To combat the persistent scourge of dengue fever, researchers have infected the virus-carrying mosquitoes with a bacterium that kills them before they’re old enough to transmit the virus to humans. Researchers say this “biopesticide” technique could cheaply and quickly reduce deaths due to dengue fever in the tropics, as the bacterium could rapidly spread through mosquito populations. Traditional [malaria-oriented] methods for controlling the spread of mosquito-borne disease, such as using bed nets and draining wetlands, are ineffective for the Aedes aegytpi mosquitoes that spread dengue fever virus because they bite during the day and thrive in urban areas [Nature News].
While the new process has only been tested in the lab thus far, researchers are very optimistic about the possibility of whittling away at the 20,000 deaths caused each year by the disease, and say it’s conceivable that transmission of the virus could be reduced to nearly zero. “We’re not trying to eliminate the population, but to let a bacterial symbiont in, and then shift the population,” said University of Queensland bacterial geneticist Scott O’Neill. “There will still be mosquitoes around, but only young ones. It’s a biological control” [Wired News].
In the study, published in Science [subscription required], researchers explain that the dengue fever virus incubates in the mosquito for several weeks before it can be transmitted via a mosquito bite. O’Neill wondered if he could use a common bacterial parasite called Wolbachia that shortens the lives of fruit flies to kill off mosquitoes before they became full-blown disease vectors. But repeated efforts to infect mosquitoes with Wolbachia failed until … his team cultured the bacteria in dishes of mosquito cells for three years. The microbes adapted to their new host species’ cellular environment [Wired News]. Mosquitoes infected with the adapted bacteria lived about 21 days, while control mosquitoes lived for 50 days in the comfortable lab conditions. As wild mosquitoes have shorter lifespans, they would likely die even sooner if infected.
The mosquitoes do live long enough to reproduce, and infected mothers pass down the bacterium to their offspring; what’s more, when an uninfected female mates with an infected male, the female becomes sterile. These two factors may allow Wolbachia to spread rapidly through the mosquito population, researchers say. There are still a number of questions to answer, including whether the dengue virus will evolve to incubate faster if its hosts begin dying younger, and whether the altered bacteria will spread to other species. But O’Neill says if field tests in far north Queensland are successful, a pilot program could be running by 2012 [ABC News].
O’Neill says an advantage of his ‘biopesticide’ approach is that it is more likely to get regulatory approval than other ongoing attempts to control the spread of dengue fever by genetically modifying the disease-carrying mosquitoes [Nature News]. Meanwhile, infectious disease experts are hopeful that one or the other technique will prove successful, as dengue fever is expected to spread north as global warming changes weather patterns.
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Image: CDC / James Gathany