Usefulness of Nested PCR Assay for the Molecular Diagnosis of Human Rickettsial Infection: A Study in Bangladesh

Background: Rickettsial infections are re-emerging arthropods born worldwide zoonotic disease caused by Rickettsia, which is responsible for spotted fever and typhus fever. The diagnosis of a rickettsial illness is important for appropriate antibiotic treatment.

Aims: The study aimed to determine the diagnostic accuracy and clinical usefulness of using nested polymerase chain reaction (PCR) by comparing nested PCR, ELISA, and Weil-Felix (WF) tests.

Methodology: This was a prospective type of cross-sectional study. A total of 135 clinically suspected rickettsial infection cases were enrolled. Peripheral blood was taken to detect gltA, 17 kDa lipoprotein antigen gene (17 kDa), ompA, and ompB gene of Rickettsia by nested PCR. ELISA and Weil-Felix tests were done to compare with nested PCR.

Results: Out of 135 cases, we detected Rickettsia in 70(51.85%) cases by nested PCR assay (p<0.01), 33((24.4%) by Weil- Felix test, 34 (25.18%) by ELISA. Only 26.66% of cases were PCR positive, which were negative by both ELISA and Weil-Felix test. Fifteen (11.11%) cases were positive by all three tests. Among 70 PCR positive rickettsia cases most frequently detected gene was ompB 42(60%), followed by 17kDa 34(48.58%); gltA 21(30%), and ompA 3(4.28%). Multiple gene combinations (ompB, 17kDa and gltA) detected in 98.57 % cases.

Conclusion: Nested PCR assays showed the highest rate of detection of rickettsia cases than ELISA and Weil-Felix test. Multiple gene combinations (ompB, 17kDa, and gltA) showed the highest positivity. Therefore, diagnosis of rickettsial infection can be confirmed by PCR assay, and clinicians can plan appropriate treatment for these patients.