Background: Rickettsialpox is a febrile illness caused by the mite-borne pathogen Rickettsia akari. Several cases of this disease are reported worldwide annually. Nevertheless, the relationship between the immunogenicity of R. akari and disease development is still poorly understood. Thus, misdiagnosis is frequent. Our study is aiming to identify immunogenic proteins that may improve disease recognition and enhance subsequent treatment. To achieve this goal, two proteomics methodologies were applied, followed by immunoblot confirmation. Results: Three hundred and sixteen unique proteins were identified in the whole-cell extract of R. akari. The most represented protein groups were found to be those involved in translation, post-translational modifications, energy production, and cell wall development. A significant number of proteins belonged to amino acid transport and intracellular trafficking. Also, some proteins affecting the virulence were detected. In silico analysis of membrane enriched proteins revealed 25 putative outer membrane proteins containing beta-barrel structure and 11 proteins having a secretion signal peptide sequence. Using rabbit and human sera, various immunoreactive proteins were identified from which the 44 kDa uncharacterized protein (A8GP63) has demonstrated a unique detection capability. It positively distinguished the sera of patients with Rickettsialpox from other rickettsiae positive human sera. Conclusion: Our proteomic analysis certainly contributed to the lack of knowledge of R. akari pathogenesis. The result obtained may also serve as a guideline for a more accurate diagnosis of rickettsial diseases. The identified 44 kDa uncharacterized protein can be certainly used as a unique marker of rickettsialpox or as a target molecule for the development of more effective treatment.

New way of purification of pathogenic rickettsiae reducing health risks

Background: Rickettsialpox is a febrile illness caused by the mite-borne pathogen Rickettsia akari. Several cases of this disease are reported worldwide. Nevertheless, the relationship between the immunogenicity of R. akari and the disease development remains poorly understood. Therefore, misdiagnosis is frequent. Our study is aimed to identify immunogenic proteins that may improve disease recognition and enhance subsequent treatment. To achieve this goal, two proteomics methodologies were applied, followed by immunoblot confirmation. Results: Three hundred and sixteen unique proteins were identified in the whole-cell extract of R. akari. The most represented protein groups were found to be those involved in translation, post-translational modifications, energy production, and cell wall development. A significant number of proteins belonged to amino acid transport and intracellular trafficking. Also, some proteins affecting the virulence were detected. In silico analysis of membrane enriched proteins revealed 25 putative outer membrane proteins containing beta-barrel structure and 11 proteins having a secretion signal peptide sequence. Using rabbit and patient sera, various immunoreactive proteins were identified from which the 44 kDa uncharacterized protein (A8GP63) has demonstrated a unique detection capability. It positively distinguished the sera of patients with Rickettsialpox from other rickettsia positive patient sera. Conclusion: Our proteomic analysis certainly contributed to the knowledge of the pathogenesis of R. akari. The result obtained may also serve as a guideline for a more accurate diagnosis of rickettsial diseases. Identified R. akari antigenic protein can be design as a unique marker of rickettsialpox and used as a target for the development of more effective treatment.

Diagnosis of rickettsial infections is challenging due to nonspecific clinical symptoms and limitations of current diagnostic methods. Molecular assays allow early detection but are limited by cost and technical demands, whereas conventional serological tests often exhibit cross-reactivity and low sensitivity during the early stages of infection. This study aimed to develop and evaluate a recombinant-antigen sandwich ELISA for improved antibody detection against Rickettsia spp. Three Rickettsia akari proteins, rGroEL, rDnaK, and rA8GP63 (uncharacterized protein), were produced and validated for immunogenicity. The assay was evaluated using 94 patient serum samples, including those with positive, negative, and unknown clinical course. The optimized ELISA demonstrated high reproducibility, with IgG sensitivity of 89.47–95.39% and specificity of 90%. IgM detection, also assessed, showed lower sensitivity (42.11–82.89%) but maintained strong specificity (83.33%). The diagnostic performance was comparable to that of a commercial indirect immunofluorescence assay, with no cross-reactivity detected in sera from patients with unrelated infections. rDnaK and rA8GP63 represent newly explored diagnostic candidates. These findings highlight the potential of this recombinant protein-based ELISA as an accessible, sensitive and specific diagnostic tool, with a meaningful clinical impact for improving the early and accurate detection of rickettsial infections.