ANTIBODY AND ANTIBIOTIC ACTION ON RICKETTSIA PROWAZEKI IN BODY LICE ACROSS THE HOST-VECTOR INTERFACE, WITH OBSERVATIONS ON STRAIN VIRULENCE AND RETRIEVAL MECHANISMS

Using a membrane feeding technique to administer known quantities of rickettsiae, antibodies and antibiotics, the influence of a series of variables in the host-vector-agent interaction on the replication of Rickettsia prowazeki in the human body louse was examined. Rickettsial replication and louse death patterns were indistinguishable whether the lice were infected with the virulent Breinl or the attenuated E strain. Ingestion of blood containing clinically attainable levels of doxycycline or rifampin inhibited rickettsial growth in lice and delayed their death from infection. However, 4 days of “treatment” with either antibiotic failed to eradicate the rickettsiae from the lice and, after a delay, peak rickettsial populations equalled those of untreated controls. Antibodies in serum from a person solidly immune to typhus had no influence at any stage on the rickettsial infection in the louse. The rickettsiae excreted by such lice had detectable amounts of immunoglobulins on their surface. Regardless of strain virulence for man, or the presence or absence of antirickettsial antibodies or of prior exposure to antibiotics, the rickettsiae attained a peak population of 1–2 × 108organisms per louse. Some of the conclusions drawn from these studies and bearing on the epidemiology and control of typhus are as follows: 1) Body lice do not appear to discriminate between rickettsial strains of high and low virulence for man and, in nature, might be capable of transmitting strains of low virulence if available in the blood. 2) Effective antibiotic therapy does not eradicate the rickettsiae from infected lice feeding upon treated patients. The prolonged survival of “treated” infected lice increases the opportunity for typhus transmission and enhances the possibility for the selection of antibiotic resistant rickettsiae. The importance, therefore, of effective louse control measures concurrent with antibiotic therapy is emphasized. 3) If rickettsiae are present in sufficient numbers in the blood of immune or partially immune individuals, lice should be able to (a) retrieve them, (b) provide a favorable environment for their massive replication and (c) reintroduce them into the transmission sequence.