By Dean L. Winslow, MD, FACP, FIDSA

Professor of Medicine, Division of General Medical Disciplines, Division of Infectious Diseases and Geographic Medicine, Stanford University School of Medicine

Dr. Winslow reports no financial relationships relevant to this field of study.

SYNOPSIS: Fifty-six of 733 patients in China who were evaluated for suspected Severe Fever with Thrombocytopenia Syndrome (SFTS) were shown by polymerase chain reaction (PCR) to be infected with Candidatus Rickettsia tarasevichiae (CRT). Fever, myalgia, cough, gastrointestinal symptoms, and hemorrhagic manifestations were common. Rash was rarely seen, and eschar was observed in 16% of cases. Thrombocytopenia, leukopenia, and abnormal LFTs were commonly observed. Co-infection with SFTS virus was seen 66% of patients, and eight patients died.

SOURCE: Liu W, Li H, Lu QB, et al. Candidatus Rickettsia tarasevichiae infection in Eastern Central China: A case series. Ann Intern Med 2016;164: 641-648.

From April until November 2014, patients with suspected SFTS were recruited for prospective study at a People’s Liberation Army sentinel hospital in Eastern Central China. Seven hundred thirty-three patients were admitted to the hospital and had specimens collected. Blood specimens were analyzed by PCR for spotted fever group (SFG) rickettsiae, Anaplasmataceae, Borrelia, and Babesia. Candidatus Rickettsia tarasevichiae (CRT) infection was confirmed by sequencing of the ompA-coding gene.

All 56 patients with CRT infection presented with a febrile illness. Other common manifestations included gastrointestinal symptoms, nonspecific neurologic symptoms, hemorrhagic signs, and plasma leakage. Lymphadenopathy was present in 29% of patients. Rash was present in only 4% of patients and eschar in 16%. Sixty-six percent were co-infected with SFTSV, and 14% died. Leukopenia was present in 59%, thrombocytopenia in 70%, lymphopenia in 45%, elevated transaminases or LDH in 54-82%, elevated CK in 46%, and elevated BUN in 20%. Laboratory abnormalities peaked in most patients about 10 days after symptom onset.

Only 27% of patients reported a history of tick bite, but 100% worked as farmers. A total of 397 adult Haemaphysalis longicornis ticks were captured, and 8.3% tested positive for CRT, while 9.3% had positive SFTSV test results. Peak numbers of cases occurred in June, July, and August.

COMMENTARY

“New” tick-associated rickettsial pathogens are being increasingly recognized around the world. In China, eight emerging Rickettsia species have been identified. CRT, R. sibirica, R. raoultii, and R. heilongjiangiensis are known to cause human disease.1 In 2009, a novel tick-borne viral infection associated with severe fever and thrombocytopenia was recognized in Central Eastern China.2 SFTS virus is a bunyavirus of the genus Phlebovirus and has resulted in thousands of cases of human disease in 19 of 32 Chinese provinces. While the clinical and laboratory manifestations of patients shown to be infected with CRT are nonspecific, many of the patients appeared to be as ill as patients with Rocky Mountain Spotted Fever, and more ill than most patients with R. conorii SFG rickettsial disease. The clinical overlap with SFTSV and the common occurrence of co-infection with SFTSV and CRT in patients in China should be appreciated. Use of rapid molecular diagnostic methods to diagnose CRT (and other rickettsioses) and empiric use of doxycycline should be considered in appropriate patients. 

REFERENCES

  1. Fang LQ, et al. Emerging tick-borne infections in mainland China: An increasing public health threat. Lancet Infect Dis 2015;15:1467-1479.
  2. Yu XJ, et al. Fever with thrombocytopenia associated with a novel bunyavirus in China. N Engl J Med 2011;364:1523-1532.