Application of fluorescent in situ hybridisation for demonstration of Coxiella burnetii in placentas from ruminant abortions

A fluorescent in situ hybridisation (FISH) assay targeting 16S ribosomal RNA was developed for detection of the zoonotic bacterium Coxiella burnetii in formalin-fixed, paraffin-embedded tissue, and applied on placentas from ruminant abortions. The applicability of the FISH assay was compared to immunohistochemistry (IHC) using human positive control serum in 12 cases of C burnetii-associated placentitis as well as 7 negative control tissue samples. In all 12 cases the bacterium was detected within trophoblasts as well as free in the placental debris by both FISH and IHC. Extensive and significant infection by C. burnetii was revealed in 10 of the cases, whereas a slighter and focal distribution of the bacterium was observed in two cases. 90 aborted placentas from Danish ruminants were investigated by FISH. C burnetii was detected in one bovine case only, representing the first confirmation of C burnetii in Danish animals. The study shows that FISH targeting 16S ribosomal RNA is a feasible diagnostic tool for detection of C burnetii in tissue samples and fully comparable to IHC.