The Zika virus is tenacious. In less than a year it has hopscotched to roughly 40 countries around the world, and more than 150 U.S. travelers have picked up the virus elsewhere and became sick at home, according to an exclusive Scientific American state-by-state count.

With the summer months ahead simmering concerns are now reaching a fever pitch for what the global outbreak could mean for the U.S. And the outlook does not look good. Top U.S. officials from two agencies have said they expect small clusters of disease—via local Aedes aegypti mosquito transmission—to erupt within the country’s borders, and there is also mounting evidence of male-to-female sexual transmission of the virus in humans.

In the absence of a vaccine against Zika, U.S. and World Health Organization officials are eyeing innovative solutions to help tamp down the outbreak, including using genetically modified (GM) A. aegypti mosquitoes that could outcompete the local population and tapping Wolbachia, a bacterium originally auditioned to combat dengue that could potentially keep infected mosquitoes from transmitting the virus.

Luciana Borio, the U.S. Food and Drug Administration’s acting chief scientist, told lawmakers today that her agency plans to “soon” release  a report for public comment assessing the environmental impact of small releases of genetically modified mosquitoes in the Florida Keys. The pilot project would be designed to test how these bugs would assist in a Zika outbreak. The male GM mosquitoes, produced by the U.K.-based company Oxitec, are modified to insure that when they mate with wild females their resulting offspring will die before adulthood (when females would feed on humans). Already, there have been more than 40 cases of travel-related Zika in the state and health officials are bracing themselves for local transmission of the virus from indigenous mosquitoes.

U.S. health officials’ largest concern, however, is the U.S. territory of Puerto Rico. “With Zika we could see hundreds of thousands of infections by the end of the year [in Puerto Rico],” warns Tom Frieden, director of the U.S. Centers for Disease Control and Prevention. By April, it is likely there will be “widespread” Zika there, he told lawmakers at a hearing today before a House subcommittee.

The numbers are not pulled out of thin air. Puerto Rico was bludgeoned in the past couple years with thousands of cases of another disease carried by the same mosquitoes called chikungunya. That disease, which causes joint aches, exploded across the country within a year of its arrival. The A. aegypti mosquito that transmits both Zika and chikungunya diseases is considered the “cockroach of the mosquito” Frieden says. It lives in the shade, is ubiquitous and is very hard to kill. It can breed in just a tiny amount of water and its eggs can lie dormant for long periods of time. Moreover, these mosquitoes have developed resistance to many traditional insecticides and bed nets are of little use preventing bites because these insects feed during the day.

Other pilot projects with Oxitec’s GM mosquitoes have proved successful at reducing mosquito numbers. Trials conducted in Brazil, Panama and the Cayman Islands all resulted in more than a 90 percent suppression of the wild A. aegypti population, according to the company. In trials in Piracicaba, Brazil, the company reduced wild mosquito larvae by 82 percent, Oxitec says. But whether this approach could be successful, sustainable and accepted in the U.S. remains to be seen. Borio told lawmakers, “We don’t know where the public stands.”