In the Search of Potential Serodiagnostic Proteins to Discriminate Between Acute and Chronic Q Fever in Humans. Some Promising Outcomes

Abstract

Coxiella burnetii is the agent that causes acute and chronic Q fever infections in humans. Although the isolates studied so far have shown that the two forms of the disease differ in virulence potential thus, implying a variance in their proteomic profile, the methods used do not deliver enough discriminatory capability and often, human infections may be mis-diagnosed. The current study adds further knowledge to the results that we have already published on the Coxiella outer membrane protein 1 (Com1). Herein we identified the proteins GroEL, Ybgf, OmpH, and UPF0422 as candidates for serodiagnostics of Q fever; following cloning, expression and purification they were further used as antigens in ELISA for the screening of patients' sera associated with chronic Q fever endocarditis, sera negative for phase I IgG, sera with at least one sample positive for phase I IgG and sera from patients who suffered from various rheumatic diseases. Blood donors were used as the controls. Sensitivity, specificity, positive predictive value, negative predictive value, and Cohen's kappa coefficient (κ) were calculated and we also performed binary logistic regression analysis to identify combinations of proteins with increased diagnostic yield. We found that proteins GroEL and Ybgf, together with Com1, play the most significant role in the correct diagnosis of chronic Q fever. Of these three proteins, it was shown that Com1 and GroEL present the highest sensitivity and specificity altogether. The results add to the existing knowledge that an antigen-based serodiagnostic test that will be able to correctly diagnose chronic Q fever may not be far from reality.

Development of High-Throughput Multiplex Serology to Detect Serum Antibodies against Coxiella burnetii

“…GroEL and DnaK were also persistent and accurate molecular markers described by Xiong et al [32,37,44,[46][47][48]. Using multiplex serology, they achieved specificities of 84% and 79%, respectively, and sensitivities of 79% and 68%, respectively.…”

Identification of Immunogenic Linear B-Cell Epitopes in C. burnetii Outer Membrane Proteins Using Immunoinformatics Approaches Reveals Potential Targets of Persistent Infections

“…Moreover, 77% of the C. burnetii-reactive group was also reactive to at least one of the identified epitopes (Table 4). These data reinforce the need to identify linear B-cell epitopes in other promising serological markers-such as OmpA [89], C. burnetii macrophage infectivity potentiator protein (Cb-Mip) [90], and YbgF [85]-in order to improve the development of novel tools for the diagnosis of C. burnetii.…”

“…Moreover, despite the possibility of mistaking Q fever for influenza, dengue, malaria, leptospirosis, and other infectious diseases [30], in Brazil, only suspected rickettsiosis cases are investigated as Q fever, corroborating the underreporting of this zoonosis, and explaining the limited number of C. burnetii-reactive samples in this study (n = 26). Remarkably, similar-sized samples were previously used to successfully define C. burnetii proteins as antigens to serological tests [37,[84][85][86], indicating that the number of patients used in our study was sufficient to prove the natural immunogenicity of the identified epitopes.…”

Characterization of recombinant Ybgf protein for the detection of Coxiella antibodies in ruminants

“…31 This Com1 antigen study found a Se of 77% and Sp of 72%, without significant differences among species (sheep, goat, and cattle), 31 although Com1 is reported to be more sensitive and specific than Ybgf in humans. 16,25,31 This discrepancy might be attributed to different immune responses against these antigens between humans and ruminants, as well as the choice of sera used for the assay. Certainly, our ELISA is not a useful tool for routine testing, but further experiments are needed to compare the results with a larger number of true-positive and true-negative sera.…”

“…38 In human medicine, recent attempts to use Ybgf in a recombinant ELISA revealed good Sp (close to 90%) but poor Se (12.5-21%). 16,25 We evaluated the efficiency of this recombinant antigen for the detection of antibodies against Coxiella burnetii in ruminants.…”