A Study of the Antigenic Structure of M-44 Vaccinal Strain of Rickettsia burnetii. Report III,
ARMY MEDICAL RESEARCH INST OF INFECTIOUS DISEASES FREDERICK MD
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The research demonstrated that strain M-44 of Rickettsia burnetti maintains itself for an extended period in Argas ticks. In A. canestrinii and O. moubata, strain M-44 survived at least 250 days and in A. tholozani at least 490 days periods of actual observation. In all seven experiments, strain M-44 remained in phase II after an extended stay in the host, and did not acquire the antigenic component of phase I. In all of the 94 guinea pigs which received injections of a suspension with A. canestrinii and O. moubata and were studied 30, 100, 150 and 250 days following infection complement-fixing antibodies were formed only for phase II. Antigen from the infected ticks figured in the complement-fixing reaction just as for phase II. In the infected guinea pigs, the infection process proceeded without temperature rise, and did not differ in any respect from experimental rickettsiosis produced with M-44 incubated in vitelline membrane of chicken embryo. Thus, following an extended period of existence in Argas ticks, the M-44 strain of Rickettsia burnetti was found to remain in phase II, while its pathogenicity for guinea pigs did not increase.