The Blue Death

The Blue Death is a deadly disease that began plaguing RiverClan during Applestar's leadership. The sickness was so fatal it forced RiverClan to leave their camp and retreat farther back into the forest, away from the river, where the effects lessened considerably.

Conditions
The Blue Death causes several different symptoms, including:
 * Seizures
 * Dehydration
 * Vomiting
 * Suffocation by foaming at the mouth

The only cat that has lived through The Blue Death was Timberfall, though his condition was less severe than other cats the disease has claimed.

Causes
The most known causes of The Blue Death included:
 * Drinking oil-polluted water
 * Being too close to oil-polluted water
 * Touching herbs or prey near oil-polluted water
 * Eating prey that has drank from oil-polluted water

The Blue Death in itself was caused by an oil spill in the river next to RiverClan.

Treatments
When it came to Timberfall's conditions, the most effective treatments included:
 * Keeping him on his belly so that he would be able to vomit without choking on it
 * Forcing-feeding him
 * Feeding him poppy seeds so that he would sleep without interruption

No known treatments apart from cleaning the oil pollution have been completely effective, however. Timberfall was only able to heal on his own.

Claimed Victims
Known victims that have died after catching The Blue Death include:
 * A RiverClan apprentice
 * Stormheart, Applestar's former mate
 * Several other unnamed RiverClan cats; no approximate number

Interesting facts

 * The Blue Death is based on Cholera, but the symptoms and causes are slightly different.