Wanted: Ebola
Ebola is a retro-virus that is primarily found in West Africa. It mostly targets weaker immune systems but that doesn't stop it from attacking everyone else.
Ebola is spread through contact with infected body fluids. When in the body it attacks immune cells and eventually kills its host.
Ebola is one of the most dangerous and unstoppable viruses when inside the body. There is no defense when it attacks.