Pentapox

Pentapox is the name of a illness invented by Katara in the episode Return to Omashu for escape of the Fire Nation guards for the curfew.

Description
Katara told the guards that it was a deadly and highly contagious illness. The disease is characterized because the person presenting purple stains all over his body. The marks were made with an animal called Purple Pentapus; this animal adheres to the skin, leaving the stains.

Plague
Many citizens of Omashu escaped through an idea of Sokka. Sokka's plan was to make a false pentapox plague: people had to walk like sicks toward the doors of Omashu.