Simplify the following text for a Grade 9 native English-speaking person.
Original: Tularemia ( also known as Pahvant Valley plague , rabbit fever , deer fly fever , Ohara 's fever ) is a serious infectious disease caused by the bacterium Francisella tularensis .
Simplified: Tularemia ( also called `` Goblin Fever '' , `` deer-fly fever '' , `` Ohara fever '' and `` Francis disease '' ) is a disease .