Novel pfdhps haplotypes among imported cases of Plasmodium falciparum malaria in the United Kingdom

Abstract

Treatment of acute malaria caused by Plasmodium falciparum may include long-half-life drugs, such as the antifolate combination sulfadoxine-pyrimethamine (SP), to provide posttreatment chemoprophylaxis against parasite recrudescence or delayed emergence from the liver. An unusual case of P. falciparum recrudescence in a returned British traveler who received such a regimen, as well as a series of 44 parasite isolates from the same hospital, was analyzed by PCR and direct DNA sequencing for the presence of markers of parasite resistance to chloroquine and antifolates. The index patient harbored a mixture of wild-type and resistant pfdhfr and pfdhps alleles upon initial presentation. During his second malaria episode, he harbored only resistant parasites, with the haplotypes IRNI (codons 51, 59, 108, and 164) and SGEAA (codons 436, 437, 540, 581, and 613) at these two loci, respectively. Analysis of isolates from 44 other patients showed that the pfdhfr haplotype IRNI was common (found in 81% of cases). The SGEAA haplotype of pfdhps was uncommon (found only in eight cases of East African origin [17%]). A previously undescribed mutation, I431V, was observed for seven cases of Nigerian origin, occurring as one of two haplotypes, VAGKGS or VAGKAA. The presence of this mutation was also confirmed in isolates of Nigerian origin from the United Kingdom Malaria Reference Laboratory. The presence of the pfdhps haplotype SGEAA in P. falciparum parasites of East African origin appears to compromise the efficacy of treatment regimens that include SP as a means to prevent recrudescence. Parasites with novel pfdhps haplotypes are circulating in West Africa. The response of these parasites to chemotherapy needs to be evaluated.

FIG. 1.

Quantitative PCR analysis of two sequential P. falciparum malaria episodes for the same patient. Episode 1 was treated with quinine; episode 2, with AP. Each point represents the mean estimate of parasite density from two replicates in a single experiment. The y axis shows parasite density, expressed in kilo-international units of P. falciparum DNA, on a logarithmic scale. The x axis shows the approximate time (in hours) after the first diagnostic blood sample was taken. Where the exact time was not recorded, an interval of 24 h between consecutive samples is assumed.

FIG. 2.

Alignment of deduced PfDHPS amino acid sequences from 46 P. falciparum isolates. The eight different PfDHPS haplotypes encoded by DNA sequences determined in this study from patients at the HTD in 2006 are shown, and the number of isolates with each haplotype is given on the left (#). Haplotypes are arranged in increasing order of amino acid substitutions, and substitutions relative to the wild-type sequence are shaded. Amino acids 445 to 530 were invariant and are omitted for clarity. Amino acids 1 to 424 were not sequenced, because there are no previous reports of amino acid substitutions in this region of the polypeptide. Where mixed infections were present, only the dominant haplotype is shown and contributes to the number of isolates given. The novel genotypes VAGKAA and VAGKGS are shown in boldface.