Field-based evidence for linkage of mutations associated with chloroquine (pfcrt/pfmdr1) and sulfadoxine-pyrimethamine (pfdhfr/pfdhps) resistance and for the fitness cost of multiple mutations in P. falciparum.

Mutations in the Plasmodium falciparum pfcrt gene on chromosome 7 and possibly mutations in pfmdr1 on chromosome 5 have a role in conferring resistance against chloroquine (CQ), as do mutations of pfdhfr on chromosome 4 and pfdhps on chromosome 8 in terms of resistance against sulfadoxine/pyrimethamine (SP). The additive role of multiple mutations in the development of resistance to each drug suggests a non-random occurrence. In this study, parasite isolates were obtained from 50 patients with uncomplicated P. falciparum malaria from rural Eastern Sudan, an endemic setting with minimal overlap of infection. The parasite isolates were genotyped for detection of 12 alleles in CQ and SP resistance genes. Our main findings were: (1) the frequency of mutant alleles, pfcrt K76T, pfmdr1 N86Y, pfdhfr N51I, pfdhfr S108N, pfdhps K540E and pfdhps A581G were; 0.90, 0.86, 0.84, 0.84, 0.80 and 0.20, respectively. (2) No mutations were detected for the pfdhfr loci A16V, C59R and I164L, and for pfdhps loci S436A, A437G and A613S. (3) There was a statistically significant association between the mutations in: (i) the CQ resistance (CQR) genes, pfcrt T76 and pfmdr1 Y86 (P< or =0.001), (ii) the SP resistance (SPR) genes, pfdhfr I51, pfdhfr N108 and pfdhps E540 (P< or =0.001-0.04) and (iii) the CQ "i" and SP "ii" resistance genes (P=0.001) 4. The fitness cost of multiple mutations was revealed by a significantly reduced parasite density of isolates bearing the mutant alleles (P=0.048). However, the significantly higher gametocyte carriage rate among isolates with resistance mutations (P=0.001) is possibly an evolutionary mechanism for survival of mutant parasites.