Pulmonary pathology in patients associated with scrub typhus.

Aims: Scrub typhus is a zoonotic disease caused by Orientia tsutsugamushi. Severe cases resulting in mortality from this disease have rarely been reported. We present two scrub typhus cases (a man and a girl) who died of acute respiratory distress syndrome (ARDS).

Methods: Autopsies were performed. Histopathological and immunohistochemical stains were employed using specific antibody for O. tsutsugamushi and inducible nitric oxide synthase (iNOS).

Results: These subjects developed respiratory distress shortly after admission, and expired following respiratory failure. At autopsy, generalised lymphadenopathy was observed. The lung weight was about two-fold the normal value. Gross inspection revealed oedematous and haemorrhagic lungs. Microscopic examination revealed diffuse alveolar damage with hyaline membrane formation and interstitial pneumonitis with infiltration of inflammatory cells. Immunohistochemical stain showed O. tsutsugamushi antigen depositions in the endothelial cells. We also demonstrated iNOS in the alveolar macrophages and lung tissue debris in both cases.

Conclusion: Scrub typhus is usually a mild infectious disease. Our cases present the most dramatic example of sudden death due to ARDS in a short period of time. The clinical investigation and analysis suggest direct endothelial cell invasion of the organism and marked iNOS expression may be involved in the pathogenesis of ARDS associated with scrub typhus.