Why infest the loved ones - Inherent human behaviour indicates former mutualism with head lice

Lajos Rózsa, Péter Apari

Research output: Contribution to journalReview article

4 Citations (Scopus)

Abstract

Head lice transmit to new hosts when people lean their heads together. Humans frequently touch their heads to express friendship or love, while this behaviour is absent in apes. We hypothesize that this behaviour was adaptive because it enabled people to acquire head lice infestations as early as possible to provoke an immune response effective against both head lice and body lice throughout the subsequent periods of their life. This cross-immunity could provide some defence against the body-louse-borne lethal diseases like epidemic typhus, trench fever, relapsing fever and the classical plague. Thus the human 'touching heads' behaviour probably acts as an inherent and unconscious 'vaccination' against body lice to reduce the threat exposed by the pathogens they may transmit. Recently, the eradication of body-louse-borne diseases rendered the transmission of head lice a maladaptive, though still widespread, behaviour in developed societies.

Original languageEnglish
Pages (from-to)696-700
Number of pages5
JournalParasitology
Volume139
Issue number6
DOIs
Publication statusPublished - May 1 2012

Keywords

  • body lice
  • facultative mutualism
  • head lice
  • human behaviour
  • louse-borne diseases

ASJC Scopus subject areas

  • Parasitology
  • Animal Science and Zoology
  • Infectious Diseases

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