How do molecular markers affect treatment?

Molecular markers can be powerful tools for surveillance of drug sensitivity and assessing the need for changes in antimalarial policy. Sample collection and molecular analysis of resistance markers is relatively rapid and inexpensive. These simple methods make molecular markers useful indicators to guide antimalarial treatment in situations ranging from emergencies and outbreaks to large-scale evaluations of marker prevalence.

Although molecular markers can be very useful in informing antimalarial policy, examples of real world application remain rare. Part of the problem is the lack of mechanisms for timely and meaningful sharing of molecular data among researchers, National Malaria Control Programmes and policy makers.

To strengthen the practical value of resistance markers in public health, the WWARN Molecular Module aims to:
•    Facilitate communication of molecular marker information with non-scientists by providing tools for presentation and analysis of data.
•    Provide up-to-date summary information on molecular markers at a country and regional level.
•    Share WWARN tools with National Malaria Control Programmes and policy makers.
•    Raise awareness of the utility of molecular markers in studying antimalarial resistance.

Molecular markers in action

In Mali
The application of molecular monitoring to public health was demonstrated in Mali (Djimde et al 2004), where an outbreak of malaria occurred in a region of limited infrastructure and civil unrest in 1999. An epidemic investigation team collected filter paper blood samples from patients in the area and analyzed them for molecular markers within a few days. Molecular assays revealed an unexpectedly high prevalence of resistance to chloroquine but not to SP (Fansidar). Based on these results, chloroquine, the first line treatment at the time, was successfully replaced by SP. Because molecular markers of resistance were evaluated in real time, the population was effectively treated with an appropriate drug.

In Tanzania
A replacement first-line therapy for the failing chloroquine was needed in the late 1990s. Molecular markers for SP resistance were surveyed in several sites throughout the country to determine the potential efficacy of SP should the drug be deployed next (Mugittu et al 2004). Investigators found that SP would be more effective than chloroquine in the short-term, but the baseline prevalence of molecular markers indicated that its efficacy would soon be compromised by increasing resistance. As a result, the Ministry of Health adopted SP as the best-available interim treatment, but actively sought out another regimen and eventually switched to artemether-lumefantrine.