Epidemiology - Mosquito-Borne Flaviviruses

Epidemiology

Dengue virus is distributed worldwide. Dengue hemorrhagic fever is primarily a disease of children and a leading cause of death in Southeast Asia.

Geographical distribution: An estimated 3 billion peopleliving in approximately 110 countries worldwide are at a risk of dengue infection. Every year, approximately 100 million people are infected with dengue worldwide. Dengue hemorrhagic fever occurs in approximately 2.51 lakhs of affected persons.

Reservoir, source, and transmission of infection: Humans arereservoirs of the infection. The human host serves as source of viral amplification. Humans are infectious to mosquitoes during viremia for 3–5 days. The infection is transmitted by bite of A. aegypti mosquitoes. After feeding, the virus shows an extrinsic incubation period of 10–14 days in the mosquito, before the mosquito becomes infectious. The mosquitoes are vectors as well as sources of viral amplification. A. aegypti are small and highly domesticated mosquitoes, which breed on artificial water sources, and they prefer to bite humans typically at the back of the neck and at the ankles.

    The initial epidemics of dengue were documented in urban areas, but with recent increase in epidemics of dengue, the con-dition has spread to suburban and rural areas also. Dengue has been spreading from Southeast Asia to the subtropical and tropical Asian countries, Indian subcontinent including India, Sri Lanka, Malaysia, Philippines, New Guinea, Australia, and several pacific islands.

The first epidemic of dengue hemorrhagic fever was described in Manila, Philippines in 1953. Subsequently, dengue hemor-rhagic fever has spread more rapidly with epidemics occurring yearly and major outbreaks occurring every 3 years. Currently, dengue hemorrhagic fever is one of the leading causes of death and hospitalization in children in many Southeast Asian countries.

Unplanned urban development with population explosion and inadequate public health facility, poor vector control, and increased travel to the endemic areas have contributed for spread of dengue worldwide.

Dengue was initially restricted to east coast of India. Subsequently, the virus has affected most parts of India. In India, the first report of dengue included isolation of dengue serotypes 1 and 4 in 1964 followed by serotype 3 in 1968. Since then the reports of dengue have been documented from vari-ous parts of the India including Vellore, Pondicherry, Chennai, Mangalore, Kolkata, Assam, Lucknow, Delhi, and Haryana. The higher incidence of dengue has been reported in children younger than 8 years.

An endemic of dengue was reported between September 2001 and January 2002 in Chennai, Tamil Nadu. Nearly 8000 cases were officially identified. Subsequently, a major outbreak of dengue was observed in western India during October 2002 to December 2003. The dengue etiology was confirmed by viro-logical and serological studies.