If the most efficient dengue fever carrier, a mosquito called Aedes aegypti, establishes itself in California, it wont be because the state didnt put up a fight. We would like to eliminate the mosquito, says Steve Mulligan, a manager with the Consolidated Mosquito Abatement District, but at this point all were doing is trying to control its spread. Tim Phillips, Mulligans counterpart at the Fresno Mosquito and Vector Control District, agrees. In just under six months, the invasive bug has spread to at least four counties and continues to widen its foothold in central California. But what most Americans dont know is that the dengue virus was once common in the US — and could be again.