A rare virus has turned up at a handful of chicken farms in northern Indiana.

It’s called Egg Drop Syndrome, and it causes otherwise healthy chickens to lay eggs with extremely thin, discolored shells — or in some cases no shell at all. The virus is not fatal to chickens and is unable to spread to humans. But it does impact the number of eggs that farmers produce.

Indiana is the second largest egg producing state in the U.S, producing more than nine billion eggs a year.