The vectorial capacity of human lice: Pediculus humanus and Pthirus pubis

Abstract

Summary:The body louse (Pediculus humanus humanus) is the vector of Rickettsia prowazekii, the agent of epidemic typhus, Borrelia recurrentis, the agent of louse-borne relapsing fever and Bartonella quintana, and the agent of trench fever. Although Acinobacter baumannii and Serratia marcescens have been detected in body lice, their vectorial capacity for these pathogens is not yet clear. Under experimental conditions, it was shown that body lice become infested and later transmit pathogens such as Yersinia pestis, Rickettsia typhi, Rickettsia conorii and Rickettsia rickettsiae, however in these cases it is not known if this could happen under natural conditions. The vectorial ability of head lice remains quite controversial. Under experimental conditions head lice were infected with R. prowazekii and disseminate this pathogen in their feces, showing that these lice have the potential to be a vector pathogen under optimal epidemiologic conditions, e.g., during outbreaks of epidemic typhus. Head lice and their eggs collected from children and homeless people were tested positive for B. quintana. Pubic lice are not known to be vectors of any human pathogenic microorganisms under field conditions. Human lice are hematophagous ectoparasitic insects. They are permanent parasites specific to humans, spending their entire life on their host. Humans are parasitized by two species of lice: The human louse, Pediculus humanus, which appears in two ecotypes, the head louse, Pediculus humanus capitis and the body louse, Pediculus humanus humanus. The second species is the pubic louse, Pthirus pubis. Infestation with lice can cause dermatitis and pruritus and as a result of scratching, excoriations and secondary infections may develop. Since the early years of the 20 th century, it has been known that body lice are vectors of three pathogenic bacteria: a) Rickettsia prowazekii, the agent of epidemic typhus; b) Borrelia recurrentis, the agent of louse-borne relapsing fever; and c) Bartonella quintana, the agent of trench fever.