Rising Sickness

The rising sickness is a virulent and deadly disease caused by exposure to necrotic magic, so named because those who die from it are doomed to rise again as a zombie capable of spreading the disease further.

Causes

Outbreaks of the rising sickness are rare, and thankfully tend to be short lived. Each outbreak has been associated directly with necrotic magic, often involving cursed artifacts and locations, such as the field of decay used in Caelester's sewer system. Primarily because of this, such artifacts are regularly destroyed and access to such regions is heavily restricted and limited to those bearing suitable magical protections.
Due to the stigma on research into this school of magic, the exact circumstances required to induce the rising sickness in a victim are not well understood, though it seems that in most cases, this is an unintended side effect of exposure to necrotic energies rather than a deliberate curse wrought by a master necromancer. As such, any mortal foolish enough to explore this form of magic takes their lives into their own hands, particularly if they do not equip themselves with appropriate protections.
Once an outbreak has begun, the sickness becomes communicable by sharing bodily fluids with a victim. In most cases, this only happens when the initial victim dies and rises again as a zombie. Such zombies are typically much more prone to biting than those raised by other means, and transmit the disease through their saliva.

Symptoms

The rising sickness progresses quickly, often killing its victims in a matter of hours. Those exposed report feeling an unnatural chill in their extremities, which begins quickly, especially when exposed through the bite of a zombie. In as little as two hours, this progresses to a dry cough and paling of the skin, followed quickly by the onset of unusual stiffness coupled with an insatiable hunger and excessive salivation. The victim's hair becomes brittle and can be pulled out without resistance, and skin shrivels up and withdraws, with fat deposits seeming to be consumed by the disease. Eventually the muscles freeze up in a manner eerily similar to the phenomena of rigor mortis, and breathing grows increasingly laboured and soon ceases. This entire process, from exposure to death, can take as little as twelve hours, though on average it takes 24 hours, with some particularly hardy individuals lasting for days. Full recovery is generally believed to be impossible without magical intervention, and those in the latter stages can take weeks to return to normal even with such assistance.
Sadly, of course, the rising sickness does not end with the victim's death. In the 20 minutes following a victim's demise, necrotic energies surge through the corpse, sometimes causing it to write as if in extreme pain. At the conclusion of this, the corpse rises, seeks out a victim, and attacks. Horrifyingly, these zombies tend to ignore people once they have been bitten, with some reports even suggesting that they seem to know if a bite victim has been infected or not. Indeed, there are documented cases where zombies have run past extermination parties who had been infected, ignoring the still active warriors attacking them in favour of seeking more people to infect.

Treatment

The rising sickness is treated through restorative magic, often fueled by the divine. The disease's progress can be slowed through simple protective charms, which are often employed to buy time for the application of more complex curative magics, such as those capable of curing diseases or removing curses. More sophisticated magics can be applied to speed recovery, but these are typically reserved for those in the final stages of the disease, as outbreaks tend to claim enough victims that healers must ration their abilities.
In the brief window between death and rising, nothing short of decapitation or burning can prevent the corpse from rising again. During this stage, the necrotic energy is forming a structure capable of animating the corpse, and is highly adaptive - it takes extreme damage to the body to entirely disrupt this process.
For the risen, there is no other recourse than to put them to the sword, as with any other zombie. This is typically accomplished by the most capable warriors available, and in an organized response, such people are offered either a blessing or magical relic capable to help protect them from the disease.