Antibody response to Rocky Mountain spotted fever

Immune responses to Rickettsia akari infection in congenitally athymic nude mice

Athymic BALB/c nude mice and euthymic BALB/c mice were infected with Rickettsia akari by the intraperitoneal route. The rickettsialpox infection was terminated in euthymic mice with only two intraperitoneal injections of the antibiotic oxytetracycline, whereas prolonged treatment was necessary to terminate the infection in athymic mice. Both athymic and euthymic mice produced specific antibody, but athymic mice were still susceptible to reinfection. Killed R. akari served as a protective immunogen in euthymic, but no in athymic, mice. When spleen cells from convalescent euthymic mice were transferred to syngeneic athymic mice, recipients showed protection against challenge. This suggests that a T-cell-dependent step is generally necessary to terminate the rickettsialpox infection.

Suppression of cellular immune responses in guinea pigs infected with spotted fever group rickettsiae

Using a guinea pig model, we demonstrated that infections with pathogenic species of spotted fever group rickettsiae transiently and nonspecifically suppress established cellular immune responses as measured by in vitro lymphocyte transformation and in vivo delayed cutaneous hypersensitivity responses to unrelated, nonrickettsial antigens. The correlation of the duration of this immunosuppression with the virulence of the infecting rickettsial species suggests that this suppression is a pathological effect of the rickettsial infection. Although we did not specifically study the mechanism of this suppression, it is not associated with either lymphocytopenia or leukocytosis.

Laboratory-acquired Rocky Mountain spotted fever. The hazard of aerosol transmission

Nine patients with laboratory-acquired Rocky Mountain spotted fever were seen during the period 1971 to 1976. Investigation of each case revealed either definite or probable exposure to an aerosol containing infectious rickettsiae; in no case was there evidence of parenteral exposure either by accidental self-inoculation or by tick bite. These illnesses are believed to represent infection acquired via the respiratory route. This report emphasizes the aerosol hazard of Rickettsia rickettsii in the laboratory and discusses the possibility of respiratory transmission of Rocky Mountain spotted fever in nature. The illness occurred only in personnel who had received either no vaccination or the primary series of the commercial (Lederie) vaccine against this infection. Other personnel who had received the primary series with multiple booster vaccinations demonstrated increased immunity as measured by humoral antibody titers and rickettsial antigen-induced lymphocyte transformation; no cases of clinical disease developed in these multiply-vaccinated personnel.

Effect of vaccination schedule on immune response of Macaca mulatta to cell culture-grown Rocky Mountain spotted fever vaccine

The effect of vaccination schedule on the immune response of Macaca mulatta to formalin-inactivated chicken embryo cell culture (CEC)-grown Rickettsia rickettsii vaccine was studied. Schedules consisted of inoculation on day 1 only, on days 1 and 15, on days 1 and 30, on days 1, 8, and 15, or on days 1, 15, and 45. Humoral antibody measured by microagglutination and indirect immunofluorescence and resistance to challenge with 10(4) plaque-forming units of yolk sac-grown R. rickettsii were assessed. Seroconversion was noted in all monkeys after the first dose of vaccine. A second dose administered 8 or 15 days after the primary infection, or a third given 7 or 30 days after the second, produced no long-term effect on antibody titer. Only monkeys given two doses of vaccine at a 30-day interval showed an increase in antibody titer during the period before challenge. Vaccination with one, two, or three doses of CEC vaccine prevented development of rash and rickettsemia after challenge. The two-dose schedules appeared to induce the highest degree of resistance to challenge, as indicated by unaltered hematological parameters and body temperature in monkeys. The one- and three-dose schedules were somewhat less effective, in that some challenged monkeys within each group displayed febrile and leukocyte responses associated with Rocky Mountain spotted fever infection. Our data suggest that administration of two doses of CEC vaccine at 15- or 30-day intervals is the immunization schedule of choice.