Emergence of Dengue Problem in India ? A Public Health Challenge

India contains approximately half of the 205 billion people worldwide who are at risk of dengue fever. The virus causing Dengue/ DHF is believed to have established in almost all parts of India and has emerged as a major public health concern. Dengue is found in tropical and sub- tropical regions around the world, predominantly in urban and semi- urban areas. It is the most common mosquito- borne viral disease of humans. Globally, 2.5 billion people live in areas where dengue viruses can be transmitted. Aedes aegypti is the main vector playing a major role in the transmission of dengue/ DHF. Dengue fever and its severe complication i.e. DHF are caused by one of four types of distinct, but closely related, viruses namely DEN1, DEN2, DEN3 and DEN4 of genus flavivirus. By the last decade of the 20th century, Aedes aegypti and the four dengue viruses had spread to nearly all the countries of the tropical world. Some 2 billion persons live in dengue- endemic areas with tens of millions infected annually. Dengue pandemics were also documented in the 18th and 19th centuries; they were contained by organized anti- Aedes aegypti campaigns and urban improvements. The 20th century dengue pandemic has brought with it the simultaneous circulation of multiple serotypes and in its aftermath, endemic dengue haemorrhagic fever/ dengue shock syndrome (DHF/ DSS). At the national level, dengue control is coordinated by the National Vector Borne Diseases Control Programme (NVBDCP). NVBDCP is the agency responsible for framing national dengue guidelines and policies for guiding the implementations of programme strategies at the state level. In the absence of a vaccine, vector control is the main strategy to prevent dengue outbreaks. The country paradigm for dengue control is largely passive surveillance and early case detection coupled with rapid mobilization in the case of an outbreak. The first outbreak of DHF occurred in Calcutta in 1963. After that disease outbreaks reported from different states. The first major outbreak of dengue fever (DF) was reported in Calcutta in 1963. Since then, more than 60 outbreaks have been reported in India from different states. During recent years, it has become a major public health problem in the urban areas of India and is gradually spreading to the rural areas. The problem of dengue is increasingly becoming important in most tropical countries due to the expanding urban areas, limited piped water supply, constant influx of people from rural to urban areas, creation of slums, and high rise buildings with increased use of water coolers during the summer season. An epidemic of dengue was also reported in Rajasthan in 1985. A severe outbreak of dengue was reported in 1996 in Delhi with more than 400 deaths. Gurgaon town of Haryana state faced similar outbreak of dengue with 1137 cases and 9 deaths in 2008. During 2009, Pune Corporation in Maharashtra state reported an outbreak of dengue. The state reported 2255 cases and 20 deaths. The maximum dengue deaths were reported from Haryana, Kerala, and Punjab state. Aedes aegypti was the only vector in all these outbreaks. The epidemic, which occurred during 2005- 06 in certain islands of Indian Ocean and in Kerala strongly suggests that Aedes albopictus played an alternate role. Ae. albopictus invaded the peridomestic settings, hitherto the exclusive domain of Ae. aegypti. The aggressive nature of Aedes albopictus, when compared that of to Ae. Aegypti, may help them to out compete the latter and could play a crucial role in the disease transmission due to aggressive bites in Kerala state. Ae. albopictus, a secondary vector for dengue, is likely a significant factor in the persistence of dengue in the environment through vertical transmission and may be replacing Ae. aegypti in semi- urban areas.