Development and validation of a real-time reverse transcriptase PCR assay for sensitive detection of SFTSV

Development of an all-in-one real-time PCR assay for simultaneous detection of spotted fever group rickettsiae, severe fever with thrombocytopenia syndrome virus and hantaan virus prevalent in central China

Central China has been reported to be one of the most important endemic areas of zoonotic infection by spotted fever group rickettsiae (SFGR), severe fever with thrombocytopenia syndrome virus (SFTSV) and hantaan virus (HTNV). Due to similar clinical symptoms, it is challenging to make a definite diagnosis rapidly and accurately in the absence of microbiological tests. In the present study, an all-in-one real-time PCR assay was developed for the simultaneous detection of nucleic acids from SFGR, SFTSV and HTNV. Three linear standard curves for determining SFGR-ompA, SFTSV-L and HTNV-L were obtained within the range of 101-106 copies/μL, with the PCR amplification efficiencies ranging from 93.46% to 96.88% and the regression coefficients R2 of >0.99. The detection limit was 1.108 copies/μL for SFGR-ompA, 1.075 copies/μL for SFTSV-L and 1.006 copies/μL for HTNV-L, respectively. Both the within-run and within-laboratory coefficients of variation on the cycle threshold (Ct) values were within the range of 0.53%-2.15%. It was also found there was no statistical difference in the Ct values between single template and multiple templates (PSFGR-ompA = 0.186, PSFTSV-L = 0.612, PHTNV-L = 0.298). The sensitivity, specificity, positive and negative predictive value were all 100% for determining SFGR-ompA and SFTSV-L, 97%, 100%, 100% and 99.6% for HTNV-L, respectively. Therefore, the all-in-one real-time PCR assay appears to be a reliable, sensitive, rapid, high-throughput and low cost-effective method to diagnose the zoonotic infection by SFGR, SFTSV and HTNV.

Advancements in the Worldwide Detection of Severe Fever with Thrombocytopenia Syndrome Virus Infection from 2009 to 2023

Severe fever with thrombocytopenia syndrome (SFTS) is a growing concern as an emerging tick-borne infectious disease originating from the SFTS virus (SFTSV), a recent addition to the Phlebovirus genus under the family of bunyaviruses. SFTS is typically identified by symptoms such as fever, thrombocytopenia, leukopenia, and gastrointestinal problems, accompanied by a potentially high case fatality rate. Thus, early and accurate diagnosis is essential for effective treatment and disease management. This review delves into the existing methodologies for SFTS detection, including pathogenic, molecular, and immunological technologies.

Carbon black as a colorimetric label for an immunochromatographic test strip for severe fever with thrombocytopenia syndrome virus detection

To combat the ongoing threat posed by severe fever with thrombocytopenia syndrome virus (SFTSV), especially in underserved areas, there is an urgent need for an affordable and reliable point-of-care diagnostic tool. This study presents a carbon black-based immunochromatographic test strip (CB-ICTS) for the detection of SFTSV, which is both quick and easy to operate. The study optimized the specific steps for carbon black-labeled antibodies, as well as the amount of carbon black and anti-SFTSV antibody used. Under optimal experimental conditions, the linear range and limit of detection of the CB-ICTS were evaluated using different concentrations of SFTSV standard samples. The detection range of the CB-ICTS for SFTSV was found to be 0.1-1000 ng mL^-1, with a limit of detection of 100 pg mL^-1. The precision and accuracy of the CB-ICTS were assessed by examining spiked healthy human serum samples, which displayed recoveries ranging from 91.58 to 105.4% with a coefficient of variation of less than 11%. This work evaluated the specificity of the CB-ICTS using various biomarkers (CA125, AFP, CA199, CEA, and HCG) and demonstrated that the CB-ICTS is highly specific for detecting SFTSV, suggesting its potential for the early diagnosis of SFTSV. In addition, the study evaluated the CB-ICTS in serum samples from patients with SFTSV, and the results were highly consistent with those detected by the polymerase chain reaction (PCR) method. Overall, this study demonstrates the feasibility and effectiveness of using the CB-ICTS as a reliable point-of-care diagnostic tool for the early detection of SFTSV.

Rapid detection of the emerging tick-borne Tamdy virus by TaqMan-based real-time reverse transcription PCR

Tamdy virus (TAMV) is an emerging zoonotic tick-borne arbovirus in the genus Orthonairovirus. Reports of human infections with TAMV have been increasing and development of a rapid detection assay is thus urgently required. In the present study, singleplex and dual-target real-time reverse transcription PCR (qRT-PCR) assays were established for the detection of TAMV. Sensitivity and specificity were evaluated and demonstrated high sensitivity of both the singleplex and dual-target qRT-PCR assays with no cross-reaction with common bunyaviruses and tick-borne viruses. The TaqMan-based qRT-PCR methodology established in this study can be employed for epidemiological surveillance and pathogenesis studies of TAMV.

Sex Differences in Case Fatality Rate of Patients With Severe Fever With Thrombocytopenia Syndrome

Background: Severe fever with thrombocytopenia syndrome (SFTS) is a tick-borne disease with high mortality. However, detailed analysis is lacking to explore the complex effect of sex with age or comorbidities. Methods: A retrospective cohort study was performed among 2,938 SFTS patients entered during 2011-2020 in Xinyang, China. The case fatality rate (CFR) was estimated for their association with sex, age, and comorbidities by an interactive way. The difference of immune response between sex was explored in an age dependent way. Results: An overall CFR of 15.3% (450/2,938) was obtained, which appeared to be higher in males than in females [17.7% vs. 13.6%, adjusted odds ratio (aOR) = 1.24; 95% CI, 1.00-1.53; P = 0.048] and increased dramatically with age (P < 0.001). The associations between sex and SFTS fatal outcome were age-dependent and varied according to the status of comorbidities. The mortality-related risk conferred by older age was more pronounced in males, with aOR (95% CI) to be 5.76 (3.75-8.84) vs. 5.30 (3.54-7.95) in female. Sex-stratified analysis disclosed significant associations between death and comorbidities among female patients (aOR = 1.87, 95% CI: 1.40-2.49; P < 0.001), while none among males. Among females, the significant associations between presence of comorbidity and fatal outcome differed among age groups, with aOR (95% CI) decreased from 2.28 (1.16-4.46) in ≤60 years, to 2.06 (1.34-3.18) in 60-70 years and further to 1.55 (0.97-2.47) in >70 years. Altogether 194 SFTS patients were randomly selected for the test of B cells, natural killer (NK) cells, CD4 cells percentages, and anti-SFTSV IgM antibody level, the results revealed that males >60 years had significantly decreased percentages of B cells, CD4 cells, lower anti-SFTSV IgM antibody titer, and increased level of NK cells than male aged ≤60 years, while none of these age specific differences was observed in the females. This finding underlies the more pronounced age specific difference in CFR among male than female. Conclusions: Males had a significantly higher mortality of SFTS than did females, and more likely to be affected by aging for SFTS mortality. This difference can be explained by the effect from comorbidities and the host immunity. It is essential to take a sex- and age-based approach to SFTS treatment and management.