Q: Is there such a thing as a Zombie fungus?
A: Unfortunately, yes there is.
Cordyceps, a genus of fungi that includes around 400 different species, is responsible for many deaths and Zombie-like behaviors in a wide variety of insects, the most famous among them the bullet ant.
When a Cordyceps fungus attacks a host, they invade and eventually replace the host tissues, using the host body as a base of operations for reproduction and relocation. Many Cordyceps release unknown chemicals into the host brain, causing disorientation, erratic behavior and eventually death; before finally sprouting through the body of the host and releasing their newly created spores.
Given enough time and the right conditions, this genus of fungus could evolve and effectively use Human tissue as a host. While the resulting Zombies would appear to hunger for Human flesh, they would actually just be driven neurologically to spread the fungus through blood, saliva, and tissue. Protection from the spores of such a fungus would be difficult, if not nearly impossible. The spores would no doubt survive heartily in the warm, moist, filters of most protective masks.