When the USDA issued an announcement on Oct. 30 that the worrisome H5N1 bird flu turned up in a pig, I dropped what I was doing to read it. The situation didn’t quite match the nightmare scenario some experts described to me last spring, in which this virus starts rampaging through commercial pigs. But it’s worrisome.

Spreading through big, industrial pig farms would give the virus ample opportunity to evolve into a form capable of causing a pandemic in humans. Pigs remain at the center of scientists’ nightmare scenario because commercial swine carry lots of human flu viruses. Their cells share enough features with ours that flu viruses can use some of the same entry ports, known as receptors.

Fortunately, the case reported recently involved only a private backyard farm in Southern Oregon. The infected pig was reported to be asymptomatic and a miniature potbellied pig on the same farm was also reported to have tested positive. All the pigs at the farm have been euthanized and the farm quarantined. So it’s not the start of a disaster, yet, but a warning that it’s important to improve surveillance to better understand this strange, ever-changing virus.