More than 20 people returning to the United States from Cuba have now been infected with or AUS virus also known as sloth fever. Federal health officials say it's spread to humans by small biting flies called midges and by some types of mosquitoes. Symptoms are similar to other tropical diseases like zika or malaria, including headaches and fever. Officials say so far nobody's died and they believe there is no evidence that it is spreading in the United States.