Evaluation of Seroprevalence and Periparturient Shedding of Coxiella burnetii in a Dairy Herd in Americana, São Paulo, Brazil

Q fever is a globally distributed zoonosis caused by the obligate intracellular Gram-negative bacterium Coxiella burnetii, a highly infectious pathogen with remarkable environmental persistence. Domestic ruminants are the primary source of human infection through inhalation of contaminated aerosols. Clinical manifestations range from acute febrile illness, hepatitis, and pneumonia to severe persistent focalized complications such as endocarditis, osteomyelitis, and vascular infections. Given the limited data available in Brazil, further investigation into the circulation and shedding of C. burnetii is needed. Here, we describe a prospective cohort study evaluating the association between pre-parturition serological status and periparturient shedding of C. burnetii. For serology, an indirect ELISA (ID Screen® Q fever Indirect Multi-species) was used to detect antibodies in serum samples. Vaginal swabs were collected for DNA extraction and subsequent analysis by real-time PCR (qPCR) using specific primers and a probe targeting the IS1111 gene of C. burnetii. Sixty-five percent (67/103) of the herd was seropositive during the prepartum period, indicating prior exposure to C. burnetii. Among the 42 parturient animals, 29 were seropositive, 10 seronegative, and 1 was not serologically evaluated due to logistical constraints. Of the animals that gave birth within 2 months, 28.6% (12/42) were qPCR-positive, with shedding rates of 24.1% (7/29) and 40% (4/10) for seropositive and seronegative animals, respectively. Notably, some animals exhibited Ct values below 25, indicating high bacterial loads and suggesting increased potential for environmental contamination. Shedding in seronegative animals indicates that serology alone underestimates the risk of C. burnetii dissemination. Active circulation in a dairy herd near Americana’s urban area suggests endemic infection and ongoing zoonotic risk via windborne aerosols. Although limited by single-point sampling and total serology, these findings underscore the need for One Health surveillance to protect workers and neighboring populations at the peri-urban interface.