Eco-evolutionary dynamics of adapting pathogens and host immunity
arxiv(2024)
摘要
As pathogens spread in a population of hosts, immunity is built up and the
pool of susceptible individuals is depleted. This generates selective pressure,
to which many human RNA viruses, such as influenza virus or SARS-CoV-2, respond
with rapid antigenic evolution and frequent emergence of immune evasive
variants. However, the host's immune systems adapt and older immune responses
wane, such that escape variants only enjoy a growth advantage for a limited
time. If variant growth dynamics and reshaping of host-immunity operate on
comparable time scales, viral adaptation is determined by eco-evolutionary
interactions that are not captured by models of rapid evolution in a fixed
environment. Here, we use a Susceptible/Infected model to describe the
interaction between an evolving viral population in a dynamic but
immunologically diverse host population. We show that depending on strain
cross-immunity, heterogeneity of the host population, and durability of immune
responses, escape variants initially grow exponentially, but lose their growth
advantage before reaching high frequencies. Their subsequent dynamics follows
an anomalous random walk determined by future escape variants and results in
variant trajectories that are unpredictable. This model can explain the
apparent contradiction between the clearly adaptive nature of antigenic
evolution and the quasi-neutral dynamics of high frequency variants observed
for influenza viruses.
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