Molecular methods routinely used to detect Coxiella burnetii in ticks cross-react with Coxiella-like bacteria

Abstract

Background

Q fever is a widespread zoonotic disease caused by Coxiella burnetii. Ticks may act as vectors, and many epidemiological studies aim to assess C. burnetii prevalence in ticks. Because ticks may also be infected with Coxiella-like bacteria, screening tools that differentiate between C. burnetii and Coxiella-like bacteria are essential.

Methods

In this study, we screened tick specimens from 10 species (Ornithodoros rostratus, O. peruvianus, O. capensis, Ixodes ricinus, Rhipicephalus annulatus, R. decoloratus, R. geigy, O. sonrai, O. occidentalis, and Amblyomma cajennense) known to harbor specific Coxiella-like bacteria, by using quantitative PCR primers usually considered to be specific for C. burnetii and targeting, respectively, the IS1111, icd, scvA, p1, and GroEL/htpB genes.

Results

We found that some Coxiella-like bacteria, belonging to clades A and C, yield positive PCR results when screened with primers initially believed to be C. burnetii-specific.

Conclusions

These results suggest that PCR-based surveys that aim to detect C. burnetii in ticks by using currently available methods must be interpreted with caution if the amplified products cannot be sequenced. Future molecular methods that aim at detecting C. burnetii need to take into account the possibility that cross-reactions may exist with Coxiella-like bacteria.

• Q fever
• tick-borne diseases
• tick endosymbiont
• false positive
• surveillance
• PCR primers

Acknowledgements

We thank Elodie Rousset for reading and providing comments on the manuscript; Aurélien Joulie, Sébastien Masseglia, and Elise Yang for their involvement in the molecular analyses; and Karen McCoy, Christine Chevillon, Abel Biguezoton, Marcelo Labruna, Patrick Durand, and François Renaud for collecting the ticks.