The Prevalence of Coxiella burnetii in Hard Ticks in Europe and Their Role in Q Fever Transmission Revisited—A Systematic Review

Abstract

The zoonosis Q fever is caused by the obligate intracellular bacterium Coxiella burnetii. Besides the main transmission route via inhalation of contaminated aerosols, ticks are discussed as vectors since the first isolation of the pathogen from a Dermacentor andersonii tick. The rare detection of C. burnetii in ticks and the difficult differentiation of C. burnetii from Coxiella-like endosymbionts (CLEs) are questioning the relevance of ticks in the epidemiology of Q fever. In this review, literature databases were systematically searched for recent prevalence studies concerning C. burnetii in ticks in Europe and experimental studies evaluating the vector competence of tick species. A total of 72 prevalence studies were included and evaluated regarding DNA detection methods and collection methods, country, and tested tick species. Specimens of more than 25 different tick species were collected in 23 European countries. Overall, an average prevalence of 4.8% was determined. However, in half of the studies, no Coxiella-DNA was detected. In Southern European countries, a significantly higher prevalence was observed, possibly related to the abundance of different tick species here, namely Hyalomma spp. and Rhipicephalus spp. In comparison, a similar proportion of studies used ticks sampled by flagging and dragging or tick collection from animals, under 30% of the total tick samples derived from the latter. There was no significant difference in the various target genes used for the molecular test. In most of the studies, no distinction was made between C. burnetii and CLEs. The application of specific detection methods and the confirmation of positive results are crucial to determine the role of ticks in Q fever transmission. Only two studies were available, which assessed the vector competence of ticks for C. burnetii in the last 20 years, demonstrating the need for further research.

Tick exposure and risk of tick‐borne pathogens infection in hunters and hunting dogs: a citizen science approach

“…Moreover, the detection of R. raoultii , R. aeschlimannii and R. monacensis in ticks collected from dogs suggests their role as indicators of potential human exposure to pathogens in hunting areas (Guggione et al., 2021; Madeddu et al., 2012; Tosoni et al., 2016), and their increased occurrence in southern part of the Italian peninsula (Gomez‐Barroso et al., 2019). The occurrence of C. burnetii in D. marginatus collected on hunting dogs is of public health concern, since the prevalence of this bacterium in hard ticks is significantly higher in Mediterranean area than in other European countries (Körner et al., 2021). Although the vectorial competence of D. marginatus for C. burnetii (via faecal excretion—Körner et al., 2020) has been ascertained, the role of this tick species in the epidemiology of Q fever appears negligible compared to Hyalomma lusitanicum , in which the prevalence of this pathogen (i.e., 18%) is higher than in D. marginatus (i.e., 1.4%) around Europe (Körner et al., 2021).…”

“…The occurrence of C. burnetii in D. marginatus collected on hunting dogs is of public health concern, since the prevalence of this bacterium in hard ticks is significantly higher in Mediterranean area than in other European countries (Körner et al., 2021). Although the vectorial competence of D. marginatus for C. burnetii (via faecal excretion—Körner et al., 2020) has been ascertained, the role of this tick species in the epidemiology of Q fever appears negligible compared to Hyalomma lusitanicum , in which the prevalence of this pathogen (i.e., 18%) is higher than in D. marginatus (i.e., 1.4%) around Europe (Körner et al., 2021). The finding of B. lusitaniae in I. ricinus infesting hunters and hunting dogs confirms the presence of this zoonotic genospecies in rural areas of southern Italy, as previously established in lizards (Mendoza‐Roldan et al., 2019) and foxes (Sgroi et al., 2021).…”

Metagenomic Investigation of Ticks From Kenyan Wildlife Reveals Diverse Microbial Pathogens and New Country Pathogen Records

“…C. burnetii is the etiologic agent of Q fever, characterized by febrile and respiratory symptoms. Infections are zoonotic and are initiated by inhalation of particles contaminated by infected animals, most commonly sheep, goats, and cattle, with ticks implicated in transmission (Körner et al, 2021). E. coli and P. mirabilis are Gram-negative bacteria classified in the family Enterobacteriaceae alongside other potential pathogenic species in the genera Klebsiella, Enterobacter, Citrobacter, Salmonella, Shigella, and Serratia.…”

Contemporary diagnostics for medically relevant fastidious microorganisms belonging to the genera Anaplasma,Bartonella,Coxiella,OrientiaandRickettsia

“…The main cause of human infection is indirect contact with infected small ruminants via airborne or droplet transmission routes, which is possible up to a distance of 10 km and in extreme conditions even up to 18 km (Hawker et al 1998 ; Clark and Soares Magalhães 2018 ). The role of ticks as a disease-carrying vector has not yet been fully elucidated (Körner et al 2021 ).…”