Desolation Sickness

A parasitic mushroom spread by internal contact with spores, bloodfungus grows mycelium throughout the mortal body, feeding on the nutrients passed through the digestive tract and blood stream. After two months of relatively silent incubation, the mycelium will flower, bursting small fruiting-body stalks the size of an index finger from the skin along the afflicted’s appendages, which flower in a day and quickly begin to release spores. Further, the mortal’s nervous system is affected, producing extreme anxiety unless they seek out contact with other mortals.

Transmission & Vectors

Desolation sickness is caused by contact with spores emitted by the infected.

Causes

The disease starts when the victim is exposed to spores emitted by an infected person. The spores propagate in the blood, eventually causing finger-sized fruits to erupt from the skin, which release more spores. The spores ordinarily die quickly, except for the final exhalation of a dying sufferer, which can last for as long as 200 years.
A person exposed to desolation sickness (being within 5 ft of a person during the emission of spores) must makes a DC 14 Constitution Save or become Diseased.

Symptoms

The first noticeable symptom of desolation sickness is (as the name suggests) an overwhelming loneliness and crippling fear of being alone. A light fever persists for the whole run of the disease. Injuries suffered during the infection bleed paler than normal blood and make white scabs. The closer to fruiting the victim is, the paler their blood and the more pronounced their scabs are. After around 3 weeks, finger-sized fruiting bodies erupt from the skin, form bulbous heads and burst with yellow-brown spores.
For as long as the Diseased condition persists, the sufferer has the Shaken condition unless in the presence of (within speaking distance to) a creature of their own species. Additionally, they cannot regain HP by spending HD during a rest, and every damage dice they receive adds +1 necrotic damage. If the sufferer hasn't recovered by 3 weeks, they immediately take 3d6 necrotic damage. Every 8 hours, they take another 1d6 necrotic damage.

Treatment

A healer with the proper herbs can cure the sickness with little difficulty, if it's been identified. 
Someone proficient with a healer's kit can treat a sufferer during a long rest, at the end of which the victim will be cured. A Cure Disease potion or spell instantly kills the infection and allows normal healing to begin.

Prognosis

Without treatment, this disease is almost always fatal. With treatment it is almost never fatal.

Sequela

Feelings of loneliness can persist for months afterwards.
Someone who dies while infected becomes a 'desolate mummy,' a preserved corpse that appears perpetually fresh (3-4 days dead.) If disturbed, the corpse bursts in a 15 foot cube of spores. Mummies like this can exist for around 200 years if never burst.

Prevention

Avoiding contact with spores is the only sure way to avoid infection.
During outbreaks, rapid treatment is vital to prevent a crisis. Immediately burning infected corpse flesh is standard practice, as fire kills the spores.

Epidemiology

Outbreaks occur rapidly, usually with an infected adventurer or archaeologist wandering into town for some company. If the disease is quickly identified (which it usually is) then the death toll will be low to nonexistent. If for some reason a healer cannot quickly contain the infection, it can devastate an entire population.

Cultural Reception

For obvious reasons, people suffering from desolation sickness tend to be avoided when identified.
This has led to the occasional ostracization and unnecessary treatment of particularly needy people.

Type

Fungal

Origin

Mutated

Rarity

Rare