Plasmodium falciparum msp1, msp2 and glurp allele frequency and diversity in sub-Saharan Africa

A study done across five sub-Saharan countries provides new evidence on how to assess the efficacy of antimalarial drugs

Malaria Journal 2011, 10:79 doi:10.1186/1475-2875-10-79
8 July 2011

The study was done to support a recommendation from the World Health Organization that patients receiving treatment for malaria be monitored to ensure that the patient is not still infected with the parasites that cause the disease. If an infection is detected, it must be determined whether it is the original infection, (and is therefore not responding to treatment), or whether the patient has become reinfected. But figuring out whether an infection is the original one or a new one can be challenging.

In this study, follow-up exams were done over a period of 28 days, (although it could be done over a longer period, depending on the type of medication the patient had been receiving). The probability of being reinfected depends on the duration of follow-up, the intensity of malaria transmission, and the drug’s residence time in the body. As medication levels in the blood decline, they gradually become ineffective in suppressing parasites, whether from a new or the original infection.

Figuring out whether an infection is new or the remains of the original infection is crucial to assessing the efficacy of treatments. The test used to distinguish between old and new infections is the Polymerase Chain Reaction method (PCR), which compares the parasites isolated from the blood before and after treatment.

This is done on a set of special genes of the parasite which are polymorphic, meaning they can assume different forms. If all or a majority of parasites had the same composition in these genes it would be impossible to distinguish different parasites - and thus the new from the original infection, said Dr Piero Olliaro, a scientist at TDR who was one of the co-authors of the study.

The study, newly published in the Malaria Journal, analysed these "genetic fingerprints" of parasites and found that these genes are in fact variable enough to distinguish between old and new infections in sub-Saharan Africa (where the vast majority of malaria occurs).

The authors also note, however, that this diversity should be monitored, as malaria is receding in several places (also as a result of better treatment and prevention) and therefore the genetic pool of the malaria parasite may change in the future.

The study was funded by TDR and largely based on material from TDR-funded trials in Malawi, Tanzania, Uganda, Burkina Faso and São Tomé. Additional support was provided by the Swiss Agency for Development and Co-operation (SDC) and the UK Department for International Development (DFID).

For more information, contact: Dr Piero Olliaro