Pig Zero
n.— «There is not yet any genetic proof that this particular flu was ever in a pig. […] Now, scientists say, the hunt is on for what is jokingly being called Pig Zero. “No one that I’m aware of has swabbed pigs for this yet.”» —“Virus’s Tangled Genes Straddle Continents, Raising a Mystery About Its Origins” by Donald G. McNeil Jr. New York Times Apr. 30, 2009. (source: Double-Tongued Dictionary)