[Name] Cluckitis [Source] The Muppet Show [Symptoms] 
A victim of this highly contagious disease turns into a chicken; victims retain their true voices and mannerisms, but some develop chicken-like habits, like building nests. After almost every Muppet catches it, guest star Roger Miller (who claims to have had it once) assures Kermit that it goes away by itself in a few days. Also, because Gonzo doesn't catch it, and he tends to hang around chickens a lot, he likely has developed an immunity to it.