While research is underway on developing a vaccine to protect against dengue, this presents a challenge because any effective vaccine would have to offer immunization against all four types to be effective - and there is still a limited understanding of how the disease typically behaves and how the virus interacts with the immune system.
There are also few laboratory animal models available to test immune responses to potential vaccines - but nevertheless two vaccine candidates have already advanced to evaluation in human subjects in countries with endemic disease, and several potential vaccines are in the earlier stages of development - however an effective dengue vaccine for public use will not be available for 5 to 10 years.
There are several reasons for the dramatic global emergence of Dengue fever and Dengue haemorrhagic fever as a major public health problem but they are complex and not well understood.
Several important factors have been identified - major global demographic changes have occurred resulting in uncontrolled urbanization and concurrent population growth, often accompanied by substandard housing and inadequate water, sewer, and waste management systems, all of which increase mosquito populations and facilitates the transmission of mosquito-borne diseases.
Also in most countries public health infrastructures have deteriorated and limited financial and human resources and competing priorities have resulted in a "crisis mentality" with an emphasis on implementing so-called emergency control methods in response to epidemics, rather than developing programs to prevent epidemic transmission.
This approach has been particularly detrimental to dengue control because, in most countries, surveillance is, as in the U.S., is passive and the systems used to detect increased transmission normally relies on reports by local doctors who often do not consider Dengue in their differential diagnoses and as a result, an epidemic has often reached or passed its peak before it is recognized.
Increased travel by airplane also provides the ideal mechanism for infected human transport of Dengue viruses between population centers of the tropics, resulting in a frequent exchange of Dengue viruses and other pathogens.
In addition effective mosquito control is virtually nonexistent in most Dengue-endemic countries and the outlook for reversing the recent trend of increased epidemic activity and geographic expansion of dengue, is not promising.
Experts say new Dengue virus strains and serotypes are likely to continue to be introduced into many areas where the mosquito population is high and no new mosquito control technology available.
Despite public health authorities in many countries emphasizing disease prevention and mosquito control through community efforts to reduce larval breeding sources, this approach will probably only be effective in the long term and is unlikely to impact disease transmission in the near future.
Disease experts believe improved, proactive, laboratory-based surveillance systems must be developed to provide early warning of an impending Dengue epidemic to allow the public to take action and doctors to diagnose and properly treat Dengue and Dengue haemorrhagic fever cases.
The threat to public health posed by Dengue, has been recognized by the National Institute of Allergy and Infectious diseases (NIAID) which is funding nearly 60 Dengue research projects, including studies on Dengue haemorrhagic fever and Dengue shock syndrome, the most severe forms of the disease.
NIAID research priorities include effective community-based prevention programs; improved laboratory-based international surveillance; rapid diagnostic tests and therapies; and the development of and clinical trials for Dengue vaccines
According to the WHO the Aedes albopictus mosquito, a secondary Dengue vector in Asia, has now become established in the United States, several Latin American and Caribbean countries, parts of Europe and Africa, largely attributed to the international trade in used tyres, a known breeding habitat.
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