Cackle fever

Cackle fever, also known as "the shrieks", was a disease that caused uncontrollable and debilitating fits of laughter.

Acquisition
The disease spread through the air such as through the sneeze of an infected carrier. It was highly contagious such that merely standing within of an infected individual ran the risk of immediately catching it. Cackle fever only affected and spread between humanoids. Gnomes were immune to the disease for some unknown reason, but could still act as asymptomatic carriers of it.

It was also possible to contract cackle fever from ghosts and from noxious gasses in the Great Swamp of Rethild.

Cackle fever was one of several diseases that could be inflicted using the contagion spell.

Effects
Symptoms manifested within a day, potentially in as little as one to four hours. Often, infected individuals did not know they had cackle fever until they encountered a stressful situation that brought on a bout of inexplicable and uncontrollable laughter. Sufferers of cackle fever experienced disorientation and high fevers alongside these frequent fits of hideous laughter, which could last up to a minute. The most severe bouts of laughter could be completely debilitating and even cause psychological harm: these erupted in response to stressful or frightening situations, such as combat, being injured, or having a nightmare.

As the disease progressed, it caused a steady deterioration in willpower, perceptiveness, and common sense, and ultimately it could leave sufferers fully catatonic or cause them to go mad.

Treatment
Usually, healthy individuals could slowly but surely fight off the disease naturally. It could also be cured magically, however in its most advanced stages, spells and rituals like cure disease might only offer temporary relief to the sufferer.

History
Black Wagon Alley in Waterdeep was haunted by a ghostly plague wagon that was said to spread cackle fever to those that beheld it.

At some point prior to the late 14 century DR, the lich Zzarka created a disease she called "cacklefire" by combining cackle fever and mindfire.

In the late 15 century DR, the disease was present on Avernus. The gnome archmage Pingle attended a grand ball hosted by the devil Qirozz and unknowingly spread it among the humanoid guests.