by
Heather Mayer, DOTmed News Reporter | April 05, 2010
Xi discovered that if a bacteria-infected male mates with an uninfected female, the embryo is killed. But he also found that when a female mosquito contains the same Wolbachia as a male, it can be passed on to the offspring, allowing the bacteria to spread quickly. His study found that there is a 100-percent maternal transmission rate.
"This bacterium can transmit from mother to offspring, which is very important," the researcher explains.
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The scientists are not sure how the bacteria stop the replication of dengue viruses in the insects, but they have two hypotheses. The first is straightforward, Xi says. The bacteria create immunity against the virus. The second thought is that because both the bacterium and virus live within the cells of the mosquito, there is a competition for the host's resources.
Efforts to create a vaccine for humans against dengue have been unsuccessful. The biggest reason, explains Xi, is because there is no animal model that can have dengue symptoms, thus no way to test a vaccine.
"Dengue is very unique in nature," he explains, as it only affects humans and mosquitoes. "Humans and mosquitoes maintain the virus very well."
The other challenge researchers are faced with is that there are four strands of the dengue virus, and having been exposed to one does not build up antibodies to fight the other strains. In fact, previous exposure to one type can strengthen a second strain, causing more severe symptoms, says Xi.
Currently, there are vaccines being tested in labs.
Out of the four strains of the virus (DENV 1, DENV 2, DENV 3 and DENV 4) DENV 2 is the most severe, says Xi. Reports and studies on dengue are generally based on this strain of the virus.
Moving forward, Xi and his team are using genomes of the bacteria, mosquitoes and viruses to learn how the bacteria work. The National Institutes of Health has awarded the team a $1.8-million grant for further research, which began in March 2009. There are four years left on this grant.
"This is an abnormal opportunity to study the effects" these organisms have on each other, Xi says.
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