Hate Plague

You've got red on you.

It's a madness plague, Galvatron. If one of those Transformers touches you, you're infected.Rodimus Prime, The Return of Optimus Prime, Part 1

The Hate Plague was one of the few maladies capable of affecting Transformers. Any organism, when infected, turns bright red and displays incredibly high levels of aggression toward everything and everyone.

Fiction

Generation 1 cartoon

It was first discovered in the 2-Part episode The Return of Optimus Prime in the third season of the G1 Cartoon, within the sun that the ship containing Optimus Prime's body was going to ram into.

Although extremely infectious (being instantly transmitted by touch, or by an extremely heavy concentration of the spores in the air), certain metals (such as the heat-resistant alloy featured in the same episode) can block the spores out. However, only pure, unadulterated knowledge could truly contain or defeat the spores; a wise man in pre-Cybertronian history was learned to have contained these spores within the sun they were found in, and at the end of the episode, Optimus was able to eradicate the spores by unleashing the accumulated wisdom within the Matrix of Leadership.

Beast Machines

In Beast Machines, Megatron uses a new variety of virus based on the Hate Plague in an attempt to destroy the Maximals.

From Teletraan I: The Transformers Wiki, a Wikia wiki.