Mega Bite

Mega Bite was the rather affectionate name given to a horde of mutated fleas which swarmed various underground parts of Raccoon City (most commonly in the subway system) after the water supply was contaminated with the t-Virus.

They were most likely created when they lived on an infected animals fur and got the infection themselves after consuming their blood. When infected, they grew to enormous proportions, no longer able to hide under floorboards or in dark corners - they abandoned their parasitic behaviours and simply attacked prey directly and consumed their blood. Then, they would lay a clutch of eggs on the corpse of its last victim, for them to later emerge as young and then immediately feeding on the corpse, allowing it to grow into an adult at an alarming rate.

Cosmetically, they grow proportionally - they literally are scaled up fleas. Interestingly, they can grow to ridiculously big sizes in certain situations as there has been the existence of the even bigger Giga Bite flea.

Although it would be safe to assume that t-Virus infected fleas should exist in other places as Zombie Dogs and other similar creatures exist (and at least a proportion of those would likely have fleas) they have never been seen outside of Raccoon City.