MADISON, WI - JUNE 28: A research specialist at the AIDS Vaccine Research Labs at the University of Wisconsin-Madison processes blood samples taken from pregnant rhesus macaque monkeys infected with the Zika virus on June 28, 2016 in Madison, Wisconsin. Researchers at the University released a study today detailing how research at the facility has found the Zika virus persisted in the blood of pregnant monkeys for 30 to 70 days but only around 7 days in others. The study also found that monkeys previously infected with the virus were resistant to a second infection, which suggests the animals have a naturally occurring immunity. Health professionals in the United States are preparing for the possibility of an epidemic of Zika which can be transmitted by mosquitoes. (Photo by Scott Olson/Getty Images)
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