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BACKGROUND: Plasmodium falciparum reticulocyte-binding protein homologue 5 (PfRH5) is a blood-stage parasite protein essential for host erythrocyte invasion. PfRH5-specific antibodies raised in animals inhibit parasite growth in vitro, but the relevance of naturally acquired PfRH5-specific antibodies in humans is unclear. METHODS: We assessed pre-malaria season PfRH5-specific immunoglobulin G (IgG) levels in 357 Malian children and adults who were uninfected with Plasmodium. Subsequent P. falciparum infections were detected by polymerase chain reaction every 2 weeks and malaria episodes by weekly physical examination and self-referral for 7 months. The primary outcome was time between the first P. falciparum infection and the first febrile malaria episode. PfRH5-specific IgG was assayed for parasite growth-inhibitory activity. RESULTS: The presence of PfRH5-specific IgG at enrollment was associated with a longer time between the first blood-stage infection and the first malaria episode (PfRH5-seropositive median: 71 days, PfRH5-seronegative median: 18 days; P = .001). This association remained significant after adjustment for age and other factors associated with malaria risk/exposure (hazard ratio, .62; P = .02). Concentrated PfRH5-specific IgG purified from Malians inhibited P. falciparum growth in vitro. CONCLUSIONS: Naturally acquired PfRH5-specific IgG inhibits parasite growth in vitro and predicts protection from malaria. These findings strongly support efforts to develop PfRH5 as an urgently needed blood-stage malaria vaccine. CLINICAL TRIALS REGISTRATION: NCT01322581.

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.

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Introduction: The objective of our study was to establish the epidemiological profile of COVID-19 in Tombouctou., Material and Methods: This was a descriptive cross-sectional study of COVID-19 surveillance data from Tombouctou from April 3 to October 1, 2020. Our variables of interest were extracted from the surveillance database and analyzed with Excel 2013. The frequencies, rate, and ratio were computed., Results: Overall, 1851 suspects from all districts of the region were screened by RT-PCR, including 572 confirmed, which indicate a positivity rate of 30.90%. The 15-34 age group was the most represented with 48% of the confirmed cases. The sex ratio (male / female) of confirmed cases was 2.67. The city of Tombouctou was the epicenter of COVID-19. The Tombouctou region had a detection rate of around 2‰ (1851/928,000) and peaked between weeks 22 and 23 with a case fatality of 2.8%., Conclusion: Young people and men were most likely to be infected with COVID-19. We recommend increasing awareness of compliance with barrier measures., (Le comité de rédaction se réserve le droit de renvoyer aux auteurs avant toute soumission à l'avis des lecteurs les manuscrits qui ne seraient pas conformes à ces modalités de présentation. En outre il leur conseille de conserver un exemplaire du manuscrit, des figures et des tableaux.)