An Intensive Longitudinal Cohort Study of Malian Children and Adults Reveals No Evidence of Acquired Immunity to Plasmodium falciparum Infection
Clinical Infectious Diseases, 2013•academic.oup.com
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 …
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 …
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.
Oxford University Press