Falciparum malaria from coastal Tanzania and Zanzibar remains highly connected despite effective control efforts on the archipelago

• Published in: Malaria Journal
• Main Authors: Andrew P. Morgan, Nicholas F. Brazeau, Billy Ngasala, Lwidiko E. Mhamilawa, Madeline Denton, Mwinyi Msellem, Ulrika Morris, Dayne L. Filer, Ozkan Aydemir, Jeffrey A. Bailey, Jonathan B. Parr, Andreas Mårtensson, Anders Bjorkman, Jonathan J. Juliano
• Format: Article in Journal/Newspaper
• Language: English
• Published: BMC 2020
• Subjects: Plasmodium; Malaria; Population genetics; Arctic medicine. Tropical medicine; RC955-962; Infectious and parasitic diseases; RC109-216; Arctic
• Online Access: https://doi.org/10.1186/s12936-020-3137-8; https://doaj.org/article/1e5344cd2c76420fbe64bb4094e7bf94

Abstract Background Tanzania’s Zanzibar archipelago has made significant gains in malaria control over the last decade and is a target for malaria elimination. Despite consistent implementation of effective tools since 2002, elimination has not been achieved. Importation of parasites from outside of the archipelago is thought to be an important cause of malaria’s persistence, but this paradigm has not been studied using modern genetic tools. Methods Whole-genome sequencing (WGS) was used to investigate the impact of importation, employing population genetic analyses of Plasmodium falciparum isolates from both the archipelago and mainland Tanzania. Ancestry, levels of genetic diversity and differentiation, patterns of relatedness, and patterns of selection between these two populations were assessed by leveraging recent advances in deconvolution of genomes from polyclonal malaria infections. Results Significant decreases in the effective population sizes were inferred in both populations that coincide with a period of decreasing malaria transmission in Tanzania. Identity by descent analysis showed that parasites in the two populations shared long segments of their genomes, on the order of 5 cM, suggesting shared ancestry within the last 10 generations. Even with limited sampling, two of isolates between the mainland and Zanzibar were identified that are related at the expected level of half-siblings, consistent with recent importation. Conclusions These findings suggest that importation plays an important role for malaria incidence on Zanzibar and demonstrate the value of genomic approaches for identifying corridors of parasite movement to the island.