Surveillance of Coxiella burnetii Shedding in Three Naturally Infected Dairy Goat Herds after Vaccination, Focusing on Bulk Tank Milk and Dust Swabs

Abstract

Q fever outbreaks on three dairy goat farms (A-C) were monitored after the animals had been vaccinated with an inactivated Coxiella burnetii phase I vaccine. The antibody response was measured before vaccination by serum samples with two C. burnetii phase-specific ELISAs to characterize the disease status. Shedding was determined by vaginal swabs during three kidding seasons and monthly bulk tank milk (BTM) samples. Dust swabs from one windowsill of each barn and from the milking parlors were collected monthly to evaluate the indoor exposure. These samples were analyzed by qPCR. The phase-specific serology revealed an acute Q fever infection in herd A, whereas herds B and C had an ongoing and past infection, respectively. In all three herds, vaginal shedders were present during three kidding seasons. In total, 50%, 69%, and 15% of all collected BTM samples were C. burnetii positive in herds A, B, and C, respectively. Barn dust contained C. burnetii DNA in 71%, 45%, and 50% of examined swabs collected from farms A, B, and C, respectively. The largest number of C. burnetii positive samples was obtained from the milking parlor (A: 91%, B: 72%, C: 73%), indicating a high risk for humans to acquire Q fever during milking activity.

Keywords: One Health; Q fever; bulk tank milk; dust swab; goat; longitudinal study; milking parlor; phase-specific serology; vaccination; zoonosis.

Figure 1

Median levels of IgG phase I and phase II Coxiella burnetii antibodies in three naturally infected dairy goat herds (A–C) at the start of the investigation in 2018. * p < 0.05; c/o = ELISA cut-off.

Figure 2

Coxiella burnetii shedding through vaginal route during three (2018–2020) kidding seasons (K-season) in three naturally C. burnetii infected dairy goat herds (A–C) analyzed by qPCR. All goat herds were vaccinated after C. burnetii had been diagnosed in 2018.

Figure 3

Coxiella burnetii detection by qPCR (Cq ≤ 45: positive result) in monthly collected bulk tank milk specimens ◆ and dust samples from one windowsill of each barn ✖ and from each milking parlor ● in three naturally C. burnetii infected and vaccinated dairy goat herds (A–C). BTM samples were not always available at every sampling date from farm A and C. Green bar: kidding period; syringe: vaccination; missing samples are not indicated.