Study on the Behavior of Dengue Viruses during Outbreaks with Reference to Entomological and Laboratory Surveillance in the Cuddalore, Nagapattinam, and Tirunelveli Districts of Tamil Nadu, India

OBJECTIVES This study was carried out in order to understand the behavior of dengue viruses through the entomological and laboratory surveillance of outbreaks. The aim of the study was to provide additional research to support current knowledge of epidemiological, clinical, and laboratory diagnosis of dengue virus and ultimately to use this information to forecast dengue as well as to justify intervention measures. METHODS Data on the presence of Aedes larvae in human dwellings during the entomological surveillance in Cuddalore, Nagapattinam, and Tirunelveli dengue outbreaks were taken to compute indices, namely the House Index (HI), Container index (CI), and the Breteau Index (BI). Standard procedures were followed for nonstructural Protein 1 (NS1) and immunoglobulin M enzyme linked immunosorbent assay for the confirmation of dengue. Serovar confirmation was made in the Kottayam field station of the Vector Control Research Center, Puducherry. RESULTS Larval indices HI < 2-3% and BI < 20 contributed to halting the outbreak. Incubation of the dengue viruses in humans was detected at 15 days, NS1 was identified as a tool for the early diagnosis of dengue cases and its presence indicated the need to implement all available interventions. It was also discovered that it is helpful to search for hidden habitats of Aedes when dengue cases have not been reduced even after the sustainable management of the larval indices, HI < 5% and BI < 20. Based on the observed incidences of stopping dengue outbreaks, it was learnt that neighborhood areas of the outbreak villages, around 400 m, should have permissible larval indices < 5% HI and BI < 20. Heterogeneous serovars that led to dengue hemorrhagic fever and Dengue Shock Syndrome (DSS) were identified using reverse transcription polymerase chain reaction and reconfirmed in the field as DEN-1 and DEN-3 viruses and were circulating in Tirunelveli during the outbreak. CONCLUSION The behaviors of dengue viruses experienced in experimental, clinical, epidemiological, entomological, and laboratory surveillance did not deviate from observations in the field during dengue outbreaks in the Cuddalore, Nagapattinam, and Tirunelveli districts of Tamil Nadu, India.