Wolfe works mostly in the forests of Cameroon tracking these viruses that can jump from animals to humans - what are called zoonotic viruses.

CNN: Tracking deadly viruses' spread from animals to humans

The H7N9 virus, previously known only to infect birds, appears to have mutated so that it can more easily jump to animals such as pigs, meaning the range of potential hosts has expanded.

WSJ: Bird Flu Worries Sink Airline Shares

The H7N9 virus, previously known only to infect birds, appears to have mutated so that it can more easily jump to animals like pigs, meaning the range of potential hosts has expanded, the Associated Press reported Wednesday, citing a World Health Organization scientist studying the virus's genetic makeup.

WSJ: China Bird Flu Cases Fuel Fears of Epidemic