11. West Nile Virus
The West Nile Virus happens to be one of the deadliest diseases on the planet today. It is exclusively spread by mosquitoes, often found in multiple places around the world. However, it is the leading cause of mosquito-borne disease in the continental United States today. A person gets this by being bitten by a mosquito, but may not see any symptoms at all initially. While 1 in 150 people who get West Nile have an issue with their central nervous system due to the disease, this could be more.
Essentially, if a person weaponized West Nile then they could make a virus that attacked the central nervous system exclusively or with other areas. Many get a fever with the issue, however, others see it much worse. Disorientation, tremors, convulsions, numbness, paralysis, and stupor occurs. If weaponized, all of this could be more intense and possibly even controlled. Thus, a real zombie apocalypse could come out of it.