Investigation Of Spotted Fever Group Rickettsia In The Epidemic Region Of Severe Fever With Thrombocytopenia Syndrome

Objective: To evaluate Severe Fever with Thrombocytopenia Syndrome virus and Spotted Fever Group Rickettsia infection in the epidemic region.Methods: An epidemiological survey of patients who met the inclusion criteria was performed.Those patients collected from Kuandian,Fengcheng and the first Affiliated Hospital of China Medical University.Every patient’s clinical data and the blood sample were collected by staff.Serum SFTSV nucleic acid was quantitatively evaluated by Real-time fluorescence quantitative Polymerase Chain Reaction(RT-FQ-PCR).SFGR-specific nucleic acid fragments were amplified from the collected whole blood samples,the amplified products were sequenced,and the sequencing results were analyzed.Results: A total of 136 cases were collected from April to November 2019,and the number of cases that ultimately met the SFTS diagnostic criteria was 40.The majority of the patients were farmers(82.5%),including 26 female patients(65%).The age(mean ± SD)was 61.35±11.49 years old.The onset month was from April to October,the body temperature(mean ± SD)was 38.8±0.48℃,and the viral load(mean ± SD)was 6.14±0.89 Log10 copies/ml.There was a negative correlation between viral load and platelet count in SFTS patients,and the lower the platelet count was,the higher the viral load was(r=-0.34,p<0.05).The platelet count in severe patients was 39.5(29.3-49.3)×10^9/L,and the viral load was 7.13±0.89 Log10 copies/ml.The platelet count in non-severe patients was 58.0(40.0-77.0)×10^9/L,and the viral load was 5.79±0.64 Log10 copies/ml.The platelet count of patient in the severe group was lower than that in the non-severe group(p=0.023).The viral load of patient in the severe group was higher than that in the non-severe group(p <0.001).The whole blood samples of 96 patients were screened for SFGR,and rickettsia-specific glt A(381bp)and omp A(346bp)gene fragments were amplified by PCR.One case of spotted fever group rickettsia was finally detected.Sequencing analysis confirmed that the pathogen was Rickettsia parkeri strain Atlantic rainforest.Conclusion: The viral load of patients with severe SFTS is higher than 10^6 copies/ml.It suggested that high viral load was a risk factor for the disease progression of SFTS.All confirmed SFTS patients showed clinical manifestations of fever and thrombocytopenia,and there was a negative correlation between platelet count and viral load.By screening collected specimens for SFGR,we have identified China’s first laboratory-confirmed case of infection with the Rickettsia parkeri strain Atlantic rainforest.No combined infection of SFTSV and SFGR was found in this study.