Abstract
Q fever is a widespread zoonotic disease caused by Coxiella burnetii, a ubiquitous intracellular bacterium infecting humans and a variety of animals. Transmission is primarily but not exclusively airborne, and ticks are usually thought to act as vectors. We argue that, although ticks may readily transmit C. burnetii in experimental systems, they only occasionally transmit the pathogen in the field. Furthermore, we underscore that many Coxiella-like bacteria are widespread in ticks and may have been misidentified as C. burnetii. Our recommendation is to improve the methods currently used to detect and characterize C. burnetii, and we propose that further knowledge of Coxiella-like bacteria will yield new insights into Q fever evolutionary ecology and C. burnetii virulence factors.
Highlights
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Our recommendation is to improve the methods currently used to detect and characterize C. burnetii, and we propose that further knowledge of Coxiella-like bacteria will yield new insights into Q fever evolutionary ecology and C. burnetii virulence factors
In humans, limited data support the occurrence of tickborne C. burnetii transmission, including occasional reports of C. burnetii infections in patients bitten by ticks [33,34,35,36,37], or concomitantly infected with tick-borne pathogens [38,39], or positive for Q fever by serology [40]
Summary
Initial exposure to C. burnetii may result in asymptomatic or mild infection and in acute or chronic disease [4,5]. The clinical diagnosis can be very difficult The reasons for this high clinical polymorphism are largely unknown, even if risk factors of severity (e.g., pregnancy, immunosuppression, preexisting cardiac valvulopathy, vascular grafts, and aneurysms) have been described. Most human cases result from the inhalation of dust particles contaminated by infected livestock or animal products [2,4,89]. An effective vaccine (Q-VAX, CSL Limited, Parkville, Victoria, Australia) may be used in Australia for at-risk professions, its use in endemic areas is difficult because it has significant side effects in persons who have been exposed to C. burnetii, requiring pre-vaccination screening [8]
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