Age-dependent acquisition of protective immunity to malaria in riverine populations of the Amazon Basin of Brazil.
Five community-based cross-sectional surveys of malaria morbidity and associated risk factors in remote riverine populations in northwestern Brazil showed average parasite rates of 4.2% (thick-smear microscopy) and 14.4% (polymerase chain reaction [PCR]) in the overall population, with a spleen rate of 13.9% among children 2-9 years of age. Plasmodium vivax was 2.8 times more prevalent than P. falciparum, with rare instances of P. malariae and mixed-species infections confirmed by PCR; 9.6% of asymptomatic subjects had parasitemias detected by PCR. Low-grade parasitemia detected by PCR only was a risk factor for anemia, after controlling for age and other covariates. Although clinical and subclinical infections occurred in all age groups, the risk of infection and disease decreased significantly with increasing age, after adjustment for several covariates in multilevel logistic regression models. These findings suggest that the continuous exposure to hypo- or mesoendemic malaria may induce significant anti-parasite and anti-disease immunity in native Amazonians.
Ladeia-Andrade
Simone
S
Department of Tropical Medicine, Oswaldo Cruz Institute, Rio de Janeiro, Brazil. shawam@uol.com.br
Ferreira
Marcelo Urbano
MU
de Carvalho
Maria Esther
ME
Curado
Izilda
I
Coura
José Rodrigues
JR
D000293:Adolescent; D000328:Adult; D017677:Age Distribution; D001938:Brazil / Q000453:epidemiology; D002648:Child; D002675:Child, Preschool; D003430:Cross-Sectional Studies; D005260:Female; D006798:Housing; D006801:Humans; D015994:Incidence; D016778:Malaria, Falciparum / Q000453:epidemiology* / Q000276:immunology*; D016780:Malaria, Vivax / Q000453:epidemiology* / Q000276:immunology*; D008297:Male; D016133:Polymerase Chain Reaction; D015995:Prevalence; D012307:Risk Factors; D045483:Rivers; D012424:Rural Population; D055815:Young Adult