Dengue is a viral disease transmitted to humans through bites from infected mosquitoes. The first global dengue pandemic began in Southeast Asia after World War II. Over the last few decades, the mosquito-borne virus has spread dramatically. Dengue now infects approximately 50 million people each year, killing at least 12 000.

Dengue has become a major international public health concern. More than half of the world’s population lives in at-risk areas. Even more people are likely to be affected as global warming makes mosquitoes more prevalent. Dengue is endemic in more than 100 countries. The most seriously affected areas are in Southeast Asia and the Western Pacific.

Dengue is a flu-like illness that causes severe joint pain. Complications from dengue can be fatal. In a small number of cases, the disease progresses to dengue hemorrhagic fever (DHF), leading to hemorrhage, shock and possibly death. Whether a patient develops DHF will depend on the strain of the infecting virus and the patient’s age, immune status and genetic predisposition.

There are four main types of closely related viruses that cause dengue. A person infected with one virus type, however, does not become immune to the other three. In fact, with every new infection, the disease gets worse. Repeated infections increase the risk of the disease progressing to dengue hemorrhagic fever (DHF), a potentially fatal complication.

Dengue viruses are transmitted to humans through the bites of infected Aedes aegypti mosquitoes. The mosquito acquires the virus when it feeds on the blood of an infected person. It can then transmit the virus to other humans every time it bites. Factors contributing to the spread of dengue include:

• Substandard housing, inadequate water and sewer systems, which foster mosquito breeding;
• Uncontrolled urbanization and population growth;
• Increased air travel, which can transport dengue-carrying mosquitoes.;

For more than 200 years, dengue was considered to be a benign fever. The disease was confined to relatively small geographic regions and the four different types of viruses remained isolated. Dengue outbreaks did occur, yet rarely progressed to the more deadly dengue hemorrhagic fever (DHF). Today, as the number of epidemics caused by multiple virus types grows, each outbreak becomes more vicious. Before 1970, only nine countries had experienced DHF epidemics. By 1995, that number had increased four-fold.

There is a small but significant risk of dengue outbreaks in the United States. Each year, people returning from tropical areas import the viruses. Southern Texas and the southeast US, where mosquitoes that spread dengue are found, are at risk of a dengue outbreak.

There are approximately 500 000 cases of DHF a year that are severe enough to require hospitalization. As many as 5 percent of DHF cases are fatal – a very large proportion are children. Without proper treatment, fatalities can rise to 20 percent.

There are no effective treatments for dengue infection. Currently, the only way to control or prevent dengue is to kill mosquitoes.

The mosquito that spreads dengue, Aedes aegypti, does not need much water to breed. The larvae are often found in household water storage jars, buckets and plastic containers that collect rainwater. The International trade in used tires is a concern because rainwater collects in used tires, creating a perfect mosquito breeding ground. This has helped another dengue vector spread rapidly to the US, Latin American and Caribbean countries.

The mosquito is eradicated through environmental management and pesticide spraying. Community-based programs that encourage proper solid waste disposal and improve water storage practices are effective. Pesticide spraying is an emergency measure used during outbreaks. It is only partially effective because the aerosol droplets rarely penetrate indoors where adult mosquitoes survive.

Researchers have attempted to develop a vaccine for 20 years with little success. The difficulty is that an effective vaccine would have to protect against all four dengue viruses. Adding to the complication: if one part of the four “arms” of the vaccine fail, those vaccinated would be at a greater risk for dengue hemorrhagic fever (DHF) than those who did not receive the vaccine. Because of this, NITD plans to concentrate its efforts on developing antiviral compounds. Administering antivirals in particular areas at the first indication of an outbreak will be more cost-effective than mass inoculations.

Work on antivirals for dengue is still at a very early stage. Researchers at NITD are encouraged by the success of antiviral compounds, such as protease inhibitors, in treating HIV. It will, however, take a huge amount of work and commitment to reduce the toll from dengue and bring treatments to people who desperately need them.