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The plankton and semi-plankton samples collected from four floodplain lakes (beels) of Barpeta district of lower Brahmaputra river basin, Assam state, northeastern India (NEI) revealed eighteen rotifer species of biodiversity and biogeographic interest belonging to five families and six genera. One species is new to the Indian Rotifera and one species is new to Assam. Our collections are characterized by two Australasian elements, five Oriental endemics, seven paleotropical species, and one cosmo (sub) tropical species. Nine species, restricted to date to NEI, are examples of regional distribution importance in India while six species depicted disjunct distribution in the country. Interestingly, seven species are categorized as Eastern hemisphere elements. All the taxa are illustrated to warrant validation as an increasing magnitude of 'unverifiable records' is a serious impediment for the progress of rotifer biodiversity in India. [ABSTRACT FROM AUTHOR]

Background: In India, scrub typhus (ST) is considered to be a reemerging infectious disease. From northeast India, ST cases have recently been reported (2012) in Assam after a gap of 68 years. The causative organism, Orientia tsutsugamushi is known to be genetically and antigenically highly variable. Sequence analysis of 56-kilodalton (kda) type-specific antigen (TSA) gene has become an important tool for genetic characterization of Orientia. This variable gene sequence is useful for analysis of genetic diversity of Orientia isolates. Although re-emergence of ST has been reported, circulating strains and their origin have yet to be identified. In the present study, we determined the prevalent strains of O. tsutsugamushi circulating in Assam and their origin with respect to 56 kDa TSA gene. Methods & Materials: 370 clinical serum samples from suspected scrub typhus and other unidentified fever cases were received from tertiary hospitals in Assam. Serological screeningwas done using Scrub Typhus Detect IgM ELISA (InBios International, Inc., USA). Positive and equivocal samples were subjected to PCR. Nested PCR was performed using primers specific for O. tsutsugamushi 56 kDa gene. Phylogenetic analysis was performed using MEGA 6 software. Results: 19.4% sera (72/370) were found to be IgM positive and 6.4% (24/370) were equivocal. 13 of these samples were PCR positive for 56 kDa gene. Phylogenetic analysis of study strains showed variations in sequence homologies that formed 3 distinct clades that clustered with reference strains from: 1) India 2) Taiwan and 3) Thailand. Conclusion: In summary, we have identified strains of O. tsutsugamushi circulating in Assam and established their evolutionary relationship with reference strains by analyzing a variable portion of 56 kDa gene. Understanding the evolution of the prevalent strains is important to understand the genetic differences which may help in planning control strategies as well as prophylactic measures including development of vaccines. [ABSTRACT FROM AUTHOR]