The U.S. government has begun scattering millions of packets of oral rabies vaccine from helicopters and planes in 13 states from Maine to Alabama. The major aim is to help keep raccoons from spreading their variant of the deadly virus to states where it's less prevalent. The government is also continuing tests of a vaccine that Canada has approved to immunize skunks as well as raccoons. Rabies is generally spread through an infected animal's saliva. In the U.S., pet vaccination laws mean it's mostly spread by wildlife.