Spread of Q fever within dairy cattle herds: key parameters inferred using a Bayesian approach

Abstract

Q fever is a worldwide zoonosis caused by Coxiella burnetii. Although ruminants are recognized as the most important source of human infection, no previous studies have focused on assessing the characteristics of the bacterial spread within a cattle herd and no epidemic model has been proposed in this context. We assess the key epidemiological parameters from field data in a Bayesian framework that takes into account the available knowledge, missing data and the uncertainty of the observation process owing to the imperfection of diagnostic tests. We propose an original individual-based Markovian model in discrete time describing the evolution of the infection for each animal. Markov chain Monte Carlo methodology is used to estimate parameters of interest from data consisting of individual health states of 217 cows of five chronically infected dairy herds sampled every week for a four-week period. Outputs are the posterior distributions of the probabilities of transition between health states and of the environmental bacterial load. Our findings show that some herds are characterized by a very low infection risk while others have a mild infection risk and a non-negligible intermittent shedding probability. Moreover, the antibody status seems to be a key point in the bacterial spread (shedders with antibodies shed for a longer period of time than shedders without antibodies). In addition to the biological insights, these estimates also provide information for calibrating simulation models to assess control strategies for C. burnetii infection.

Serological and shedding patterns after Coxiella burnetii vaccination in the third gestation trimester in dairy cows

“…According to other authors, C. burnetii seropositivity is a risk factor for bacterial shedding (Courcoul et al, 2010). Moreover, consistent with our findings, seroconversion is not observed in non-vaccinated animals (Böttcher et al, 2011;Nogareda et al, 2012) reflecting the high stability of C. burnetii antibodies.…”

“…This validated test (García-Pérez et al, 2009) was performed according to the manufacturer's instructions. The sensitivity and specificity of ELISA are 85% and 95%, respectively (Courcoul et al, 2010). The antigen for the ELISA CoxLS kit was isolated from domestic ruminants by INRA in Nouzilly (France).…”

Dairy goat demography and Q fever infection dynamics

“…Table with definitions of the epidemiological model parameters and their values used for simulations [13,24,25]. …”

Coxiella burnetii antibody dynamics in heifers born to vaccinated versus non-vaccinated dams in a chronically infected dairy herd

“…In contrast, several studies have identified parity (McCaughey et al, 2010;Böttcher et al, 2011;Paul et al, 2012;Tutusaus et al, 2013), C. burnetii shedding (Guatteo et al, 2007;Courcoul et al, 2010) and vaccination against the bacterium as maternal factors related to the C. burnetii seropositivity of their offspring. The lack of effects of these factors observed here may be explained by our small sample size.…”

“…A sample was scored positive when the S/P ratio > 0.4. The sensitivity and specificity of this ELISA test have been estimated to be 85% and 95%, respectively (Courcoul et al, 2010).…”