WHO takes aim at dengue in strategy document

Sep 4, 2012 (CIDRAP News) – Saying dengue virus infections and deaths have mushroomed in recent years, the World Health Organization (WHO) recently released a strategy report that sets a goal of cutting deaths in half and reducing cases by 25% over the next 8 years.

The report, titled Global Strategy for Dengue Prevention and Control, also sets a goal of estimating the true burden of dengue disease by 2015—signaling how little is known about the global impact of the mosquito-borne illness.

"Compared with the situation 50 years ago, the worldwide incidence of dengue has risen 30-fold," WHO Director-General Margaret Chan, MD, MPH, wrote in a foreword to the report. "More countries are reporting their first outbreaks. More outbreaks are explosive in ways that severely disrupt societies and drain economies.

"Today, dengue ranks as the most important mosquito-borne viral disease in the world. Everywhere the human and economic costs are staggering."

The WHO estimates that 50 million to 100 million dengue cases occur annually and that almost half the world's population lives in countries in which the disease is endemic. Close to 75% of people exposed to dengue live in the Asia-Pacific region.

Severe dengue cases number in the hundreds of thousands each year, and about 20,000 of them are fatal, according to estimates cited in the report. "The true numbers are probably far worse, since severe underreporting and misclassification of dengue cases have been documented," it adds. Brazil has been among the countries particularly hard hit.

Given the impact of dengue, an international effort to control it is long overdue, the WHO says, adding, "New opportunities to overcome the disease now make such an effort feasible." Moreover, because the International Health Regulations list dengue among the diseases that may cause a public health emergency of international concern, governments should act to build defenses against it, the agency says.

In general, the report says that the tools already exist to make a big dent in the dengue problem, but that better tools, particularly in the diagnostic realm, are urgently needed. Currently there is no licensed vaccine or specific treatment for dengue fever or its more serious complication, dengue hemorrhagic fever.

"Despite the complex clinical manifestations of this disease, its management is relatively simple, inexpensive and highly effective in saving lives, provided correct and timely interventions are instituted," Chan wrote.

The report asserts that dengue deaths can be nearly eliminated through timely, appropriate clinical management, "which involves early clinical and laboratory diagnosis, intravenous rehydration, staff training and hospital reorganization." It adds, "Research to provide better diagnostics and biomarkers to predict disease severity are urgently needed."

The key to proper treatment is early recognition and understanding of the problems that arise during the three phases of the disease: febrile, critical, and recovery, according to the report.

The broad strategy the report describes for reducing the number of dengue cases includes (1) using coordinated epidemiologic and entomological surveillance to better predict and detect outbreaks and (2) promoting integrated mosquito management and using locally adapted mosquito-control measures, including effective urban and household water management

There are historical examples of the elimination or significant reduction of both yellow fever and dengue through control of Aedes aegypti mosquitoes, the primary dengue vector, the report notes. Recently, it says, Singapore and Cuba greatly reduced dengue transmission by passing "anti-Aedes legislation" and taking sustained action to control mosquitoes.

The WHO says some of the newer mosquito-control tools could play a role in the long-term strategies of nations, but it doesn't single out any one technology. It mentions insecticide-treated materials, lethal egg traps, spatial repellents, genetically modified mosquitoes, and A aegypti infected with the bacterial parasite Wolbachia.

As for a dengue vaccine, the report says one could become available within 2 to 4 years, even though "proof of concept of vaccine efficacy" is still lacking. "Challenges to vaccine development include the need to provide protection against all four dengue viruses, as well as resolving questions about the immune correlates of protection," it states.

The most advanced vaccine candidate, which uses a live attenuated hybrid of yellow fever and dengue viruses, is in phase 3 clinical trials, the report notes. Other vaccines in clinical development include several live attenuated vaccines, a subunit vaccine, and a DNA vaccine.

When a vaccine does become available, dengue-endemic countries will face a number of questions about how to use it, such as which groups to target for vaccination; how to deliver the vaccine, which may require multiple doses; how to monitor its safety and effectiveness; and determining the role of vector control, surveillance, and case management in enhancing the impact of the vaccine, the WHO says.

"Current dengue prevention and control strategies should include vaccines as an important element to anticipate and prepare for," the report states. "This includes preparing for future decision-making on vaccine introduction and use, considering the integration of vaccines with other tools for dengue prevention and control, and investments in surveillance systems and safety monitoring of vaccines."

The report also includes a chapter on "enabling factors" for the dengue strategy, including advocacy and resource mobilization, coordination and collaboration, communication to achieve behavioral outcomes, local capacity building, and monitoring and evaluation.

See also:

Full text of report (43 pages)

Jan 24 CIDRAP News story "WHO says 40% of population at risk for dengue fever"

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