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Environmental management initiatives can also include major changes in a community, such as installing water systems with direct connections to residences and replacing wells and other water-storage containers, which can be mosquito-breeding habitats. Smaller-scale environmental changes can also be effective. For example, mosquito populations can be reduced when all members of a community clear blocked gutters and street drains and keep their yards free of containers with standing water. Any open containers should be emptied and cleaned each week to eliminate mosquito eggs and larvae. These efforts can reduce the number of mosquitoes living in an area.
What other measures can members of a community take to reduce mosquito populations? Community-based approaches must go hand in hand with educational initiatives that teach people about mosquito vectors and the risks of having mosquito-breeding habitats near their homes. Educational initiatives can encourage people to take an active role in participating in source reduction. Communities that understand the need to make behavioral changes are the most effective in controlling dengue. In addition to steps that communities can take, what can individuals do to protect themselves from dengue?
Could safer insecticides be used to kill mosquitoes? Bioinsecticides are a combination of biological controls and insecticides. One example of a bioinsecticide is Bacillus thuringiensis israelensis (Bti), which is a naturally occurring soil bacterium that can effectively kill mosquito larvae present in water. There are many strains of Bacillus thuringiensis, each having unique toxicity characteristics, and Bti is very specific for mosquitoes. Bti is available in small, slow-release bricks called "mosquito dunks" that float on the water surface and are effective in treating deep water. Other bioinsecticides, such as pyriproxyfen and methoprene, act as juvenile hormone analogues that prevent mosquito larvae from metamorphosizing into adults.
Recently, researchers used mosquitoes to transfer insecticides to larval habitats. They noticed that after taking a blood meal, female Aedes aegypti enjoy resting in damp and dark areas. To take advantage of this behavior, the researchers set up dark, damp stations dusted with a bioinsecticide that targets larvae. When the mosquitoes came to rest on the stations, their legs picked up the bioinsecticide and transferred it to the aquatic mosquito habitats where they laid their eggs. This method was effective in killing the mosquito larvae and reducing the number of adult mosquitoes. Are there any nonchemical approaches to reducing mosquito populations?
New genetic approaches are also being considered as ways to control mosquito populations. Researchers at the University of Oxford and Oxitec genetically engineered female mosquitoes that cannot fly. Being flightless is a huge genetic disadvantage. The flightless female mosquitoes are unable to "sing" and court with male mosquitoes using their wing oscillation "song." Predators can more easily prey on flightless female mosquitoes. The researchers theorize that these genetically engineered mosquitoes could be used to control mosquito populations and reduce dengue transmission. The same group of researchers recently genetically modified male mosquitoes to be sterile, and they released these mosquitoes in a trial in Grand Cayman, a Caribbean island, to wipe out dengue fever.
Dr. Scott O'Neill and his colleagues at the University of Queensland, Australia, came up with another innovative approach to control dengue transmission. These scientists infected mosquitoes with bacteria called Wolbachia pipientis, a parasite that shortens the lives of fruit flies. They hypothesized that Wolbachia could also shorten the lives of dengue-infected mosquitoes. Instead of eradicating mosquitoes, the scientists aimed to use the bacteria to shift the age of the mosquito population. Although mosquitoes would still be around, they would have shorter life spans than they do now. How would a shorter mosquito life span affect dengue transmission? When a mosquito is infected with dengue, eight to twelve days must pass before the mosquito can infect another healthy person, and after that period, the mosquito can continue to infect people for the rest of its life, generally three to four weeks. If its life span is shorter, an infected mosquito would have fewer opportunities to transmit dengue. O'Neill and his colleagues are currently testing another Wolbachia strain that seems to kill the dengue virus inside Aedes aegypti, which could serve as a dengue vaccine for mosquitoes.
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