No abstract

Background: In order to maximize the useful therapeutic life of antimalarial drugs, it is crucial to understand the mechanisms by which parasites resistant to antimalarial drugs are selected and spread in natural populations. Recent work has demonstrated that pyrimethamine-resistance conferring mutations in Plasmodium falciparum dihydrofolate reductase (dhfr) have arisen rarely de novo, but spread widely in Asia and Africa. The origin and spread of mutations in Plasmodium vivax dhfr were assessed by constructing haplotypes based on sequencing dhfr and its flanking regions.

We investigated the association between the Plasmodium vivax dihydrofolate reductase (Pvdhfrtas) and the P. vivax dihydropteroate synthase (Pvdhps) genotype and in vitro sensitivity to the antifolates pyrimethamine, WR99210, chlorcycloguanil, sulfadoxine, and dapsone. Drug responses of 32 P. vivax isolates were assessed in two in vitro systems: schizont maturation inhibition and a yeast expression system. The geometric mean of 50% inhibition concentration (IC(50)) values for pyrimethamine, chlorcycloguanil, WR99210, sulfadoxine, and dapsone were 85 +/- 88, 784 +/- 662, 95 +/- 87, 2,424 +/- 2,784, and 1,625 +/- 1,801 nM, respectively, for the schizont maturation assay. Five different Pvdhfr alleles and four Pvdhps alleles were observed: 26 of 32 quadruple mutant alleles of Pvdhfr (F57I,L/S58R/T61M/S117T), four triple mutants (S58R/T61M/S117T, K49C/S58R/S117N), and two double mutant isolates (S58R/S117N). All isolates carried Pvdhps 585V. Twenty four isolates carried double mutant Pvdhps (A383G/A553G), six an additional mutation, S382A,C/A383G/A553G, and two a single mutation, A383G. Increasing geometric mean IC(50) values were observed with increased number of Pvdhfr mutations from double to quadruple. Results suggest that quadruple mutant alleles confer decreased sensitivity to pyrimethamine but retain sensitivity to WR99210.

Legionnaires' disease (LD) can be fatal among high-risk transplant recipients. To understand the epidemiology of LD, we reviewed 15-year longitudinal data from a center in Seattle, Washington that cares for both solid organ transplant (SOT) and hematopoietic cell transplant (HCT) recipients. We identified all laboratory-confirmed LD and extracted data on species, diagnostic modalities, clinical presentation, management, and outcomes from medical records. Among 32 patients with LD, transplant recipients made up the majority of diagnoses (22, 69%; SOT 10, HCT 12). Approximately 0.8% of transplant recipients who underwent Legionella-specific testing were positive. Non-pneumophila Legionella species (LNLP), which are not detected by urinary antigen test, accounted for half the cases, led by Legionella micdadei (32%). The severity and outcome between Legionella pneumophila and LNLP infections were similar (attributed mortality, 36% vs 27%); all LNLP deaths occurred in transplant recipients with L. micdadei. The clinical and radiological features mimicked other opportunistic pathogens; 32% (n=7) were not on empiric treatment at the time of diagnosis. These data add to the emerging literature describing the importance of LD and highlight the need for both routine Legionella testing on transplant recipients with pulmonary findings and empiric Legionella-active antibiotic therapy.