Occurrence of Orientia Tsutsugamushi Genotypes in Areas of Union Territory of Puducherry and Tamil Nadu State, India

Abstract

Scrub typhus, caused by the proteobacterium, Orientia tsutsugamushi, is re-emerging in several regions of Asia, particularly in India. Severity of infection and clinical presentations are known to vary with the infecting prototype/ genotype. Hence genotypic characterization and distribution of various genotypes is of clinical and epidemiological importance. One hundred and forty five suspected scrub typhus cases, reporting to a tertiary care centre in Puducherry, India were investigated for O. tsutsugamushi specific IgM antibodies by ELISA out of which, 135 (93%) were positive. Most cases occurred post-monsoon, peaking in September, and there was a preponderance in young adults. Forty samples tested positive by Nested PCR based on 56kDa gene of O. tsutsugamushi and amplicons from PCR positive samples were sequenced. Phylogenetic tree constructed using 35 sequences (from nt 20 to nt 130) obtained in the study, along with those retrieved from NCBI site, formed two major branches; one comprising 15 sequences from this study, which aligned with Karp genotype, and the other containing 6 sequences which aligned with a sequence from Vellore, India. The second major branch had 12 sequences, which formed an independent group from the Gilliam prototype. Analysis of association of clinical manifestations with genotypes obtained in the present study showed that the sequences that formed an independent group, were associated with a wide spectrum of clinical manifestations involving multiple organs and more severe manifestations like ARDS and hypotension. The sequences, which branched with Karp prototype were associated with hepatitis, meningitis and Multi-organ disorder syndrome (MODS). The present study thus indicated that different genotypes of O. tsutsugamushi occur in southern regions of India, which were associated with various clinical manifestations. Studies on the occurrence of genotypes will help in development of diagnostic methods and vaccines to curtail the infection.

Clinical, laboratory, and molecular epidemiology of Orientia tsutsugamushi infection from Southwestern India

“…In patients from Puducherry and Tamil Nadu, India, isolates close to Vellore were causing less severe infection with a narrow spectrum of infection and isolates close to Taiwan were causing much severe infection with multi-organ involvement including ARDS and hypotension. Karp was associated with hepatitis, meningitis and multiorgan dysfunction syndrome [ 21 ]. In contrast, Karp infected patients in our study had respiratory and cardiovascular involvement followed by severe thrombocytopenia.…”

“…Neimeng-65 isolates reported from Shillong [7], were not seen in our study. Pathogen factors and strain variations leading to varying clinical presentation, organ involvement and outcome have been discussed in various in vivo and clinical studies [21][22][23][24]. In BALB/c mice, Karp was found to be lethal, while mice induced with Kuroki strains survived [24].…”