Serology in chronic Q fever is still surrounded by question marks

Q Fever: An Emerging Reality in Portugal

Q fever is a zoonosis caused by Coxiella burnetii with worldwide distribution at the increasing expression in Europe and endemic in Portugal. It is transmitted by inhalation of aerosols containing spores, main reservoir being cattle, goats and sheep as by ingesting cottage cheese or unpasteurized milk. The majority of patients are asymptomatic; however, they may present with fever, atypical pneumonia, acute hepatitis, cutaneous manifestations and rarely with cardiac or neurological involvement. Although most cases are self-limited, focal persistent or chronic Q fever can manifest years after the onset, wherefore follow-up is essential. The clinical heterogeneity may be so variable that the disease is often diagnosed only if it has been systematically considered. It should be especially taken into account in the presence of risk factors as valvular or joint prostheses, immunocompromised patients, pregnant women and epidemiological setting. The authors present a rare case of Coxiella burnetii pneumonia with cutaneous and hepatic manifestations without any risk factor. This case aims to emphasize the importance of Q fever in the differential diagnosis of fever or atypical pneumonia, even in the absence of known risk factors. The diagnosis is often challenging for clinicians and it is necessary to maintain a high index of suspicion. In Europe and specifically in Portugal is mandatory to report the cases to establish the real impact of this disease.

Recent Advances on the Innate Immune Response to Coxiella burnetii

Coxiella burnetii is an obligate intracellular Gram-negative bacterium and the causative agent of a worldwide zoonosis known as Q fever. The pathogen invades monocytes and macrophages, replicating within acidic phagolysosomes and evading host defenses through different immune evasion strategies that are mainly associated with the structure of its lipopolysaccharide. The main transmission routes are aerosols and ingestion of fomites from infected animals. The innate immune system provides the first host defense against the microorganism, and it is crucial to direct the infection towards a self-limiting respiratory disease or the chronic form. This review reports the advances in understanding the mechanisms of innate immunity acting during C. burnetii infection and the strategies that pathogen put in place to infect the host cells and to modify the expression of specific host cell genes in order to subvert cellular processes. The mechanisms through which different cell types with different genetic backgrounds are differently susceptible to C. burnetii intracellular growth are discussed. The subsets of cytokines induced following C. burnetii infection as well as the pathogen influence on an inflammasome-mediated response are also described. Finally, we discuss the use of animal experimental systems for studying the innate immune response against C. burnetii and discovering novel methods for prevention and treatment of disease in humans and livestock.

Challenging case of chronic Q fever endocarditis: usefulness of 18F-FDG PET/CT in the diagnosis and follow-up

Diagnosis of infective endocarditis can be challenging for clinicians, especially when involving prosthetic valves. Recent data suggest that 18F-fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG PET/CT) could be a useful diagnostic tool in this setting. Here, we report a case of a patient with an aortic biological prosthesis who presented with a history of fever and fatigue. Echocardiograms were negative for vegetations. The 18F-FDG PET/CT revealed an infective process of the valve and serological tests were positive for chronic Coxiella burnetii infection. Specific treatment for chronic Q fever endocarditis was, therefore, started and the response was monitored using 18F-FDG PET/CT. This case highlights the challenges and pitfalls clinicians face when confronted with prosthetic valve endocarditis and the use of 18F-FDG PET/CT for diagnosis and follow-up.

Whole Blood Interferon γ Release Is a More Sensitive Marker of Prior Exposure to Coxiella burnetii Than Are Antibody Responses

For the zoonotic disease Q fever, serological analysis plays a dominant role in the diagnosis of Coxiella burnetii infection and in pre-screening for past exposure prior to vaccination. A number of studies suggest that assessment of C. burnetii-specific T-cell IFNγ responses may be a more sensitive tool to assess past exposure. In this study, we assessed the performance of a whole blood C. burnetii IFNγ release assay in comparison to serological detection in an area of high Q fever incidence in 2014, up to seven years after initial exposure during the Dutch Q fever outbreak 2007-2010. In a cohort of >1500 individuals from the Dutch outbreak village of Herpen, approximately 60% had mounted IFNγ responses to C. burnetii. This proportion was independent of the Coxiella strain used for stimulation and much higher than the proportion of individuals scored sero-positive using the serological gold standard immunofluorescence assay. Moreover, C. burnetii-specific IFNγ responses were found to be more durable than antibody responses in two sub-groups of individuals known to have sero-converted as of 2007 or previously reported to the municipality as notified Q fever cases. A novel ready-to-use version of the IFNγ release assay assessed in a subgroup of pre-exposed individuals in 2021 (10-14 years post exposure) proved again to be more sensitive than serology in detecting past exposure. These data demonstrate that C. burnetii-induced IFNγ release is indeed a more sensitive and durable marker of exposure to C. burnetii than are serological responses. In combination with a simplified assay version suitable for implementation in routine diagnostic settings, this makes the assessment of IFNγ responses a valuable tool for exposure screening to obtain epidemiological data, and to identify previously exposed individuals in pre-vaccination screens.

Current approaches for the detection of Coxiella burnetii infection in humans and animals

Q fever (coxiellosis), caused by Coxiella burnetii, is an emerging or re-emerging zoonotic disease of public health significance and with worldwide distribution. As a causal agent of the one among the 13 global priority zoonoses, having the infectious dose as low as one bacterium, C. burnetii has been regarded as an obligate intracellular bacterial pathogen. The agent has been classified as a Group B bioterrorism agent by the Centre for Disease Control and Prevention (CDC), and the disease is included in the World Organisation for Animal Health (OIE) list of notifiable diseases. It is mainly transmitted through airborne route in humans and animals. Isolation of C. burnetii, using standard routine laboratory culture techniques was impossible until formulation of axenic-based medium. However, it is still to be included among routinely isolated laboratory pathogen, accounting prolonged incubation period (~7 days) and requirement of specific oxygen concentration (2.5% O₂). Therefore, indirect diagnostic tools have been mainly used for its diagnosis. So far serology has been mostly used for testing for C. burnetii infection. The detection of C. burnetii DNA by PCR in various clinical samples have also been widely used. The disease has remained largely under-reported, underdiagnosed and as a masked zoonosis; and therefore, needs to be explored through well-planned scientific studies for knowing its true status and likely it impact in humans and animals by employing state-of-the-art diagnostics, identifying its diverse and new host range, as well as risk factors involved in different geo-climatic, behavioural and social settings as well as risk groups. Here, we reviewed the current approaches used for the detection of C. burnetii infection in humans and animals at the population and individual level.

CXCL9, a promising biomarker in the diagnosis of chronic Q fever

Background

In the aftermath of the largest Q fever outbreak in the world, diagnosing the potentially lethal complication chronic Q fever remains challenging. PCR, Coxiella burnetii IgG phase I antibodies, CRP and ¹⁸F–FDG-PET/CT scan are used for diagnosis and monitoring in clinical practice. We aimed to identify and test biomarkers in order to improve discriminative power of the diagnostic tests and monitoring of chronic Q fever.

Methods

We performed a transcriptome analysis on C. burnetii stimulated PBMCs of 4 healthy controls and 6 chronic Q fever patients and identified genes that were most differentially expressed. The gene products were determined using Luminex technology in whole blood samples stimulated with heat-killed C. burnetii and serum samples from chronic Q fever patients and control subjects.

Results

Gene expression of the chemokines CXCL9, CXCL10, CXCL11 and CCL8 was strongly up-regulated in C. burnetii stimulated PBMCs of chronic Q fever patients, in contrast to healthy controls. In whole blood cultures of chronic Q fever patients, production of all four chemokines was increased upon C. burnetii stimulation, but also healthy controls and past Q fever individuals showed increased production of CXCL9, CXCL10 and CCL8. However, CXCL9 and CXCL11 production was significantly higher for chronic Q fever patients compared to past Q fever individuals. In addition, CXCL9 serum concentrations in chronic Q fever patients were higher than in past Q fever individuals.

Conclusion

CXCL9 protein, measured in serum or as C. burnetii stimulated production, is a promising biomarker for the diagnosis of chronic Q fever.

Electronic supplementary material

The online version of this article (doi:10.1186/s12879-017-2656-6) contains supplementary material, which is available to authorized users.

From Q Fever to Coxiella burnetii Infection: a Paradigm Change

Coxiella burnetii is the agent of Q fever, or "query fever," a zoonosis first described in Australia in 1937. Since this first description, knowledge about this pathogen and its associated infections has increased dramatically. We review here all the progress made over the last 20 years on this topic. C. burnetii is classically a strict intracellular, Gram-negative bacterium. However, a major step in the characterization of this pathogen was achieved by the establishment of its axenic culture. C. burnetii infects a wide range of animals, from arthropods to humans. The genetic determinants of virulence are now better known, thanks to the achievement of determining the genome sequences of several strains of this species and comparative genomic analyses. Q fever can be found worldwide, but the epidemiological features of this disease vary according to the geographic area considered, including situations where it is endemic or hyperendemic, and the occurrence of large epidemic outbreaks. In recent years, a major breakthrough in the understanding of the natural history of human infection with C. burnetii was the breaking of the old dichotomy between "acute" and "chronic" Q fever. The clinical presentation of C. burnetii infection depends on both the virulence of the infecting C. burnetii strain and specific risks factors in the infected patient. Moreover, no persistent infection can exist without a focus of infection. This paradigm change should allow better diagnosis and management of primary infection and long-term complications in patients with C. burnetii infection.

Prevalence of Coxiella burnetii Infection in Humans Occupationally Exposed to Animals in Poland

Coxiella burnetii is the etiological agent of Q fever, and outbreaks of Q fever have been reported in different parts of Europe both in animals and humans. Human infections are mostly associated with infections in ruminants, e.g., sheep, goats, and cows. Various professional groups are occupationally exposed to infection with C. burnetii. The aim of this study was investigate the prevalence of C. burnetii in farm workers. Serum samples were collected from 151 persons from six different regions of Poland. The serum samples were tested using three serological methods--complement fixation test (CFT), enzyme-linked immunosorbent assay (ELISA), and indirect fluorescent antibody (IFA). A total of 71 samples of blood were also tested by real-time PCR. The results showed that antibodies against C. burnetii were present in the tested sera. Average percentages of seropositive samples in IFA, ELISA, and CFT were 31.12%, 39.07%, and 15.23%, respectively. Positive results were noted in each testing center. Of the three test types, IFA results were considered the most sensitive. Real-time PCR confirmed the presence of DNA specific for C. burnetii in 10 patients. The farming workforce constitutes an occupational risk group with an increased risk for C. burnetii infection, presumably because of their contact with infected livestock.