Immunization against Q-fever of naturally infected dairy cows.

Dairy cows infected naturally with Coxiella burnetii as evidenced either by presence of phase II agglutinating antibodies in the blood or by shedding C. burnetii in the milk, were vaccinated subcutaneously with formalin-killed phase I C. burnetii organisms. Attempts to demonstrate C. burnetii in the milk of vaccinated dairy cows 47 days after vaccination were negative, while continuous shedding of C. burnetii in the milk of control non-vaccinated dairy cows was repeatedly demonstrated in the course of 123 days (period of investigation). No harmful systemic reaction following vaccination was observed.