Molecular investigations of dengue virus during outbreaks in Orissa state, Eastern India from 2010 to 2011

Dengue is one of the most important arboviral diseases in India. Orissa state in Eastern India reported the first dengue outbreak in 2010, followed by extensive outbreaks in 2011, affecting large number of people. Detailed entomological, serological and phylogenetic investigations were performed in mosquitoes and patients serum collected from dengue virus (DENV) affected areas of Orissa. The combination of DENV specific IgM capture-ELISA and reverse-transcription PCR (RT-PCR) detected high DENV positivity in serum samples. DENV was detected in mosquitoes reared from field caught pupae by RT-PCR, which confirmed the vertical transmission of DENV that may have an important role in the recurrence of dengue outbreaks. Phylogenetic analyses revealed the circulation of Indian lineage of DENV-2 (genotype-IV) and DENV-3 (genotype-III) in vectors and patients serum in Orissa from 2010 to 2011, DENV-2 being the prevailing serotype. Selection analyses within the C-prM region showed that the emergence of DENV-2 and DENV-3 in Orissa was constrained by purifying selection which suggested the role of ecological factors like mosquito density and behavior in the recurrent outbreaks. Aedes albopictus was found to be the most abundant vector in the areas surveyed, followed by Aedes aegypti. Indoor breeding spots (earthen pots) were most abundant, with high pupal productivity (38.50) and contributed maximum Aedes species in the affected areas. The DENV infection rate estimated by maximum likelihood estimate (MLE) was high for indoor breeding Aedes (4.87; 95% CI: 1.82, 10.78) in comparison to outdoor breeding Aedes (1.55; 95% CI: 0.09, 7.55). The high MLE in Ae. albopictus (4.72; 95% CI: 1.94, 9.80) in comparison to Ae. aegypti (1.55; 95% CI: 0.09, 7.54) indicated that Ae. albopictus was the main DENV vector responsible for the outbreaks. The results indicated the circulation of two virulent serotypes of DENV in Orissa, mainly by Ae. albopictus with the implication for implementation of intradomecile vector control measures to prevent the spread of dengue.