Scientists have started a trial in Cairns, northern Queenland releasing 60,000 mosquitos infected with wolbachia bacterium.

Short version: bacterium shortens mosquito's life to 12 days; mosquito must be 14 days old to transmit dengue.
Also researchers found that wolbachia immunises the mosquito against dengue, making it unable to pass on the disease.

I wonder if wolbachia could have the same affect on the West Nile virus?

I suggest Google search on dengue, wolbachia, and QIMR. I'm posting this way because none of the articles I found impressed me by themselves.

Edit: I think it may have been only 6000 mosquitoes released.