Evolution of malaria mortality and morbidity after the emergence of chloroquine resistance in Niakhar, Senegal

3 Dec 2009

Paul Chinnock

Source: Malaria Journal (see original article or PDF)

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Citation: Munier A, Diallo A, Marra A, Cot M, Arduin P, Ndiaye O, Mboup BM, Gning B, Chippaux JP (2009). Evolution of malaria mortality and morbidity after the emergence of chloroquine resistance in Niakhar, Senegal. Malar J; 8(1):270. [Epub ahead of print]

For many years chloroquine (CQ) was the mainstay of treatment for malaria but resistance to the drug emerged in the 1980s. Beginning in Southeast Asia, resistant strains of the parasite spread across malaria-endemic regions.

In Senegal, West Africa resistance was first noted in 1992. Like many other countries, Senegal was slow to respond and CQ remained the first-line treatment for malaria, until a change in national antimalarial policy in 2003. An increase in the number of deaths due to malaria was reported from many parts of Africa (including Senegal) during the 1990s and this has largely been attributed to CQ resistance. However, a new study has shown that, as is often the case with malaria, things really aren’t that simple.

The retrospective study was done in a demographic surveillance site in the village of Niakhar. Data on malaria morbidity were obtained from health records in three health care facilities, where diagnosis of malaria was based on clinical signs. Source of data concerning malaria mortality were verbal autopsies performed by trained fieldworkers and examined by physicians who identified the probable cause of death. Over the period 1992–2004, there were a total of 110,093 consultations and malaria was clinically diagnosed in 43,232 patients (39.3%).

Surprisingly, malaria mortality was found to have reached a peak in 1995, in which year malaria-attributable mortality was 3.6%. After this it declined, despite the continuing rise in resistance to the drug used to treat the condition (CQ). A further peak (2.9%) occurred in 2002, and in 2004 there was a fall to 1%.

Using trend analysis, the authors calculate that over the entire 1992–2004 the trend for malaria mortality was downwards. They found that malaria morbidity and mortality followed parallel trends, which were closely associated with rainfall. Their conclusion is that, “...while the impact of chloroquine resistance on malaria mortality is probable, it is certainly not the only cause nor even the predominant cause”.

The data are clinic based and it could be argued that an increased proportion of people with malaria might have presented for treatment during the 1990s due to failure of CQ self-medication. However, the authors state that only minority of patients seen in the clinics had been self-medicating for malaria and CQ was rarely available in local markets. They also express confidence that practices in the clinics regarding the diagnosis and treatment of malaria remained consistent during the period of the study.

This study is from just one surveillance site in one country and we do not know whether similar trends existed elsewhere during the same period. However, it puts the impact of drug resistance into some sort of context. Resistance is an important issue determining the choice of drug for first-line treatment, and every effort should be made to hold back the development of resistance to new drugs as they become available. But there are many other factors, some we know about and some we don’t, which have an impact on case numbers and mortality rates.

2009 Munier et al., licensee BioMed Central Ltd.