enabling it to survive contact with a specific insecticide.
• This resistance can then spread when the surviving mosquitos breed, passing on the genetic mutation and producing more resistant mosquitos.
• Insecticide resistance in Anopheles mosquitos has been detected in around 64 countries around the world.
• If left unchecked, insecticide resistance could lead to a substantial increase in the number of cases of malaria and deaths.
• Strategies are being developed to ensure that different insecticides are rotated frequently to avoid the mosquitos becoming resistant to them. It is also hoped that new and innovative tools to control the numbers of mosquito vectors can be developed.
• Scientists are also carrying out whole genome sequencing on mosquito populations to identify exactly which genes are involved in insecticide resistance.

Insecticide resistance in Anopheles mosquitos is a challenge in malaria vector control.
Image credit: Shutterstock