Studies of the Falls Creek (Texas) strain of relapsing fever spirochetes: Part I. Epidemiological and ecological studies. Part II. Serological studies of the "ticktorium" strain of Borrelia recurrentis var turicatae

A semi-micro method, for studying the serology of relapsing fever spirochete infections in small animals, has been described. Spirochete immobilization (spirochaeticidal activity) has been established as the best of the various antibody phenomena to utilize in studying the serology of Borrelia recurrentis var turucatae infections in the white rat. There are definite antigenic differences between first attack and first relapse spirochetes. There is evidence, however, that relapse passage, using small amounts (less than 0.01 cc) of blood, may result in the development of certain antigenic strains which were involved in the first attack of the animal from which the passage was made. The antigenic strains of the spirochetes in white rats do not show the alternating tendency (A,B,A,B) previously described for certain louse transmitted strains. Nor is it possible, by the methods used in these experiments, to isolate single ("pure") antigenic varieties of the spirochetes such as those reported for louse transmitted strains. First attacks, after tick-bite inoculation, involve multiple antigenic strains of these spirochetes and these multiple strains are not always homologous in different first attack animals. Relapse and interval passages of the spirochetes from tickbite inoculated animals also give rise to multiple antigenic varieties of the spirochetes in the animals receiving the passage blood. Antigenic variation takes place during onset passage of these spirochetes in white rats. In one case, however, this variation, during twenty onset passages, apparently involved only the loss of some, but not all, of the antigenic varieties involved in the original first attack. No evidence of new antigenic varieties, which had not been involved in the original first attack, appeared during these twenty onset passages