Dengue Hemorrhagic Fever and Dengue Shock Syndrome

The Dengue virus is an arbovirus, from genus Flavivirus family Flaviviridae. It is a single stranded RNA genome surrounded by an icosahedral nucleocapsid and covered by lipid envelope. Four serotypes: DEN-1, 2, 3, 4 have been identified for the virus. Each serotype provides specific lifetime immunity, but only a shortterm cross-immunity. All serotypes can cause severe and fatal disease. In the epidemic in Delhi in 2003, Guate9698 strains of DEN-3 virus were held responsible for the outbreak1. The vector for Dengue is the Aedes aegypti mosquito which is also known as the Tiger mosquito, due to the characteristic striped body appearance. It is a highly domesticated mosquito and lays eggs and produces larvae preferentially in artificial containers. Two peaks of biting activity are known for the mosquito – 2-3 hours after the daybreak and in the evening a couple of hours before sundown. The mosquito is a silent and fearless biter and does not buzz. It often feeds on several persons during a single blood meal in a short period of time. If infective, it can transmit the virus even while probing without taking blood meal1. Epidemics of an illness resembling dengue have been known to have occurred in 1779, 1780 across three continents of Asia, Africa and North America. The first epidemic of DHF in recent times occurred in Manila, Philippines 1953. In India dengue virus was first isolated in Calcutta in 1945 and the epidemic of DHF first occurred in Calcutta in 1963. Since then epidemics of dengue fever have been reported from Vishakhapatnam, Ajmer, Delhi and Kanpur, mostly attributed to strains DEN 2 and DEN 3. In the recent epidemic Dengue and Chikungunya fever cases were reported from 182 districts in Haryana, Delhi, Rajasthan, Gujarat, Maharashtra, Karnataka, Kerala, West Bengal, Madhya Pradesh, Andhra Pradesh, Tamil Nadu, Pondicherry, Andaman and Nicobar islands. As many as 2300 patients were diagnosed for Dengue Fever in Delhi alone and more than 50 deaths were reported.