The options available for prevention and control of DEN/DHF are limited. Although currently not available, considerable progress has been made in recent years in development of a vaccine for dengue/ DHF. Effective vaccination to prevent DHF will require a tetravalent, live attenuated vaccine. Promising candidate attenuated vaccine viruses have been developed and have been evaluated in phase I and II trials in Thailand. A commercialization contract has been signed and the tetravalent vaccine formulation is currently undergoing repeat phase I and II trials.
Promising progress has also been made on developing second-generation, recombinant dengue vaccines by using cDNA infectious clone technology. An infectious clone of the DEN-2, PDK-53 vaccine candidate virus has been constructed, and work is currently in progress to construct chimeric viruses by inserting the capsid, premembrane (PrM) and envelope genes of DEN-1, DEN-3 and DEN-4 into the DEN-2 PDK-53 backbone. These recombinants, through genetic manipulation, may be made to grow better, be more immunogenic and safer.
The development of other new technology such as DNA vaccines is in its infancy. Despite the promising progress, it is unlikely that an effective, safe and economical dengue vaccine will be available in the near future. It will likely be 10 or more years before an effective, safe, economical vaccine is commercially available. Currently, the only way to prevent dengue infection is to control the mosquito vector that transmits the virus.
Unfortunately, our ability to control Ae. aegypti is limited. For over 25 years, the recommended method of control was the use of ultra low volume (ULV) application of insecticides to kill adult mosquitoes. Field trials in Puerto Rico, Jamaica and Venezuela, however, showed that this method was not effective in significantly reducing natural mosquito populations for any length of time. This supports epidemiologic observations that ULV has little or no impact on epidemic transmission of dengue viruses.
The only truly effective method of controlling Ae. aegypti is source reduction, that is to eliminate or control the larval habitats where the mosquitoes lay their eggs. Most important larval habitats are found in the domestic environment, where most transmission occurs. To have sustainability of prevention and control programs, some responsibility for mosquito control must be transferred from government to citizen homeowners. Mosquito control programs, therefore, must be community-based and integrated. Persons living in Ae. aegypti infested communities must be educated to accept responsibility for their own health destiny by helping government agencies control the vector mosquitoes, and thus prevent epidemic dengue/DHF/DSS.
Countries with endemic dengue should develop active, laboratory-based surveillance systems that can provide some degree of epidemic prediction. Finally, prevention of excess mortality associated with DHF/ DSS can be achieved by educating physicians in endemic areas on clinical diagnosis and management of DHF/DSS. As demonstrated in countries such as Thailand, early recognition and proper management are the key to keeping DHF/DSS fatality rates low.
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