Wolbachia

Wolbachia is a group of bacteria that infects animal species. It is one of the world's most common parasitic microbes and is possibly the most common reproductive parasite in the biosphere.

History
Vocal cord parasites infected with a mutated strain of Wolbachia would cause them all to change into females, halting their reproduction and preventing their larvae from killing their human hosts, but at the cost of the human hosts' fertility.

Behind the scenes
Combating parasites harmful to humans using other parasites such as Wolbachia is a real-world subject of research.

Appearances

 * Metal Gear Solid V: The Phantom Pain