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Prediction of rickettsial skin eschars in humans using an experimental guinea pig model
Bernard La Scola1, Yassina Bechah, Hubert Lepidi
1URMITE, CNRS UMR, IRD, IFR, Université de la Méditerranée, Marseille, France.
Abstract:
Until now, when a new Rickettsia species was isolated in a tick, it was not possible to predict whether it was a human pathogen or if it would cause a skin eschar at the infection site. Guinea pigs are injected intradermally with 25 different Rickettsia species or subspecies: 16 induced an eschar, 5 induced inflammatory lesions and 4 have no effect. We observed that the occurrence of skin eschars in this model was significantly correlated (P <0.05) with observations of skin eschars in humans (14/16). The most common histological finding was mononuclear cell infiltration. Polymorphonuclear cell infiltration was observed for Rickettsia australis, Rickettsia japonica, and, as in humans, Rickettsia africae. The treatment of guinea pigs with corticosteroids prevents the apparition of eschar following Rickettsia bellii inoculation. Virulent, but not avirulent, Rickettsia prowazekii induced transient inflammatory lesions that were associated with dermal vasculitis, as is Rickettsia typhi. Therefore, the intradermal injection of Rickettsia in guinea pigs appears to be a relevant model for the prediction of the development of escharotic lesions following Rickettsia infection in humans. We speculate that skin eschar is the reflect of a local control avoiding extreme virulence.
Insights
This study introduces a new guinea pig model for predicting Rickettsia infections. Intradermal Rickettsia injections in guinea pigs correlate with human eschar development, aiding pathogen identification.
Area of Science:
- Microbiology
- Veterinary Pathology
- Infectious Diseases
Background:
- Predicting the pathogenicity of novel Rickettsia species in ticks has been challenging.
- Determining if an isolated Rickettsia species will cause a human skin eschar was previously not possible.
Purpose of the Study:
- To establish a relevant animal model for predicting Rickettsia-induced eschar development in humans.
- To assess the correlation between Rickettsia infection in guinea pigs and human clinical outcomes.
Main Methods:
- Intradermal inoculation of 25 different Rickettsia species/subspecies into guinea pigs.
- Observation of lesion development (eschar, inflammatory, or no effect) in guinea pigs.
- Histological examination of lesions and correlation with human observations.
Main Results:
- 16 Rickettsia species induced eschars, 5 induced inflammatory lesions, and 4 had no effect in guinea pigs.
- Guinea pig eschar development significantly correlated with human eschar formation (14/16 cases).
- Mononuclear cell infiltration was common; polymorphonuclear infiltration occurred with specific species (e.g., R. australis, R. japonica, R. africae).
Conclusions:
- Intradermal Rickettsia injection in guinea pigs serves as a relevant model for predicting human eschar development.
- The model aids in identifying potentially pathogenic Rickettsia species.
- Skin eschar formation may indicate localized control of extreme virulence.
