Use of Antimalarials to Reduce Malaria Transmission

A number of strategies use antimalarial drugs to reduce transmission by clearing the affected population of malaria parasites. The best known of these is mass drug administration (MDA). MDA has been implemented in the past as part of attempts to eliminate malaria from an area and to respond to malaria epidemics caused by P. falciparum, the most lethal of the malaria parasites. MDA and related strategies that deploy antimalarials to reduce malaria transmission are described below.

Distribution of antimalarials in Italy in the 1930s. Attempts to control malaria through mass treatment with antimalarial drugs date back to at least the early 1930s. (Source: Archivio Casini, Sezione di storia della medicina, University of Rome 'La Sapienza')

Mass drug administration (MDA) is the treatment of the entire population in a geographic area with a curative dose of an antimalarial drug without first testing for infection and regardless of the presence of symptoms.

The World Health Organization does not currently recommend MDA for malaria for the following reasons:

1. Insufficient evidence to suggest an overall benefit. While MDA may result in a short-term reduction in malaria parasitemia among the population, a single administration has little impact on malaria transmission rates over time.
2. Promotion of drug resistance. Indiscriminant use of medicines for MDA may result in subtherapeutic (less than what is needed to clear parasites) levels of the drug in large numbers of persons, increasing the risk that malaria parasites will develop drug resistance.

Though not officially endorsed by WHO, MDA is being considered and tested as a strategy to reduce the burden of malaria with the goal of elimination. Strategies based on treating only those with symptoms will not reach those who are infected with parasites but have no symptoms, which is the case in many malaria-endemic areas.

Variations of MDA:

• Targeted mass drug administration (TMDA) is MDA implemented over a smaller high-risk area, such as a house, village, or hot spot.
• Intermittent preventive treatment (IPT), which is endorsed by WHO, is administration of a curative dose of an antimalarial drug to the entire population of asymptomatic individuals at discrete periods of time (frequently more than once). Various forms of IPT exist to address specific populations:
  • Pregnant women (IPTp)
  • Infants (IPTi)
  • Children (IPTc – also referred to as seasonal malaria chemoprevention [SMC])
  • School-going children (IPTsc)

Mass screening and treatment (MSAT) refers to screening all people in a population with an appropriate malaria diagnostic test and providing treatment to those with a positive test result. This intervention is based on the assumption that most of the people who can serve to infect mosquitoes will have high enough levels of parasites or antigen in their blood to be detected at the time of screening. Focal screen and treat (FSaT) is a variation of an MSaT performed in a smaller geographic area, such as a household, village, or hot spot.

Mass fever treatment (MFT), like MDA, refers to the treatment of malaria with a curative dose of an antimalarial drug within a well-defined population without testing, but unlike MDA, only persons with a fever are treated. MFT is a rapid measure that can be considered as part of an outbreak response. The criteria for choosing an antimalarial drug for MFT are the same as for the national policy for treating uncomplicated malaria (most likely an artemisinin-based combination therapy [ACT]). WHO states that mass treatment of fever cases with an ACT is appropriate as a strategy to reduce mortality once malaria has been established as the cause of the epidemic. This strategy aims to get treatment to people with probable malaria cases as quickly as possible to cure illness, avert death, and help contain the epidemic. After the outbreak response is more fully implemented in the community, laboratory confirmation of malaria parasites will precede treatment.

Both MSaTs and MFTs will reduce the number of persons receiving antimalarial drugs compared to MDA, thus theoretically reducing the number of adverse drug outcomes. MDAs will reach all infected persons, while MFTs will not reach those persons who are infected but asymptomatic, and MSaTs will not reach those persons for whom current field testing is not sensitive enough to capture (e.g. sub-microscopic infected persons). Thus, a role for MDA in elimination programs is being evaluated.