Genophage Mass Efect
While this virus doesn’t have any painful symptoms that make you feel sick, it’s devastating for the Krogan species of the MassEffect universe. It was designed as a biological weapon to control the Krogans and works by making it difficult for females to carry any pregnancies to term, causing the species to slowly die out. Any female who can bring children to term is viciously fought over and seen as a prize of war. Knowing that their species is doomed most Krogans have become morose, which makes them even more dangerous than usual. Some would argue it’s justice as the Krogans were able to reproduce at such an alarming rate that they could drain planets of all of their resources, but it’s still a very cruel disease.