Biological Relationships Between Lice (Anoplura) and Microbial Agents

Abstract

Normally the bodies of sucking lice (Anoplura) are free from pathogenic microorganisms. Sterility of the intestinal contents is one of the important factors determining the optimal conditions for life of lice, which can even rid themselves of microbial agents-at least to a certain degree. Symbiotes are the only permanent and obligatory residents of the bodies of lice. They furnish nutritive substances which are indispensable for the growth and reproduction of their hosts [Aschner (3); Puchta (61)]. On the other hand, lice are known to be vectors of spirochetes and rickett­ siae; epidemic typhus, trench fever, and relapsing fever are "louse-borne diseases." Not until relapsing fever and certain rickettsial diseases were in­ vestigated, were lice and their role as transmitters of disease agents studied more thoroughly [Buxton (8); Hase (28)]. Today we have a fair knowledge of the relationships between the sucking lice and some of the more important pathogenic agents. We know hardly anything, however, concerning those internal biochemical processes which govern the association of lice and microbial agents. For practical reasons, the main object of investigation has been the body louse, Pediculus humanus humanus Linnaeus. Our knowledge regarding the same relations between animal lice and microbial agents are much more incomplete. While fundamental observations on the role of lice as vectors of diseases were made years ago, recent investigations have broadened our knowledge. Spirochetes and rickettsiae are probably the only true parasites of sucking lice. Hence we will deal mainly with these parasites in this paper; only the more significant observations and experiments that pertain to the behavior of other blood parasites borne by lice, and their transmission, will be re­ ported. Here the relationships between host and parasite are either acci­ dental and short-termed or have not been sufficiently explained as yet. Since many of the observations made are based upon laboratory experiments, the techniques that have been applied have a bearing on the results and must, therefore, be briefly discussed.