Background: Scrub typhus is a neglected rickettsial vector-borne disease especially prominent in Asia Pacific region caused by pathogen Orientia tsutsugamushi which is a gram negative obligate intracellular parasitic bacterium transmitted to humans as well as other vertebrates by the biting of trombiculid mites (chigger mites). This review explores the strain diversity, biology and pathogenesity of scrub typhus pathogen Orientia tsutsugamushi. Methods: Literature, related to scrub typhus disease and its causative agent Orientia tsutsugamushi was reviewed to extract all the information based on some immunological studies that have been done previously regarding the disease. Result: Orientia tsutsugamushi is a pleiomorphic bacterium and shows very high variability in between its strains such as Karp, Kato, Gilliam, Boryong and Kawasaki. It completes its life cycle within the trombiculid mite (vector) and vertebrate hosts. It causes disease in human and affects the host’s immune system and at present this disease spreads throughout the world and become a major health concern due to its severity and high mortality rate but neglected everywhere due to lack of awareness and there is no vaccine available currently. Conclusion: This study provides the knowledge about genetic and evolutionary relationship of Orientia spp. strains. Understanding the strains diversity and life cycle are crucial for vaccine development as well as sero-diagnostics.