Zygoid

Zygoid, Zygoids or Fungis are slang terms for people with a neuroparasitic zygomycota based mycosis infection. An extreme form of zygomycosis, zygoids are infected with a unique strain of fungus that focuses on conscious creatures. They thus stay alive by living inside the hosts body including the nervous system and brain stem where hormones allow for an immense amount of control over the organism. 
Etymology 
Like other forms of zygomycosis 'zygoidism' is a mutation of a yeast and spore like fungus. Major differences come in the depth by which the infection lives within the hosts body. Along with the amount of control by which the parasite exerts control over the hosts daily function. 
Reproduction 
The fungus has two methods of reproduction or ways to spread to hosts. This would either be slowly through spore transfer from any of the long stalks that grow at night or from the local environment that these stalks terraform during the hosts sleep period. And quickly via an ovipositor like organ that sprouts for spore transfer from an infected individuals wrist directly into a victims flesh. 
Symptoms 
Infected individuals will experience fevers, delusions and a developing rash on the upper layer of the skin. If not treated the voices within the individual become increasingly prevalent until they become the dominate fixture and the hosts thoughts secondary. Only being prevalent when the fungus's own consciousness sleeps at night.
Issac 
Issac although not patient zero seeks to convert as many people as possible. With the overall promise of everyone withering away to death in a massive suicide. The goal then is to leave only non-conscious plants and fungi left on Terra.