Avoiding extinction by migration: The case of the head louse

TL;DR

This study uses a computational model to demonstrate that migration among hosts can prevent the extinction of head lice populations, highlighting the importance of host group size and contagion probability.

Contribution

It introduces a realistic model showing how migration among hosts sustains head lice populations, extending previous work on population persistence.

Findings

Migration prevents lice extinction in small host groups.

Lice infestation can become endemic depending on host group size and contagion probability.

Small contact networks are sufficient for long-term lice survival.

Abstract

The possibility of spreading by migration, colonizing new spatial domains suitable for development and reproduction, can substantially relieve a biological population from the risk of extinction. By means of a realistic computational model based on empirical data, we study this phenomenon for the human head louse, Pediculus humanus capitis. In particular, we show that a lice colony infesting a single isolated host is prone to extinction by stochastic population fluctuations within an interval of several months, while migration over a relatively small group of hosts in contact with each other is enough to insure the prevalence of the infestation for indefinitely long periods. We characterize the interplay of the size of the host group with the host-to-host contagion probability, which controls a transition between extinction of the lice population and a situation where the infestation is endemic.