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Clin Infect Dis. 2013 Jul;57(1):40-7. doi: 10.1093/cid/cit174. Epub 2013 Mar 13.

An intensive longitudinal cohort study of Malian children and adults reveals no evidence of acquired immunity to Plasmodium falciparum infection.

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1
Laboratory of Immunogenetics, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Rockville, MD 20852, USA.

Abstract

BACKGROUND:

In experimental models of human and mouse malaria, sterilizing liver stage immunity that blocks progression of Plasmodium infection to the symptomatic blood stage can be readily demonstrated. However, it remains unclear whether individuals in malaria-endemic areas acquire such immunity.

METHODS:

In Mali, 251 healthy children and adults aged 4-25 years who were free of blood-stage Plasmodium infection by polymerase chain reaction (PCR) were enrolled in a longitudinal study just prior to an intense 6-month malaria season. Subsequent clinical malaria episodes were detected by weekly active surveillance and self-referral. Asymptomatic P. falciparum infections were detected by blood-smear microscopy and PCR analysis of dried blood spots that had been collected every 2 weeks for 7 months.

RESULTS:

As expected, the risk of clinical malaria decreased with increasing age (log-rank test, P = .0038). However, analysis of PCR data showed no age-related differences in P. falciparum infection risk (log-rank test, P = .37).

CONCLUSIONS:

Despite years of exposure to intense P. falciparum transmission, there is no evidence of acquired, sterile immunity to P. falciparum infection in this population, even as clinical immunity to blood-stage malaria is clearly acquired. Understanding why repeated P. falciparum infections do not induce sterile protection may lead to insights for developing vaccines that target the liver stage in malaria-endemic populations.

KEYWORDS:

Plasmodium falciparum; endemic population; infection risk; malaria; preerythrocytic immunity

PMID:
23487390
PMCID:
PMC3669526
DOI:
10.1093/cid/cit174
[Indexed for MEDLINE]
Free PMC Article
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