Zika mosquitoes’ habits may foil U.S. elimination efforts


Health experts are bracing for Zika virus to spread to the United States by April or May, borne by a mosquito that craves human blood, feeds during the day and lives under beds and inside closets.

Until now, the best weapon against disease-carrying mosquitoes in the United States has been outdoor pesticide fog sprayed by truck and airplane. But health experts fear the typical approach will do little to eradicate the Aedes aegypti mosquito that carries Zika.

Controlling that mosquito requires pesticide sprayed under beds, on the walls and in closets, said Gonzalo Vazquez-Prokopec, who studies disease transmission patterns of mosquitoes at Emory’s School of Public Health’s Department of Environmental Sciences.

Though there could be localized U.S. outbreaks, most likely along the Gulf Coast, federal officials said they hope the wide use of air conditioning, window screens and regular garbage collection will mitigate the risk.

Florida Gov. Rick Scott declared a public health emergency in four counties with travel-related cases of the Zika virus on Wednesday and ordered state officials to increase mosquito control efforts in some of the most populous parts of the state.

“Although Florida’s current nine Zika cases were travel-related, we have to ensure Florida is prepared and stays ahead of the spread of the Zika virus in our state,” Scott said in a statement.

More than 30 people in the United States have been confirmed to have Zika after traveling to an affected country. There has been one report of transmission within the United States, but experts believe that will increase as the weather warms up, the local mosquito population multiplies and many more travelers return to the country.

The Aedes aegypti mosquito that carries Zika also transmits dengue fever and chikungunya. Aedes aegypti is mostly found in southern parts of the United States, such as the coastal regions of Texas, Louisiana, Mississippi, Alabama and Florida.

Experts believe it arrived on slave trade ships from Africa, spreading yellow fever in port cities, including a 1793 outbreak in Philadelphia that wiped out 10 percent of the city’s population of 50,000.

Unlike Aedes aegypti, most mosquitoes common to North America feed at night and live in wooded areas.

Recent research suggests the pest may be adapting to colder temperatures. David Severson at the University of Notre Dame discovered a population of Aedes aegypti mosquitoes that has spent the past four winters underground in Washington, D.C.’s Capitol Hill neighborhood.

Aggressive abatement involving indoor and outdoor fogging and breeding ground eradication between 1947 and 1970 nearly wiped out Aedes aegypti. At the time, the mosquitoes were the source of yellow fever across the Americas.

But budget cuts and the development of an effective yellow fever vaccine ended eradication efforts, and Aedes aegypti populations rebounded.

Scientists believe Aedes albopictus, or the Asian tiger mosquito, is also capable of spreading Zika. This aggressive biter arrived in the United States in 1985 and has replaced Aedes aegypti in some places. Its range includes at least 32 U.S. states as far north as Illinois and Pennsylvania and in pockets as far west as California.

Aedes albopictus breeds in small containers of water, bites during the daytime and lives near population centers. A less picky eater, it also feasts on pets and wild animals.

Researchers in Brazil are studying whether the Culex species, a carrier of the West Nile virus commonly found in many southeastern U.S. states, might carry Zika, which could explain the rapid spread in Brazil. These mosquitoes rest in the daytime and bite at dusk or after dark.