Epidemiological investigation of Coxiella burnetii in farms after an outbreak of Q fever in slaughterhouse workers.

Q fever is a worldwide zoonosis caused by the bacterium Coxiella burnetii. In January/2015, a Q fever outbreak occurred among workers at a cattle slaughterhouse in southeastern Brazil. This study investigated if C. burnetii was circulating on farms that sent cattle to the slaughterhouse at the time of the 2015-Q fever outbreak. Blood, milk, vaginal swab and tick samples were collected from livestock on 35 farms surrounding the slaughterhouse. Serological analyses with C. burnetii whole antigens indicated that 68.6 % farms (24/35) had at least one seropositive animal, 76.7 % (23/30) farms had seropositive cattle, 37.5 % (3/8) had seropositive sheep, 16.7 % (5/30) had seropositive horses, and 20.8 % (5/24) had seropositive dogs. The overall seropositivity rates were 18.8 % (96/510) for cattle, 4.1 % (4/97) for sheep, 4.7 % (5/106) for horses, and 12.7 % (8/63) for dogs. Antibody endpoint titers ranged from 64 to 8192 in cattle, and up to 128 in sheep, 256 in horses, and 512 in dogs. Cattle had 1.9 times higher odds of seropositivity compared to other species tested. Pregnant females showed 1.6 times higher odds than non-pregnant ones. Molecular analyses revealed C. burnetii DNA (partial sequences of IS1111 and cap genes) in 0.5 % (1/213) cattle milk samples, and in a Rhipicephalus microplus tick. We conclude that C. burnetii exposure was widespread among livestock in the study region. The highest seropositivity rate in cattle suggests their potential utility as sentinels for monitoring bacterial circulation. C. burnetii DNA was detected in a R. microplus tick in Brazil for the first time.