Subclinical effects of Coxiella burnetii in dairy cows in the Netherlands

Abstract

Coxiella burnetii (Cb) is an obligate intracellular bacterium which causes Q fever in humans and animals. The majority of Dutch dairy herds are considered infected based on bulk milk tank tests for antibody and Cb DNA. Commonly, infected cattle are without any clinical symptoms. However subclinical effects on fertility and udder health have been reported to be associated with Cb prevalence. The aim of this study is to investigate the presence of Cb in the genital tract and the udder in a random sample of 349 healthy slaughter cattle in the Netherlands and the possible relation with suboptimal fertility and mastitis. Therefore, different immunodiagnostic tests are used, such as Cb specific antibody detection, and Cb antigen specific interferon-gamma (IFN-gamma) release and related to the presence of bacterial DNA. In Dutch dairy cattle a high animal level prevalence of Cb infection was observed based on serological diagnostic assays. Surprisingly, an even higher fraction of animals had antibodies against Cb in the milk. Using qPCR to detect Cb DNA, we were unable to detect Cb in genital tract tissue. However, Cb DNA could be readily detected in 15% of the milk samples. Whether Cb is indeed a causal agent in reproductive disorders of cattle is unclear. It is abundantly present in the udder, however no association was found between the presence of Cb and IMI. Also, we were unable to demonstrate a relation between (sub)clinical mastitis and the presence of the Cb in the udder or milk . Following from the results more research is needed to elucidate the clinical consequences of an infection with Cb in dairy cattle.