Little is known about resistance of Plasmodium falciparum to antimalarials in Sahelian countries. Here we investigated the drug susceptibilities of fresh isolates collected in Niger post-deployment of artemisinin-based combination therapies (ACTs). We found that the parasites remained highly susceptible to new (dihydroartemisinin, lumefantrine, pyronaridine, and piperaquine) and conventional (amodiaquine and chloroquine) antimalarial drugs. The introduction of ACTs in 2005 and their further deployment nationwide have therefore not resulted in a decrease in P. falciparum susceptibilities to these antimalarials.
The WHO estimates that 50% of the world's population is exposed to malaria. In 2010, 216 million cases and more than 650,000 deaths from malaria were reported. Despite a decrease in the number of confirmed cases in some parts of the world, the situation remains heterogeneous and worrying in Africa (1). Together with respiratory infections and diarrheal diseases, malaria is one of the leading causes of death in Niger. Malaria transmission rates are high, with a mean incidence of 80 cases per 1,000 inhabitants. Despite the complementary nature of interventions in the field, which have strengthened in recent years, the number of cases has steadily risen over the last 20 years, reaching three million in 2010 (2, 3). There are several reasons for the deterioration of the public health situation with regard to malaria, and the increase in resistance to antimalarial drugs is considered a key factor. In Niger, infections are currently treated with combinations of drugs including an artemisinin (ART) derivative (artemisinin-based combination treatment, or ACT) (4). Since 2005, ACT has been proposed as the first-line treatment for the management of uncomplicated malaria. The use of such treatments throughout Niger was greatly expanded in 2010 by the implementation of a Global Fund Affordable Malaria Facility mechanism (5). Thereby, the drug pressure exerted on Plasmodium falciparum increases the risk of selection of parasites with altered susceptibility to antimalarials. This seems to be inevitable, as demonstrated by recent observations in Asia, which have revealed the presence of parasites less sensitive to artemisinins (6). The risk of emerging resistance to ACT makes it necessary to monitor the susceptibilities of parasites to antimalarial drugs, particularly those used in combination with artemisinin derivatives, on a regular basis and to search for new molecules with antimalarial activity.In this context, a study was carried out in Niger in 2011, at Gaya in the Dosso region, 250 km south of Niamey (3.44°N, 11.9°E), to evaluate the response of P. falciparum isolates to lumefantrine (LUM) and amodiaquine diphosphate (AQ), both of which are widely used in the ACTs distributed in Niger. In addition, responses to alternative molecules, such as pyronaridine (PYD) and piperaquine (PIP), both currently not available in Niger, as well as dihydroartemisinin (DHA) and chloroquine (CQ), were investigated. P. falciparum is...