Citation Information: JCI Insight. 2021. https://doi.org/10.1172/jci.insight.146443.
Abstract
BACKGROUND. Naturally acquired immunity to malaria is incompletely understood. We used controlled human malaria infection (CHMI) to study the impact of past exposure to malaria in Kenyan adults in relation to infection with a non-Kenyan parasite strain. METHODS. We administered 3.2x103 aseptic, purified, cryopreserved Plasmodium falciparum (Pf) sporozoites (SPZ) [Sanaria® PfSPZ Challenge, NF54 West African strain] by direct venous inoculation and undertook clinical monitoring and serial quantitative PCR (qPCR) of the 18S ribosomal RNA gene. The study endpoint was met when either: parasitaemia reached ≥500 parasites/μl blood; clinically significant symptoms were seen; or at 21 days after inoculation. All volunteers received antimalarial drug treatment on meeting the endpoint. RESULTS. One hundred and sixty-one (161) volunteers underwent CHMI between Aug 4, 2016, and Feb 14, 2018. CHMI was well tolerated with no severe or serious adverse events. Nineteen volunteers (11.8%) were excluded from the analysis based on detection of antimalarial drugs above the minimal inhibitory concentration or parasites genotyped as non-NF54. Of the 142 volunteers who were eligible for analysis: 26 (18.3%) had febrile symptoms and were treated; 30 (21.1%) reached ≥500 parasites/μl and were treated; 53 (37.3%) had parasitaemia without meeting thresholds for treatment and; 33 (23.2%) remained qPCR negative. CONCLUSION. We find that past exposure to malaria, as evidenced by location of residence, in some Kenyan adults can completely suppress in vivo growth of a parasite strain originating from outside Kenya. TRAIL REGISTRATION. The study was registered on ClinicalTrials.gov (NCT02739763). FUNDING. Wellcome Trust
Authors
Melissa C. Kapulu, Patricia Njuguna, Mainga Hamaluba, Domtila Kimani, Joyce M. Ngoi, Janet Musembi, Omar Ngoto, Edward Otieno, Peter F. Billingsley
