The GroEL Gene Molecular Marker in the Detection of Pathogens Rickettsia conorii subspecies indica at the Species Level in the Ixodidae Ticks Collected from Domestic Animals in Different Agro-Climatic Regions in Tamil Nadu, India

Abstract

Background: Indian tick typhus (ITT) is a type of spotted fever caused by intracellular Rickettsial pathogens, specifi­cally Rickettsia conorii subspecies indica, which exhibits unique clinical symptoms in humans compared to other spot­ted fevers. Human cases have been reported from several states based on hospital-based studies. However, research on the detection of these pathogens in ticks is limited.

Methods: A tick survey was conducted in different agro-climatic regions of Tamil Nadu. A total of 3,016 ticks belong­ing to 12 species in 532 pools were tested for the presence of the groEL gene of Rickettsia conorii indica using indige­nously designed primers.

Results:  Of the 532 pools tested, 44 pools (8.27 %) were positive for the groEL gene, resulting in an overall Minimum Infection Rate (MIR) of 1.50 (95% CI=1.11–1.98). The bacteria were identified in all agro-climatic regions except in the Cauvery delta region. The MIR of the screened tick species were 4.11 (95% CI=1.73–8.43) in Rhipicephalus mi­croplus, 1.34 (95% CI=0.90–1.92) in Haemaphysalis bispinosa, and 2.85 (95% CI=1.56–4.83) in Haemaphysalis inter­media.  The MIR of the ticks collected from cattle was 0.34 in cattle (95% CI=0.15–0.67), 5.50 (95% CI=3.97–7.44) in goats, and 1.37 (95% CI=0.36–3.71) in sheep.

Conclusion: The present study reports that the groEL gene as preliminary marker for the detection of the ITT-causing pathogen in field-collected ticks. The positivity of the groEL gene in the salivary glands needs further experimental con­firmation. The primer needs further evaluation by comparing with MLST (Multilocus sequence typing) sequencing.