Proteomic analysis of Rickettsia akari proposes a 44 kDa-OMP as a potential biomarker for Rickettsialpox diagnosis

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.

Investigating the histopathological findings and immunolocalization of rickettsialpox infection in skin biopsies: A case series and review of the literature

BACKGROUND

Recognition of rickettsialpox infection on skin biopsy can be challenging. The histopathology is non-specific and inconsistently described. We assess classic histopathologic features in confirmed cases and review the literature.

METHODS

We searched for cases of "rickettsialpox" diagnosed between 2006 and 2018 with positive immunostaining for Spotted Fever Group Rickettsia species. Original slides were evaluated for vacuolar alterations, granulomatous inflammation, vasculitis, necrosis, fibrin thrombi, microvesiculation, papillary dermal edema, and extravasated red blood cells. All biopsies were stained for CD3, CD20, CD68, and myeloperoxidase.

RESULTS

Six biopsy specimens were compiled, three of which were sampled from vesiculopapules, one from a maculopapule, and two from eschars. Vacuolar alterations and vasculitis were present in all specimens (6/6; 100%). Granulomatous inflammation was present in five specimens (5/6; 83.3%). Fibrin thrombi and red blood cells were seen in 3/6 (50%) of specimens. The eschars showed necrosis of the epidermis and superficial dermis (2/6, 33.3%). Only one specimen showed intraepidermal vesiculation and papillary dermal edema (1/6; 16.7%). All six specimens showed perivascular infiltration with CD3+ T-cells, and low amounts of CD20+ B-cells and neutrophils. Five of the six specimens (83.3%) showed significant levels of CD68+ histiocytes.

CONCLUSION

The histopathology of rickettsialpox infection is septic lymphocytic and granulomatous vasculitis.