Decreasing efficacy of antimalarial combination therapy in Uganda is explained by decreasing host immunity rather than increasing drug resistance.
BACKGROUND
Improved control efforts are reducing the burden of malaria in Africa but may result in decreased antimalarial immunity.


METHODS
A cohort of 129 children aged 1-10 years in Kampala, Uganda, were treated with amodiaquine plus sulfadoxine-pyrimethamine for 396 episodes of uncomplicated malaria over a 29-month period as part of a longitudinal clinical trial.


RESULTS
The risk of treatment failure increased over the course of the study from 5% to 21% (hazard ratio [HR], 2.4 per year [95% confidence interval {CI}, 1.3-4.3]). Parasite genetic polymorphisms were associated with an increased risk of failure, but their prevalence did not change over time. Three markers of antimalarial immunity were associated with a decreased risk of treatment failure: increased age (HR, 0.5 per 5-year increase [95% CI, 0.2-1.2]), living in an area of higher malaria incidence (HR, 0.26 [95% CI, 0.11-0.64]), and recent asymptomatic parasitemia (HR, 0.06 [95% CI, 0.01-0.36]). In multivariate analysis, adjustment for recent asymptomatic parasitemia, but not parasite polymorphisms, removed the association between calendar time and the risk of treatment failure (HR, 1.5 per year [95% CI, 0.7-3.4]), suggesting that worsening treatment efficacy was best explained by decreasing host immunity.


CONCLUSIONS
Declining immunity in our study population appeared to be the primary factor underlying decreased efficacy of amodiaquine plus sulfadoxine-pyrimethamine. With improved malaria-control efforts, decreasing immunity may unmask resistance to partially efficacious drugs.
Greenhouse
Bryan
B
Department of Medicine, University of California, San Francisco, California, USA. bgreenhouse@medsfgh.ucsf.edu
Slater
Madeline
M
Njama-Meya
Denise
D
Nzarubara
Bridget
B
Maiteki-Sebuguzi
Catherine
C
Clark
Tamara D
TD
Staedke
Sarah G
SG
Kamya
Moses R
MR
Hubbard
Alan
A
Rosenthal
Philip J
PJ
Dorsey
Grant
G
D000655:Amodiaquine / Q000008:administration & dosage / Q000627:therapeutic use*; D000818:Animals; D000962:Antimalarials / Q000627:therapeutic use*; D002648:Child; D002675:Child, Preschool; D004338:Drug Combinations; D004351:Drug Resistance; D004359:Drug Therapy, Combination; D006801:Humans; D007223:Infant; D008137:Longitudinal Studies; D008288:Malaria / Q000188:drug therapy* / Q000276:immunology*; D010961:Plasmodium / Q000187:drug effects / Q000235:genetics; D011739:Pyrimethamine / Q000008:administration & dosage / Q000627:therapeutic use*; D013413:Sulfadoxine / Q000008:administration & dosage / Q000627:therapeutic use*; D017211:Treatment Failure; D014454:Uganda
D000962:Antimalarials; D004338:Drug Combinations; D000655:Amodiaquine; C001205:fanasil, pyrimethamine drug combination; D013413:Sulfadoxine; D011739:Pyrimethamine