Vector and rodent surveillance for Orientia tsutsugamushi in north India

Background & objectives: Scrub typhus or chigger borne typhus, caused by Orientia tsutsugamushi is an emerging vector-borne disease as large numbers of cases have been reported in various tropical countries. It is transmitted to humans through bites of infected chiggers (larval mites). The knowledge about the vector, its distribution, density and habitat are important so as to understand the epidemiology of scrub typhus in a given area. To control rickettsial infections, regular rodent-vector surveillance should be planned in areas where the disease transmission is occurring and it will also help to strengthen the existing entomological data related to the vector of scrub typhus in northern India. Methods: In the present study, rodent-vector surveillance was planned for one whole year, covering both mite active and non-active seasons (October 2019–December 2020) in selected areas of Chandigarh and Punjab in north India. Rodent tissues and mites were also examined for the presence of O. tsutsugamushi by nested PCR for 56 kDa gene and real-time PCR for 47 kDa outer membrane protein gene. 18S gene PCR was performed for molecular identification of mites. Results: In the surveillance, three types of ectoparasite, viz. mites, fleas and ticks were obtained in rodents. All mites found were of Laelapidae family. None of the pooled rodent tissue samples as well as mite samples were found positive for O. tsutsugamushi by nested PCR for rickettsial DNA. Interpretation & conclusion: In the present study, we did not get any evidence of carriage of O. tsutsugamushi in either mites or rodents collected and sampled in selected regions in Chandigarh and Punjab. We need to strengthen the entomological surveillance over a broader region and increase the frequency of trapping rodents to increase clarity on vector-reservoir dynamics in this geographical region.

Scrub typhus: a hospital-based study in the northern districts of West Bengal, India

Background: Scrub typhus caused by Orientia tsutsugamushi, is a mite-borne zoonotic acute febrile illness. Geographically, it is confined to the Asia-Pacific region and important re-emerging infection in India. Clinical diagnosis of scrub typhus from other acute febrile illness is very difficult due to nonspecific symptoms and the relative absence of eschar in the Indian population. Case fatality rate varies from 30-70% depending on the clinical suspicion, delay in diagnosis and treatment. Antibody-based serological tests are the mainstay of diagnosis. IgM enzyme-linked immunosorbent assay (ELISA) against O. tsutsugamushi is helpful for the diagnosis of scrub typhus within the first week of illness.Methods: The aim of the study was to determine the prevalence of the disease in Northern districts of West Bengal, India using IgM ELISA.Results: Out of 577 serum samples tested 10.05% were positive for IgM antibodies. Majority of cases were below 40 years of age with higher prevalence in female patients. The disease showed a seasonal trend with a peak during the monsoon and later months. The case fatality rate among ELISA positive cases was 32.76%.Conclusions: Significant seropositivity against scrub typhus among cases of acute febrile illness with relatively higher mortality indicates that scrub typhus should be included in the differential diagnosis and confirmed by IgM ELISA.

Cleavage of p65 Subunit of NF-kappaB by Orientia tsutsugamushi

Orientia tsutsugamushi, a causative agent of scrub typhus, is an obligate intracellular parasite and usually propagates in the cytoplasm of host endothelial cells and macrophages. Macrophages are the first defense line against bacterial infection and NF-kappaB is activated upon contact with bacteria, resulting in the transcription of inflammatory cytokine to control bacterial infection. In this study, we investigated whether O. tsutsugamushi modulates NF-kappaB activation in the macrophages. We examined the changes of NF-kappaB proteins upon infection with O. tsutsugamushi and found that NF-kappaB is activated at a slow rate as judged with EMSA and immunoblot analysis. Interestingly, we found that p65 was cleaved generating a 45 kDa fragment. In addition, fragment of p65 is generated only by the virulent serotype strain of O. tsutsugamushi, suggesting this cleavage may be associated with the mouse virulence. It is still unknown whether this is a direct result of O. tsutsugamushi proteins or enzymes of host cell. Further exploration of the mechanism that modulates NF-kappaB activity by O. tsutsugamushi could contribute to a better understanding of the molecular pathogenesis of O. tsutsugamushi infection.