Prevalence and risk factors of Coxiella burnetii seropositivity in Danish beef and dairy cattle at slaughter adjusted for test uncertainty

Abstract

Antibodies to Coxiella burnetii have been found in the Danish dairy cattle population with high levels of herd and within herd seroprevalences. However, the prevalence of antibodies to C. burnetii in Danish beef cattle remains unknown. The objectives of this study were to (1) estimate the prevalence and (2) identify risk factors associated with C. burnetii seropositivity in Danish beef and dairy cattle based on sampling at slaughter. Eight hundred blood samples from slaughtered cattle were collected from six Danish slaughter houses from August to October 2012 following a random sampling procedure. Blood samples were tested by a commercially available C. burnetii antibody ELISA kit. A sample was defined positive if the sample-to-positive ratio was greater than or equal to 40. Animal and herd information were extracted from the Danish Cattle Database. Apparent (AP) and true prevalences (TPs) specific for breed, breed groups, gender and herd type; and breed-specific true prevalences with a random effect of breed was estimated in a Bayesian framework. A Bayesian logistic regression model was used to identify risk factors of C. burnetii seropositivity. Test sensitivity and specificity estimates from a previous study involving Danish dairy cattle were used to generate prior information. The prevalence was significantly higher in dairy breeds (AP=9.11%; TP=9.45%) than in beef breeds (AP=4.32%; TP=3.54%), in females (AP=9.10%; TP=9.40%) than in males (AP=3.62%; TP=2.61%) and in dairy herds (AP=15.10%; TP=16.67%) compared to beef herds (AP=4.54%; TP=3.66%). The Bayesian logistic regression model identified breed group along with age, and number of movements as contributors for C. burnetii seropositivity. The risk of seropositivity increased with age and increasing number of movements between herds. Results indicate that seroprevalence of C. burnetii is lower in cattle sent for slaughter than in Danish dairy cows in production units. A greater proportion of this prevalence is attributed to slaughtered cattle of dairy breeds or cattle raised in dairy herds rather than beef breeds.

Keywords: Bayesian analysis; Cattle; Coxiella burnetii; Seroprevalence; Test uncertainty; True prevalence.