Mediterranean spotted fever--classification by disease course and criteria for determining the disease severity.

Introduction: Mediterranean spotted fever (MSF) in Bulgaria is caused by Ricketsia conorii conorii with a major vector the dog tick, Rhipicephalus sanguineus. The first cases of re-emerging MSF were reported in this country in the early 1990s after some 20 years of absence and then registered an annual increase until 2001-2003 after which the disease prevalence declined. MSF still poses a serious health problem in the country as severe, complicated cases with lethal outcome occur.