Zika-carrying mosquitoes eluding control efforts in Miami

Despite intense efforts to kill mosquitoes that carry Zika virus, the number of people infected via mosquito bites in Florida has surged. Ten new cases of locally-acquired Zika have been identified in the state, bringing the total of such infections up to 14.

Mosquito control measures in Miami “don’t appear to be working as well as we would have hoped,” Tom Frieden, director of the U.S. Centers for Disease Control and Prevention, said in a news briefing August 1. 

Florida has been spraying insecticides daily, but mosquito control experts are still seeing new larval mosquitoes and “moderately high” counts of Aedes aegypti, a species known to carry Zika. Mosquitoes in Miami may be resistant to the sprayed insecticides, or they could be holing up in hard-to-find breeding spots: small pools of standing water where larvae can hatch, Frieden said.

Health officials have pinned the area of exposure to a 150-meter radius around the workplaces of at least two infected people. It’s a swatch of mixed-use real estate just west of Biscayne Bay; the CDC has now warned pregnant women to avoid a one-mile zone surrounding the area. Infection with Zika can cause severe birth defects.

Frieden still doesn’t expect to see widespread transmission — A. aegypti don’t typically range far from home. And unlike with some mosquito-borne diseases (like West Nile virus), animals in the Miami area don’t seem to act as reservoirs for Zika.

But, Frieden cautions, in some small areas, especially where people live in crowded spaces or don’t have screens or air conditioning, Zika could stick around.