Malaria treatment is an essential tool to control Plasmodium falciparum disease in endemic countries. Resistance to currently available drugs is one of his main problems . Several mutations linked to resistance have been described in different genes of P. falciparum genome. These mutations take place spontaneously in the parasite, though pharmacological pressure is one of the most important factors involved in their spread .
Resistance to chloroquine appears nowadays in all regions where P. falciparum is present in Africa . The main determinant of chloroquine resistance is the K76I mutation of the pfcrt gene, which left to in vivo and in vitro resistance . In addition, the N86Y and D1246Y mutations in the pfmdr1 gene, together with the occurrence of mutations in the pfcrt gene, reduce susceptibility to chloroquine .
Use of sulphadoxine-pyrimethamine (SP) began in Africa in the early 1980s and was adopted as first-line treatment for non-severe malaria in many sub-Saharan countries. In the last decade, the high resistance levels reached across the continent have led to a change in treatment policies. SP is currently recommended by the World Health Organization (WHO) for intermittent preventive therapy (IPT) in pregnant woman (IPTp) and infants (IPTi) .
Loss in efficacy of either component of SP brings about a reduction in the efficacy of the combination . Resistance to pyrimethamine is related with single nucleotide polymorphisms (SNPs) at codons A16V, N51I, C59R, S108N/T and I164L of the pfdhfr gene. Although the C50R mutation is usually found in South America, it has recently been described in Africa . The I164L mutation is hardly ever seen in Africa, and its association with resistance in this continent is doubtful . In the dhps gene, five SNPs, namely, S436A/F, A437G, K540E, A581G and A613S/T, have been reported to be linked to P. falciparum resistance to sulphadoxine. An increase in the number of mutations in both, pfdhfr and pfdhps, genes leads to an increase in clinical resistance. In Africa, the pfdhfr triple mutant, 51I-59R-108 N, together with the pfdhps double mutant, 437 G-540E, the so called dhfr/dhps quintuple mutation predicts treatment failure with SP .
Nowadays, artemisinin combination therapy (ACT) is used as a first-line treatment in uncomplicated malaria in African countries with artemether-lumefantrine (AL) and artesunate-amodiaquine (AS/AQ) being the combinations used . The SNPs in the pfcrt and pfmdr1 genes are related with the efficacy of amodiaquine, which is structurally related to chloroquine although in vivo and in vitro data suggest that cross-resistance between both molecules is incomplete . The wild-type alleles of the pfmdr1 gene, N86 and D1246, are linked to a decrease in the in vitro response to lumefantrine and artemisinin . After the introduction of AL, an in vivo association has been established with re-infections by strains with wild-type pfmdr1 alleles and the wild-type pfcrt allele, K76 .
The Hospital Carlos III (Madrid, Spain) is a tropical disease reference centre. Its Tropical Medicine and Paediatrics Departments, attends to immigrants and travellers. SNPs in P. falciparum linked to resistance were analysed in patients proceeding from African countries. Samples were collected over a period of eight years, during a transition phase from high SP coverage to treatment with ACT. This study sought to ascertain the prevalence of anti-malarial drug resistant strains during this period, and measure the impact of pharmacological pressure.