Abstract
The human malaria parasite Plasmodium vivax is more resistant to malaria control strategies than Plasmodium falciparum, and maintains high genetic diversity even when transmission is low. To investigate whether declining P. vivax transmission leads to increasing population structure that would facilitate elimination, we genotyped samples from across the Southwest Pacific region, which experiences an eastward decline in malaria transmission, as well as samples from two time points at one site (Tetere, Solomon Islands) during intensified malaria control. Analysis of 887 P. vivax microsatellite haplotypes from hyperendemic Papua New Guinea (PNG, n = 443), meso-hyperendemic Solomon Islands (n = 420), and hypoendemic Vanuatu (n = 24) revealed increasing population structure and multilocus linkage disequilibrium yet a modest decline in diversity as transmission decreases over space and time. In Solomon Islands, which has had sustained control efforts for 20 years, and Vanuatu, which has experienced sustained low transmission for many years, significant population structure was observed at different spatial scales. We conclude that control efforts will eventually impact P. vivax population structure and with sustained pressure, populations may eventually fragment into a limited number of clustered foci that could be targeted for elimination.
Highlights
The international intensification of malaria control over the last 15 years has reduced the global malaria burden by more than 50% with rapidly declining transmission in many endemic regions [1]
Plasmodium vivax is a major human malaria parasite, common in endemic areas outside sub-Saharan Africa, and more difficult to control than other malaria parasite species
Independent studies are needed to understand how P. vivax populations respond to changing transmission levels, in order to inform malaria control and elimination efforts
Summary
The international intensification of malaria control over the last 15 years has reduced the global malaria burden by more than 50% with rapidly declining transmission in many endemic regions [1]. Plasmodium falciparum and Plasmodium vivax are the major agents of human malaria P. vivax is becoming the main source of malaria infection and disease in co-endemic areas because it is more resilient to control efforts [1,2,3,4,5,6,7,8,9] These shifts in species dominance may result from the fact that P. vivax employs unique transmission strategies including dormant liver-stage infections that relapse months to years after the primary infection [10]. The co-transmission of multiple genetically distinct clones to the vector is central to the generation and maintenance of diversity via sexual recombination [19, 20] As infections decline both within and among hosts, it is expected that effective population size, genetic diversity and gene flow will decrease, eventually leading to inbred, structured populations [21,22,23]. The relationship between P. vivax transmission and population genetic parameters remains poorly understood, and requires systematic investigations with declining transmission and in the context of long-term intensified control
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