|Dengue and Dengue Haemorrhagic Fever: Surveillance, Prevention and Control (WHO, 3 p.)|
The resurgence of dengue fever, and the emergence of dengue haemorrhagic fever (DHF) as major public health problems, are rooted in the demographic trends and socio-economic policies of the 20th Century. The population of the world has doubled in the last 27 years, accelerating most rapidly in the developing countries of the tropics and sub-tropics where this viral disease is spread by mosquitoes. Population growth, rural-urban migration, inadequacy of basic urban infrastructure and exponential growth of consumerism, have combined to produce epidemiological conditions that are highly favourable for viral transmission by the main mosquito vector, Aedes aegypti. This species thrives in intimate association with humans and is also the vector of epidemic yellow fever, a vaccine-preventable disease.
World Urbanization Trends, 1950-2030
Source: United Nations. World Urbanization Prospects (The 1996 Revision).
THE GENERAL DISTRIBUTION DENGUE AND/OR DENGUE HAEMORRHAGIC FEVER, 1975-1999
Rapid increase in dengue haemorrhagic fever
Forty percent of the worlds population is now at risk from dengue but only a small proportion of cases are officially reported to WHO. Nevertheless, 1998 witnessed unprecedented levels of reporting, with approximately 1.2 million cases from 56 countries. However, an estimated 50 million infections occur annually, including 500,000 cases of DHF and dengue shock syndrome, with 24,000 deaths, mostly in children.
Before 1970 only nine countries had experienced DHF epidemics, a number which has since increased more than four-fold. Today, in several Asian countries DHF is a leading cause of paediatric hospitalisation and death. There is no specific cure and a vaccine is not available. However, the adoption of appropriate, standardized clinical management practices can effectively reduce DHF case fatality rates.
Recent calculations of the global burden of disease indicate that the combined losses attributable to dengue and DHF are much greater than previously indicated. For example, the economic impact of dengue and DHF per million population in Puerto Rico is estimated to be similar to that of all of Latin American and the Caribbean for malaria, for hepatitis and for meningitis. The magnitude of the public health problem will continue to grow unless more effective measures are taken to reduce transmission. Currently the only available control measures are aimed at reduction of the mosquito vector population.
The goal of WHO is to reduce the global burden of disease attributable to dengue and DHF. The Organizations role is to provide technical support and guidance to Member States in planning, implementing and evaluating prevention and control measures.
The global strategy for prevention and control of dengue/DHF provides the basis for national programme planning. Essential elements are integrated mosquito control with community and intersectoral involvement, disease and vector surveillance for monitoring and evaluation, emergency preparedness, capacity building and training, and applied research. Future prospects for the availability of a vaccine that affords protection against all four dengue serotypes offers the promise of an additional intervention to combat the disease among high risk groups.
The medium-term priorities (four to six years), identified in October 1999 by a WHO consultation which reviewed the global strategy, are along three major paths:
· Strengthening surveillance for planning and response, including entomological surveillance and the monitoring of key human behaviours such as those which contribute to the availability of mosquito larval habitats. Epidemiological surveillance includes the introduction of DengueNet, a global surveillance system for dengue fever on the internet. This database will be continually updated and will allow remote entry to provide a more comprehensive and current global picture.
· Reducing the disease burden through accelerated training and adoption of WHO standard clinical management guidelines for DHF; and improving emergency preparedness and response;
· Changing behaviours, through development of a package of tools, approaches and guidelines for sustainable prevention and control that will address the problem at the individual, household, community, institutional and political levels as well as foster intra - and inter-sectoral partnerships for programme implementation.