20 November, 2012, Tiago Chiavegatti
A common bacterium that lives inside insect cells is the new weapon of an international effort to control dengue fever.
The new strategy, launched by the international program Eliminate Dengue, had encouraging results so far and could also be used against other diseases transmitted by mosquitoes such as malaria.
Professor Scott O’Neill, from the Monash University in Melbourne, Australia, is the leader of the initiative and is coordinating the first field tests with the bacterium in some Australian communities.
In addition to Australia,[frax09alpha] the project counts with scientists from research institutes of the United States, Brazil, Vietnam, Indonesia, Thailand and China.
Dengue fever is transmitted by the bite of female yellow fever mosquitoes (Aedes aegypti) carrying the dengue virus. Originally from Africa, these mosquitoes are now found in tropical and subtropical regions throughout the world. To reduce dengue transmission where the mosquito that could be carrying the virus lives, scientists released into the wild mosquitoes that were infected with a bacterium.
The bacterium, called Wolbachia pipientis, can stop the transmission of virus. Previous studies have shown that Wolbachia can reduce the life span of the mosquitoes and slow down the replication of the virus inside them.
The dengue virus thrives in the yellow fever mosquitoes because Wolbachia usually doesn’t infect them. To get to the virus living inside the mosquitoes, the scientists took bacteria that were infecting fruit flies and injected them into the yellow fever mosquito eggs.
Because the female mosquitoes transmit the bacteria to their offspring, scientists hope that this action will eventually make most of the mosquito population of the test areas become infected with the virus-blocker bacteria.
The scientists are using the field trials to see if the strategy can sustain a high rate bacterial infection within the mosquitoes and limit the transmission of the virus. The initial results seem positive.
According to a report issued last July, over 95% of the mosquitoes still had the bacteria six months after the release of the infected females in two of the tested areas. In only one region of the trial the infection levels were below 50%. The reason of this variability is still unclear, but the scientists suspect that climatic conditions favoring the wild non-infected mosquitoes could be the cause.
Similar trials are planned to happen next year in Vietnam and Indonesia, while another test in Brazil is scheduled to start in 2014.
To the entomologist Luciano Moreira, who works at the Brazilian institute partner of the international program, the biggest advantage is that this method is both safe and sustainable.
“It is a safe project, since this bacterium is already in nature. It is self-sustainable because, from the moment when it is release into the field, the bacteria are transmitted to the mosquito offspring. And, in addition, it is a non-profit [project]”, said Moreira to the news agency of the Brazilian research fund Fapesp.
Independent analysis found that Wolbachia is not harmful to humans, animals or the environment.
Contrary to yellow fever, for which a vaccine is available since 1936, the only way to prevent dengue fever so far is to control the mosquito population.
“Our strategy is complete compatible with other [population control measures]”, added Moreira.
“It will not be the only way to control dengue. People will still have to remove empty containers that may accumulate stagnant water where the mosquito breeds, and scientists should continue to research a vaccine.”
Dengue fever is a major health problem that causes between 50-100 million cases annually, according to the World Health Organization. It has been spreading around the globe with outbreaks that are becoming increasingly severe. The more extreme form of the disease, called dengue hemorrhagic fever, can be potentially fatal.
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