Otter pox is a fictional illness in the world of PB&J Otter. It is a pun on the real disease, chicken pox. Much like the otter flu, judging by the name, only otters can get it. However, in the episode, Otter Pox, Opal told Jelly she couldn't come to her own birthday party because she had the illness, and her friends never had it. Which is ironic, because her friends are other animals besides otters. And it's called otter pox.