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Competition for hosts modulates vast antigenic diversity to generate persistent strain structure in Plasmodium falciparum.

Abstract：

:In their competition for hosts, parasites with antigens that are novel to the host immune system will be at a competitive advantage. The resulting frequency-dependent selection can structure parasite populations into strains of limited genetic overlap. For the causative agent of malaria, Plasmodium falciparum, the high recombination rates and associated vast diversity of its highly antigenic and multicopy var genes preclude such clear clustering in endemic regions. This undermines the definition of strains as specific, temporally persisting gene variant combinations. We use temporal multilayer networks to analyze the genetic similarity of parasites in both simulated data and in an extensively and longitudinally sampled population in Ghana. When viewed over time, populations are structured into modules (i.e., groups) of parasite genomes whose var gene combinations are more similar within than between the modules and whose persistence is much longer than that of the individual genomes that compose them. Comparison to neutral models that retain parasite population dynamics but lack competition reveals that the selection imposed by host immunity promotes the persistence of these modules. The modular structure is, in turn, associated with a slower acquisition of immunity by individual hosts. Modules thus represent dynamically generated niches in host immune space, which can be interpreted as strains. Negative frequency-dependent selection therefore shapes the organization of the var diversity into parasite genomes, leaving a persistence signature over ecological time scales. Multilayer networks extend the scope of phylodynamics analyses by allowing quantification of temporal genetic structure in organisms that generate variation via recombination or other non-bifurcating processes. A strain structure similar to the one described here should apply to other pathogens with large antigenic spaces that evolve via recombination. For malaria, the temporal modular structure should enable the formulation of tractable epidemiological models that account for parasite antigenic diversity and its influence on intervention outcomes.

journal_name

PLoS Biol

journal_title

PLoS biology

authors

Pilosof S,He Q,Tiedje KE,Ruybal-Pesántez S,Day KP,Pascual M

doi

10.1371/journal.pbio.3000336

subject

Has Abstract

pub_date

2019-06-24 00:00:00

pages

e3000336

issue

eissn

1544-9173

issn

1545-7885

pii

PBIOLOGY-D-18-00584

journal_volume

pub_type

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Competition for hosts modulates vast antigenic diversity to generate persistent strain structure in Plasmodium falciparum.