Ichthyophthirius Evolution
Ichthyophthirius multifiliis, AKA Ich, is a common parasite found in freshwater fish, but testing on said parasite by an organization called Plague Inc. led to an unexpected mutation.
With Ich now able to spread to humans, you have a chance to infect and wipe out all of humanity. But watch out, EVERYONE will be trying to stop you.