Patrick explains to Squidward about its supposed existence before Patrick and everyone else are informed by Dr. Gill Gilliam that it is a myth. The virus caused massive panic within Bikini Bottom, as it was feared that a bloodborne - and later an airborne - outbreak had started in the town. MSD was believed to be a highly contagious virus that caused rage in snails and zombie-like symptoms in fish and other creatures. This leads to mass hysteria and destruction throughout the town as residents were "infected" and "zombified" into zombies.
Squidward gets bitten by Gary and "infected" with Mad Snail Disease. When Patrick sees Squidward getting bitten by Gary, he tells Squidward that Gary has "Mad Snail Disease." SpongeBob tries to take Gary to Snail Care, but Gary escapes and bites nearly every Bikini Bottomite, supposedly starting a rage-filled outbreak of MSD.
As the last 'survivors' of the 'outbreak' watched in horror as the raging Gary bit SpongeBob, supposedly infecting him, Dr. Gill Gilliam tells the Bikini Bottomites that Mad Snail Disease is just an old urban legend and doesn't exist. He reveals that pain and irritation simply caused Gary's rabies-like symptoms from a splinter in his foot from Squidward's anti-snail defense. Gary wasn't infected, and he didn't start an outbreak of anything except for mass hysteria. The only thing inflicting Gary was Grouchy Snailitis.
Just as "the infected" broke into the fortified Krusty Krab, Squidward continues to groan like a zombie, albeit admitting he was not, and that he was groaning because he had to go to work.
- Ticklish ribs
- Loss of balance
- Bloodshot eyes
- Sore throat
- Messy pants
- Severely untrimmed toenails
- Large rash
- Flesh-craving zombification
- It appears to cause symptoms similar to rabies. However, this seems to be exclusive to Snails such as Gary, who was the source of the "outbreak".
- It is a parody of Mad Cow Disease.