The reasons field trials outperformed lab experiments are unclear, although Carrington suspects it has to do with wild mosquitoes not getting the same nutrients as their pampered lab counterparts. Irrespective of the cause, however, the finding raises hopes wMel could make a major difference to the spread of this awful disease.
Carrington told IFLScinece field trials of other strains of Wolbachia have had the opposite outcome, proving less effective than lab tests had suggested. For example, Carrington said one version that shortened the lives of mosquitoes so they don't have time for the virus to develop to the point where it can be transmitted; "Also reduced the fitness of its host in other ways," making it unlikely to succeed in the wild.
We can't directly catch and infect enough mosquitoes to make Wolbachia widespread, but the bacterium has not been catching a ride on insects for millions of years without learning a trick or two itself. When an infected male and uninfected female mate, they produce eggs that don't hatch. As a result, infected females, who pass wMel on to the next generation, have a reproductive advantage. "Over a number of generations, the frequency of infected mosquitoes will increase in the population," Carrington told IFLScience.
Trials are now taking place in a number of countries where dengue is widespread, and Carrington hopes that if these produce similarly positive results, we may soon see dengue cases fall in those regions.