Tissue distribution of Orientia tsutsugamushi in rodents: a molecular and immune diagnostic approach.

BACKGROUND

Scrub typhus is caused by a bacterium Orientia tsutsugamushi, which is transmitted to humans by infected chigger mites found in scrub vegetation. This study examined the tissue distribution of O. tsutsugamushi in rodents collected from different districts in Kerala, India. Tissue tropism helps to understand disease spread to cells and tissues, leading to inflammation and multi-organ failure.

METHODS

O. tsutsugamushi infection was screened using molecular and immunological diagnostic tools in 137 rodents. Of these, 78 were positive for O. tsutsugamushi in blood samples by both molecular and immunological diagnostic methods. Hearts, spleens, livers, and kidneys of positive rodents were sampled using PCR, nested PCR, ELISA, and Western blot.

RESULTS

First-step PCR showed 80.76%, 61.53%, 53.84%, and 62.82% positive for O. tsutsugamushi in liver, spleen, kidney, and heart, respectively. Nested PCR revealed 100%, 85.89%, 73.07%, and 62.82% positive results in liver, spleen, kidney, and heart, respectively. Antibody against recombinant outer membrane protein of O. tsutsugamushi by indirect ELISA showed 86.40% (liver), 77.66% (spleen), 69.90% (kidney), 49.51% (heart), and 74.75% (blood) positive. Western blot showed prominent bands in the liver and spleen, and mild bands in the kidney and heart. IFA supports O. tsutsugamushi antigen detection, demonstrating utility for confirmation and pathogenesis studies.

CONCLUSION

These findings indicate nested PCR is more sensitive for O. tsutsugamushi detection compared to single-step PCR and ELISA. Results suggest that liver, spleen, and blood are selective targets for O. tsutsugamushi and reliable screening tissues, with implications for disease course and treatment.