Head Louse - Possible Mutualism Between Humans and Headlice

Possible Mutualism Between Humans and Headlice

It was recently suggested that headlice might have been mutualist partners to humans throughout a long period of human evolutionary past up to recent times. The authors argue that childhood headlice infestations may provoke an immune response that provides some defense against body lice infestations later on. This would be beneficial for humans because body lice serve as vectors of lethal human diseases while head lice do not play any vector role. Indeed, body lice are important vectors of epidemic or louse-borne typhus, trench fever, louse-borne relapsing fever, and probably even classical bubonic plague. Thus a childhood headlice infestation may serve as a "natural vaccine" against the body lice and the lethal pathogens they may carry. In modern days, however, head lice infestations do not yield any adaptive benefits for the people living in developed countries where the threat exposed by the virulent forms of body-louse-borne diseases is mostly (though not totally) eradicated.