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In 2019, Dengue was identified by WHO as one of the top ten threats to global health

Dengue is caused by four closely related viruses (DENV-1, DENV-2, DENV-3 and DENV-4) that belong to the Flaviviridae family. These viruses infect certain species of mosquitoes called Aedes mosquitoes, or Asian Tiger mosquitoes due to the white stripes on their body and legs. Aedes mosquitoes like to live in hot, humid conditions, especially in crowded urban environments where sanitation is poor. They thrive in areas with standing water, open water tanks and containers, and old tires. As a result, dengue is widespread throughout the tropics and sub-tropics, with local variations in risk influenced by rainfall, temperature, relative humidity and the degree of uncontrolled urbanization. 

Almost 4 billion people (approximately 50% of the world’s population) are estimated to live in high-risk areas for dengue and it has been reported from more than 120 countries. However, 70% of the actual burden of disease is in Asia. The total number of dengue cases reported to WHO increased to 4.2 million in 2019, but it is likely that many cases are not diagnosed or reported.

If an Aedes mosquito carrying a dengue virus bites someone, in many cases the person does not develop any signs of illness. Probably only about 25% of human infections cause symptoms and these range from just fever for a few days in some individuals to a nasty flu-like episode in others. 

Occasionally however, a dengue infection can result in severe and potentially fatal illness.

Although no specific treatments are currently available, even people with severe dengue generally recover if they receive expert supportive care. However, this kind of care is very expensive. In addition, although severe complications only happen in a very small proportion of all infections, actual numbers of severe dengue cases are still high in places where millions of infections occur every year. So, the burden on public health services and the economy can be huge in high transmission settings.

How people respond to the bite of an infected mosquito depends on many factors including the amount of virus the mosquito introduces and the ability of the person’s immune system to fight the virus after it enters their body. With many bacteria and viruses, a person’s immune response becomes more effective after repeated exposure to the same bug, so the person is usually less sick with a second or third infection.

Dengue is unusual in that the first infection with any of the four dengue viruses is typically asymptomatic or relatively mild, but if exposed to one of the other four viruses later in life an infected person has a greater risk of developing severe disease. This complex interaction between the four viruses and the human immune response has made developing an effective and safe vaccine against dengue very difficult. At present one vaccine has been licensed, but it can only be given safely to people who have already had dengue at least once.


Since we don't yet have a vaccine that can be widely deployed, controlling the mosquito vectors remains a very important approach in global dengue prevention efforts. In addition to environmental control and use of insecticides, a relatively new strategy that involves infecting mosquitoes with harmless bacteria called Wolbachia that interfere with the ability of dengue viruses to survive inside the mosquito is looking promising. Mosquitoes with different Wolbachia strains have been released in Australia and several countries in Asia and South America and trial results indicate that dengue cases numbers are reduced in places where these mosquitoes have become established in the wild population.

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