The team creates a model of the virus causing an epidemic to better understand how it behaves and affects human cells. The novel virus changes continually, so it is difficult for them to create a vaccine.
A worldwide epidemic starts when humans cut down trees in an area inhabited by bats, forcing them to relocate. One bat carrying the virus dropped a piece of banana into a pig pen. One pig consumed the banana piece, and when it was slaughtered, the virus spread to the butcher's hands. The butcher did not wash his hands before he went to shake the hand of a guest, thus spreading the disease to the guest, who then spread it to other people.
Ralph visits Double Dan to get a virus that will allow him to slow down the Slaughter Race game. Double Dan shows him Arthur, a virus, and explains how Arthur works: he looks for defects in the programming and spreads it throughout the game.