In the TV series The Walking Dead, the characters inhabit a world overrun by zombies—specifically, zombies caused by a mysterious virus that has apparently infected everyone in the population. The living keep the virus in check by unknown means. But when someone dies—whether quickly after being bitten by a “walker” or felled by a human nemesis or more slowly due to natural causes—the result is the same: After death, everyone is reanimated as a bloodthirsty zombie.
It might not seem like things could get any worse, but as the group found out in this week’s episode, “Infected,” the zombie pandemic virus isn’t the only killer pathogen out there.
Why is a diagnosis important? The group decides in this episode to isolate people who are showing symptoms of the disease. (The next episode, in fact, is called “Isolation.”) If the pathogen is indeed swine influenza, and if it was already spreading among the humans in the prison, Rick’s step of sacrificing the piglets to the zombie horde would do little to nothing to stop the illness. If, however, it was S. suis, isolation probably wouldn’t even be necessary—keeping people away from the pigs should do the trick and end the epidemic.
Could such a diagnosis be made in the middle of an apocalypse? Definitively, probably not—but the group has both a veterinarian and a physician within the prison. It wouldn’t take much to do a crude epidemiological analysis, asking those who are coughing if they’d been exposed to pigs or how much time they’d spent around other (possibly sick) people. If all the sick people cluster together and haven’t been around the pigs at all, flu is a more logical choice, which may have originated in the pigs or the people. (An overcrowded prison, with people mixing from two recently assimilated communities, is certainly a great place for infectious diseases to spread.) To complicate matters, Rick correctly mentions to Carl at the end of the episode that the pigs could have made people sick or people could have sickened the pigs—many germs don’t care about species boundaries. There’s also the mysterious rat-feeder introduced in Sunday’s episode: Someone within the prison is catching live rats and feeding them to the zombie horde lingering outside the prison gates. Rats are notorious vectors of disease. Do they play a role in this new outbreak?