Dengue, also known as ‘breakbone fever’, is a mosquito-borne infection found in tropical and subtropical regions worldwide, particularly in urban and semi-urban areas. It causes a severe flu-like illness, and sometimes a potentially lethal complication called dengue haemorrhagic fever. The World Health Organization estimates that there are 50 million dengue infections annually. Approximately 2.5% of those infected die. Without proper medical care, fatality rates can exceed 20%.
Dengue is transmitted by Aedes mosquitoes, particularly Aedes aegypti and Aedes albopictus. Both species are closely associated with humans and both are also vectors of other diseases including yellow fever and chikungunya. Aedes aegypti is native to the Americas, while Aedes albopictus, the Asian tiger mosquito, has recently invaded the continent.
There has been a dramatic rise in dengue cases in the Americas over the past few decades. Disease cases in Central and Latin America have increased almost five-fold in incidence in the last 30 years. In 2007, there were more than 890,000 reported cases of dengue in the Americas, of which 26,000 were dengue haemorrhagic fever. The resurgence of dengue in Central and Latin America has been related to the collapse of Aedes aegypti mosquito eradication programs, human population growth, unplanned urbanisation with poor sanitary conditions, international travel and global climate change.
At present, the only way to combat the disease is to work to control populations of the vector mosquitoes. However, a number of vaccines have entered the human testing phases. In addition, research has led to two promising new natural control approaches.
In one study, researchers managed to shorten by one half the life span of Aedes aegypti by injecting the mosquitoes with a bacteria (Wolbachia pipientis). Because the dengue virus requires a relatively long period of development in its mosquito vector before it can be transmitted to a new human host, shortening the life of the mosquito should reduce the transmission of the virus. Moreover, the mosquitoes have a chance to reproduce before dying, passing on the bacteria to their offspring and thus producing more insects infected with the bacteria. Although field testing is needed, this research suggests that infection of mosquitoes by Wolbachia could become a viable strategy to reduce transmission of dengue and other mosquito-borne pathogens.
In another study, researchers created a new strain of Aedes aegypti mosquitoes in which females cannot fly. Only female mosquitoes bite and spread disease. When genetically altered male mosquitoes are released into the wild and mate with wild females, they pass on their genes, and females of the next generation are unable to fly. Flightless females are expected to die quickly in the wild. Scientists have estimated that if released, this new breed could suppress the native mosquito population in six to nine months and substantially reduce dengue transmission.
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