COXIELLA BURNETI IN A WILDLIFE-LIVESTOCK ENVIRONMENT

Enright J. B. (Dept. of Epidemiology and Preventive Medicine, Univ. of California, Davis, Calif. 95616), C. E. Franti, W. M. Longhurst, D. E. Behymer, M. E. Wright and V. J. Dutson. Coxiella burnefi in a wildlife-livestock environment; antibody response of ewes and lambs in an endemic Q fever area. Amer J Epidem 94: 62–71, 1971.—Two independent cycles of Q fever have been hypothesized: one in wildlife and the other in domestic livestock. We investigated the prevalence of Q fever antibodies in livestock and wildlife sharing the same habitat to determine the ecology of Coxiella burneti under the influence of these two cycles. A serological study of ewes and lambs during a 2-year period indicated a recurring annual cycle of Q fever in sheep. Seasonal changes in the prevalence of phase II complement-fixing (CF) antibodies to C. burneti in sheep are believed to reflect their exposure to the rickettsiae. The peak prevalence of CF antibodies in ewes (55%) was in March, 8 to 12 weeks following the December-February lambing period. This peak may be in response to exposure to C. burneti shed during parturition. The prevalence of CF antibodies in ewes was lowest in late September (18%). Lambs born in two consecutive years were tested at birth and on selected dates through their first year of life. The levels of detectable Q fever CF antibodies were similar in these two populations: from 7 to 18% of the lambs were antibody positive on the day of birth and the prevalence of CF antibodies in lambs slowly increased through the summer to a peak of approximately 30% in September. The level of antibodies in these cohorts declined through the fall but reflected an increase in the prevalence of detectable antibodies during the respective succeeding lambing periods. By the end of the first year the prevalence of phase II complement-fixing antibodies to C. burneti in lambs was similar to that in adult sheep in the population. The major source of infection in the sheep popution appears to be C. burneti shed in the placentas of infected ewes during the lambing season. There was no evidence that the prevalence of Q fever in these sheep was influenced by wildlife.