The Illinois director of public health says residents should guard against tick bites because the state has seen an increase in the tick-borne Rocky Mountain spotted fever. Doctor Damon T. Arnold said Friday that cases of the disease primarily have been reported in southern Illinois. Arnold says Illinois residents can protect themselves by wearing insect repellent and performing tick checks. Bacteria that spreads from ticks to humans causes Rocky Mountain spotted fever. The disease is not spread from human to human. If left untreated with antibiotics, it can be fatal. Symptoms include high fever, severe headache, and deep muscle pain.