Genotype shift of dengue virus (DENV1) during the 2017 outbreak of dengue fever in Thiruvananthapuram, Kerala, India

961-966An unprecedented outbreak of dengue occurred during 2017 in Kerala. Thiruvananthapuram was worst affected. We carried out a joint investigation with the Health department of the State, to understand the epidemiological and entomological factors involved in this outbreak, so as to develop strategies to contain it. Blood samples from suspected patients were collected from three worst affected areas and genomic analysis of the Dengue virus (DENV) was performed. Also, a cross sectional entomological survey was carried out in these areas. The data obtained was compared with the available secondary data of DENV in Kerala. The investigations revealed a genetic shift from the erstwhile predominant DENV2/DENV3 serotypes to the newly introduced DENV1 Asian genotype during the current outbreak. Breeding indices of Aedes aegypti, the predominant vector species was also found to be remarkably high. Asian genotype of DENV1 was detected in field collected Ae. aegypti also. The index cases of the Asian genotype of DENV1 in Kerala were detected from Erumeli village (gateway to the famous Sabarimala shrine) among two plantation workers migrated from the neighbouring Karnataka state, during 2013. This introduced virus strain attained an epidemic proportion in 2017 in Thiruvananthapuram, owing to immunologically naïve population and high receptivity