Onset and duration of immunity in guinea pigs and mice induced with different Q fever vaccines.

Protective effects of different types of Q fever vaccines, namely untreated Coxiella burnetii phase I cells (Cb I) or Cb I cells treated with chloroform-methanol (CM) mixture (Cb I-CM) and of a Q fever chemovaccine obtained by trichloroacetic acid extraction (TCAE) from intact Cb I cells, were compared in mice and guinea pigs at different intervals after intraperitoneal (i.p.) or subcutaneous (s.c.) immunizations. The highest degree of protection at all intervals studied was achieved with Cb I cells, irrespective of the route of immunization and i.p. or aerosol challenge. This vaccine exerted a protective effect in guinea pigs and mice as early as after one or two weeks post-immunization, the effect lasting for at least 40 weeks in mice (i.p. challenge) and 12 months in guinea pigs (aerosol challenge). Addition of small amount of Cb I cells to TCAE increased resistance of guinea pigs to aerosol challenge. Degree, onset and duration of protection to either type of virulent challenge afforded by Cb I-CM cells and TCAE was similar, but when compared with that of Cb I cells it was lower, started later (from the 2nd week in guinea pigs and the 3rd week in mice), and in mice it lasted for a shorter period (20 weeks only). The resistance to virulent challenge in guinea pigs did not depend on the levels of microagglutination (MA) antibodies and in mice it was reflected by delayed type hypersensitivity (DTH) reaction and adoptively transferred splenocytes, rather than by MA antibody titres and passive transfer of immune sera to recipient mice.(ABSTRACT TRUNCATED AT 250 WORDS)