Increasingly inbred and fragmented populations ofPlasmodium vivaxwith declining transmission

Abstract

Plasmodium vivax populations are more resistant to malaria control strategies than Plasmodium falciparum, maintaining high genetic diversity and gene flow even at low transmission. To quantify the impact of declining transmission on P. vivax populations, we investigated population genetic structure over time during intensified control efforts and over a wide range of transmission intensities and spatial scales in the Southwest Pacific. Analysis of 887 P. vivax microsatellite haplotypes (Papua New Guinea, PNG = 443, Solomon Islands = 420, Vanuatu =24) revealed substantial population structure among countries and modestly declining diversity as transmission decreases over space and time. In the Solomon Islands, which has had sustained control efforts for 20 years, significant population structure was observed on different spatial scales down to the sub-village level. Up to 37% of alleles were partitioned between populations and significant multilocus linkage disequilibrium was observed indicating substantial inbreeding. High levels of haplotype relatedness around households and within a range of 300m are consistent with a focal and clustered infections suggesting that restricted local transmission occurs within the range of vector movement and that subsequent focal inbreeding may be a key factor contributing to the observed population structure. We conclude that unique transmission strategies, including relapse allows P. vivax populations to withstand pressure from control efforts for longer than P. falciparum. However sustained control efforts do eventually impact parasite population structure and with further control pressure, populations may eventually fragment into clustered foci that could be targeted for elimination.

Lack of Geospatial Population Structure Yet Significant Linkage Disequilibrium in the Reservoir of Plasmodium falciparum in Bongo District, Ghana

“…Sampling all asymptomatic infections at the compound level may in fact reveal spatial heterogeneities as has been observed in a spatially dense dataset of P. vivax infections from Solomon Islands. 31 Nevertheless, the lack of population structure we observed may be advantageous to maintain beneficial traits such as drug resistance genes. 32 Our cross-sectional survey of this population revealed a large proportion of asymptomatic infections (99.5%; N = 199), consistent with a large parasite reservoir contributing to transmission.…”