A Survey of Q Fever (Coxiella burnetii) in California Dairy Cows

SUMMARY Dairy cattle from 20 dairies in 17 counties throughout California were tested for evidence of infection with Coxiella burnetii , the causative agent of Q fever in man. Of 1,052 dairy cows tested, 82% had agglutinating antibodies to the rickettsia in their serum. Geographically, 92% of 380 dairy cows in south-ern California and 77% of cows in northern California were seropositive. Of 1,634 dairy cows, 51% had specific agglutinating antibodies in their whey, and 23% of 840 cows were found to be shedding C burnetii in their milk. The highest rate (62%) of cows shedding the organism in their milk was among 150 cows tested on densely populated dairies in south-ern California, and the lowest rate of shedding (12%) was found in the dairies on the central coast. In California's Central Valley, 15% of 127 cows in the south-ern part and 17% of 367 cows in the northern part were shedding rickettsiae in their milk. Of 1,473 calves and heifers tested, 34% had antibodies to C burnetii . The antibody prevalence increased with the age of the heifers and was highest in the latter half of pregnancy. The highest prevalence of seropositive calves and heifers was associated with dairies having a high prevalence of infected cows, and the lowest prevalence was among calves and heifers on open range or pasture. Present observations reveal a sevenfold increase in serum reactors among California dairy cows compared with the prevalence of reactors found 25 years ago in a survey by the California Department of Public Health.