Scientists are in a race against time in their efforts to stop the spread of the Zika virus. The World Health Organization estimates that as many as 4 million people could be infected with the Zika virus by the end of the year and, of course, the biggest fear is the virus' link to birth defects.

Until there's a vaccine against the Zika virus, controlling it comes down to controlling the Aedes aegypti mosquito that carries it. Countries in Latin America are aggressively spraying insecticides to kill adult mosquitoes, but more needs to be done.

Professor Peter Armbruster studies the Aedes albopictus, a mosquito that carries dengue, a virus related to Zika, at his laboratory at Georgetown University in Washington, D.C.

"Outdoor spraying has limited effectiveness in that these mosquitoes breed in a wide variety of container types that typically aren't going to be exposed when widespread spraying occurs," Armbruster said.

The mosquito that carries the Zika virus lays its eggs in old tires, water cisterns, bottle caps — any place where there's a drop or two of water.

Health agents remove plastic bottles during an ope
FILE - Health agents remove plastic bottles during an operation to eradicate the Aedes aegypti mosquito in Niteroi, Brazil, March 8, 2016.

"Insecticides can also be used to target the larval stages where the mosquitoes are living in their aquatic habitats," Armbruster said.

The downside to insecticide use is that other insects are also killed, and it leads to broad environmental exposure to insecticides. 

Other options

Other techniques use the Wolbachia bacterium to either sterilize the males or render the mosquitoes incapable of transmitting the virus. 

Some researchers are working to genetically modify the mosquito. Assistant professor Alexander Franz is doing that at the University of Missouri Department of Veterinary Pathobiology.

"We try to manipulate mosquitoes in such a way that they are resistant to these viruses. This way the transmission cycle can be interrupted," he said.

Franz said that in the past, his research group was able to produce genetically modified mosquitoes that were resistant to dengue. The idea is to release the virus-resistant mosquitoes into the wild, where they breed with wild mosquitoes and pass on the particular gene that resists the virus.

Another route is one being followed by Oxitec, a British firm that has modified the male mosquito so its offspring die before they can reproduce. Oxitec scientist Derric Nimmo told VOA that trials in the Cayman Islands and Brazil have reduced the wild mosquito larvae by more than 80 percent.

Brazil Zika Mosquito Eradication
FILE - A technician from the British biotec company Oxitec holds with a bag of blood to feed Aedes aegypti mosquitoes that were genetically modified to produce offspring that don't live, Feb. 1, 2016.

Nimmo said that, once the Aedes aegypti mosquito population falls to a level where it's no longer a threat, communities can monitor their numbers to determine if additional modified mosquitoes need to be released or if insecticides can do the job. With a plant in Brazil and a larger one in the works there, Oxitec is perhaps the company closest to having a ready solution. 

Armbruster said the most effective approach will involve a combination of methods.

"The most effective approach to suppressing the populations is going to be to take an integrated strategy that combines things like these genetically modified mosquitoes as well as traditional use of insecticides and elimination of breeding habitat," he said.

In the meantime, millions of pregnant women are depending on these scientists to come up with something quickly to spare their babies from the risk of enduring lifelong disabilities linked to Zika.