Distribution and Incidence

Dengue literally girdles the globe, with a distribution approximately equal to that of its principal vector, A. aegypti. Areas of dengue endemicity include tropical and subtropical regions of the Americas, Africa, Asia, and Australia. There are areas of A. aegypti infestation in Europe and in the southern United States, where dengue has caused epidemics in the fairly distant past, but which have no current dengue activity although they remain susceptible to its reintroduction. The example of the 1927-8 outbreak of dengue in Athens and adjacent areas of Greece illustrates such a situation, for, although type 1 dengue virus caused an epidemic with a high incidence of hemorrhagic manifestations and a high death rate in the region, that region today is not considered to be one of significant dengue prevalence.

Types 1, 2, 3, and 4 dengue viruses are endemic in Asia. Types 1, 2, and 3 are prevalent in Africa, where type 3 is the most recent arrival, first identified in Mozambique during the 1984-5 epidemic. Types 1, 2, 3, and 4 are now present in the Americas, where type 1 made its first appearance in 1977; in the Caribbean, type 4 appeared in the same region in 1981. Type 1 dengue virus was found to be responsible for the 1981—2 Australia epidemic in northern Queensland.

Dengue fever epidemics typically involve large numbers of people and have a high attack rate. As many as 75 percent of the susceptible persons exposed to dengue virus will acquire the disease. Mosquitoes take between 8 and 11 days to become infectious after ingesting infected blood, and remain infectious for life; therefore, a single mosquito can infect a number of members of a household. The 1977 Puerto Rican dengue epidemic resulted in the infection of an estimated 355,000 persons with types 1, 2, and 3 virus; the 1986 Rio de Janeiro type 1 epidemic affected 100,00 persons between March and May alone.

Recurrent outbreaks of dengue in the same geographic region indicate either that new dengue virus types have been introduced or that endemic types are now affecting groups of the population lacking immunity - generally those born since the last epidemic.

Dengue hemorrhagic fever is especially frequent in Southeast Asia, where it is among the leading causes of hospital admissions in children and the commonest cause of death from communicable disease at any age. Dengue hemorrhagic fever's first reported appearance in epidemic form in the Western Hemisphere came during the 1981 Cuban epidemic. Several cases of dengue hemorrhagic fever with shock and death were reported during the 1984-5 Mozambique epidemic. Review of data from the 1897 epidemic of dengue in north Queensland suggests that the deaths of 30 children were the result of dengue shock syndrome.

A. aegypti is primarily a domestic mosquito, breeding around areas of human habitation in discarded tires, cans, and other containers that can act as receptacles for the water necessary for the mosquitoes' breeding places. Worldwide increase in dengue activity appears to be directly related to a failure to control mosquito populations effectively, to overpopulation, to progressive urbanization, and to the social and political disruptions caused by wars. Although a jungle cycle involving forest mosquitoes and wild monkeys, in a fashion similar to that of yellow fever, has been demonstrated, zoonotic acquisition of dengue does not appear to be a factor in the general pattern of increasing dengue prevalence.

The current pattern of dengue epidemiology in the Americas resembles that of Southeast Asia in the 1950s, before it changed from a benign flulike illness to the leading cause of morbidity and mortality in children.

Your Heart and Nutrition

Your Heart and Nutrition

Prevention is better than a cure. Learn how to cherish your heart by taking the necessary means to keep it pumping healthily and steadily through your life.

Get My Free Ebook


Post a comment