Narrator: This is Science Today. The West Nile virus first emerged in the United States in 1999. The virus, which lives in birds and other animals, can be transmitted to humans by mosquito bites. Research entomologist Bill Reisen of the University of California, Davis is using satellite data and remote imagery to better monitor and manage West Nile Virus in California and eventually, other Western states.

Reisen: Our research has been really to track this whole movement and decide how the virus persists and then amplifies to levels to start infecting humans.

Narrator: During the winter months, when it's too cold for the virus to grow in mosquitoes, Reisen says it's very difficult to find.

Reisen: A winter focus of our research has been trying to decide how it spends the winter. Up north, it may spend the winter in hibernating mosquitoes, whereas in areas like Los Angeles , there may be a just very low level of continued transmission. But we're still trying to gain data on this, as to how the virus does this.

Narrator: For Science Today, I'm Larissa Branin.