Isolation and identification of R. raoultii in human cases: a surveillance study in three medical centers in China

Abstract

Background

Rickettsia raoultii was frequently detected in multiple tick species, while human infection remained scarcely studied.

Methods

A surveillance study was performed at 3 sentinel hospitals in China, to recruit participants with suspected tick exposure. R. raoultii infection was identified through PCR followed by sequencing and confirmed serologically. Isolation by cell culture was performed and the isolates were genome sequenced.

Results

Twenty-six subjects with R. raoultii infection was determined, including 7 with asymptomatic infection, 15 with mild to moderate illness, and 4 with severe illness. Common nonspecific manifestations in the 19 patients included fever (100%), malaise (95%), myalgia (58%), lymphadenopathy (53%), and nausea (42%). Only 5% of them had rash and 16% had eschar. Scalp eschar and neck lymphadenopathy after a tick bite syndrome was only seen in 2 patients. Of the 4 patients with severe complications, 3 developed pulmonary oedema, and 1 developed clouding of consciousness and lethargy. Frequent abnormalities of laboratory testing included leukopenia, thrombocytopenia, lymphopenia, neutropenia, hypoproteinemia, and elevated levels of total bilirubin, hepatic aminotransferases, lactate dehydrogenase, and creatine kinase. All the 19 patients recovered without sequelae after receiving doxycycline treatment. Two R. rauoltii strains were isolated, and a significantly less degraded genome was observed than other more virulent Rickettsia strains, indicating a low pathogenicity of the current strain.

Conclusions

Human infection with R. raoultii has a wide clinical spectrum that ranged from subclinical infection to severe complications. Physicians need to be aware of the high potential and clinical complexity of R. raoultii infection, to ensure appropriate testing and treatment in endemic regions.