Abstract
BackgroundThe bacterium Coxiella burnetii is the etiological agent of Q fever and is mainly transmitted via inhalation of infectious aerosols. DNA of C. burnetii is frequently detected in ticks, but the role of ticks as vectors in the epidemiology of this agent is still controversial. In this study, Ixodes ricinus and Dermacentor marginatus adults as well as I. ricinus nymphs were fed on blood spiked with C. burnetii in order to study the fate of the bacterium within putative tick vectors.MethodsBlood-feeding experiments were performed in vitro in silicone-membrane based feeding units. The uptake, fecal excretion and transstadial transmission of C. burnetii was examined by quantitative real-time PCR as well as cultivation of feces and crushed tick filtrates in L-929 mouse fibroblast cells and cell-free culture medium.ResultsTicks successfully fed in the feeding system with engorgement rates ranging from 29% (D. marginatus) to 64% (I. ricinus adults). Coxiella burnetii DNA was detected in the feces of both tick species during and after feeding on blood containing 105 or 106 genomic equivalents per ml blood (GE/ml), but not when fed on blood containing only 104 GE/ml. Isolation and cultivation demonstrated the infectivity of C. burnetii in shed feces. In 25% of the I. ricinus nymphs feeding on inoculated blood, a transstadial transmission to the adult stage was detected. Females that molted from nymphs fed on inoculated blood excreted C. burnetii of up to 106 genomic equivalents per mg of feces.ConclusionsThese findings show that transstadial transmission of C. burnetii occurs in I. ricinus and confirm that I. ricinus is a potential vector for Q fever. Transmission from both tick species might occur by inhalation of feces containing high amounts of viable C. burnetii rather than via tick bites.
Highlights
The bacterium Coxiella burnetii is the etiological agent of Q fever and is mainly transmitted via inhala‐ tion of infectious aerosols
During the rapid engorgement phase, which occurred after approximately 10 days of in vitro feeding, feces production decreased and the ticks engorged to an average weight of 186.2 ± 61.8 mg
The bacteria contained in the feces were infective as verified by culture in L-929 cells and polymerase chain reaction (PCR) (Cq = 25.39) at day 21 post-inoculation. These results suggest that C. burnetii is transmitted transstadially from I. ricinus nymphs to adults and that infected adults excrete the bacteria with their feces during feeding on a non-infected host
Summary
The bacterium Coxiella burnetii is the etiological agent of Q fever and is mainly transmitted via inhala‐ tion of infectious aerosols. Coxiella burnetii is an obligate intracellular bacterium and distributed worldwide with the exception of New Zealand. It is known as the causal agent of Q fever and affects a wide range of hosts including humans [1, 2]. With the introduction of PCR methods, several studies investigating the prevalence of tick-borne pathogens in Europe showed C. burnetii DNA in over 10% of the examined arthropods [20, 21]. Coxiella-like bacteria were discovered as primarily non-pathogenic tick endosymbionts [27, 28] Their close genetic relationship to C. burnetii could have led to misidentifications by PCR [29, 30]. These partially contradictory findings demonstrate the need for further research on possible transmission routes of C. burnetii between different life stages of ticks and from ticks to their hosts
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