1. What specimens were used for the PCR for rickettsiosis? Is serology the gold standard for diagnosis?
For PCR specimens, you will need the buffy coat from blood, or biopsy of the eschar, or swab of the eschar (if eschar is present).
Serology is the gold standard, more specifically IFA (immunofluorescense assay) due to its high sensitivity.
2. In clinical labs, PCR is not widely available, increasingly, the reference labs, we used to have indirect immunoperoxidase test but this has been discontinued, I’ve heard that commercial ELISA is now available, is it useful?
They can be but I have not tried any personally. The labs we work with tend to have their own ELISA assays they developed in-house.
3. Any reasons why no eschar was found?
Eschars may or may not be present. Reason for eschars forming is not yet ascertained. It can be as a result of a number of different reasons, such as infection of the epidermal layer around the bite site did not take hold, i.e. rickettsial pathogens is infecting the patient through the vascular system, size of infectious dose, duration of arthropod attachment to the patient, underlying conditions etc.
4. Any relation to the post tick bite Lyme's disease in US?
No relation at all. Lyme disease is caused by members of the genus Borrelia. A different type of bacteria from Rickettsia and Orientia. Though they may share similar vectors and mode of transmission, the biology of the two organisms are very dissimilar, and so is the disease aetiology caused by both pathogens. Ticks are notorious for being reservoirs and vectors for many types of pathogens including viruses. We still continue to discover these pathogens today.
Dr. Mohammad Yazid Abdad holds the post of Senior Scientific Officer in the Infectious Disease Research Laboratory of the National Centre for Infectious Diseases Singapore, where he is the Senior Scientist and provides scientific and Biosecurity/Biosafety advice to ongoing projects. He is also actively involved in a number of projects as PI, Co-PI and collaborator investigating SARS-COV-2 (COVID-19), carbapenem resistant Enterobacteriaceae, bacteriophages, respiratory diseases and rickettsial diseases. Since his research career began, Yazid has published 27 papers in peer-reviewed journals and authored a book chapter on Rickettsia. He discovered and characterized a new species of bacteria, Rickettsia gravesii, and tick, Ixodes woyliei. He also isolated and characterized the first description of Barmah Forest virus outside of Australia.