Molecular diagnosis of scrub typhus: A preliminary report from Pondicherry

Abstract

Scrub typhus is a febrile, zoonotic disease caused by the organism Orientia tsutsugamushi. Early and
precise diagnosis is crucial to reduce the risk of complications of the disease and prevent mortality.
Although serology has remained a mainstay for diagnosis it does not help initial treatment. Nested PCR
offers an early and viable alternative. The objective of our study is to standardise nested PCR for 56 kDa
gene of Orientia tsutsugamushi in the diagnosis of scrub typhus. Nested PCR was performed on 406 EDTA
blood samples with clinically suspected scrub typhus to detect 56kDa gene of Orientia tsutsugamushi.
Weil-Felix test was performed on serum samples for the same patients. Among 406 patients, 51(12.56%)
showed positive by Weil-Felix test against OX-K antigen and 91(22.41%) showed positive by nested PCR.
Among 91 cases which were positive by nested PCR, 68 (74.73%) showed negative by Weil-Felix test. Out of
51 cases positive by Weil-Felix test, 28 (54.90%) cases showed negative by nested PCR. Nested PCR
targeting the Orientia tsutsugamushi specific for 56kDa gene acts as an improved diagnostic tool than WeilFelix test which still remains a mainstay in resource poor settings for diagnosis of scrub typhus.