A quarter century of the re-emergence of Mediterranean spotted fever in Bulgaria

Abstract

Background: Mediterranean spotted fever (MSF), caused by Rickettsia conorii conorii is transmitted to humans by the brown dog tick Rhipicephalus sanguineus. In Bulgaria MSF occurred in two epidemic waves, the first (emerging disease) in 1948–1970, and the second starting after more than 20 years of absence (re-emerging disease) - in 1993. The aim of the study was to investigate the main epidemiological characteristics of the re-emerging MSF in the largest endemic region of Bulgaria – Plovdiv-city and suburbs. Methods & Materials: MSF was diagnosed by immunofluorescent assay in the Reference Rickettsioses Laboratory. All treated patients enrolled in the study were 1409. Results: MSF spread in the region in three distinct phases: first phase 1993-2003 with incidence of 11.88 per 100 000 populations, a second phase 2004-2011 with incidence 9.56, and third residual phase 2012-2017 with incidence 4.22. The age distribution of patients was similar as in the first phase: predominance of 40-59-year-olds (31.66%), reaching a peak in patients older than 60 years (37.5%). Children and adolescents till 19 years were less affected (18.12%), as well as the young people between 20–39 (12.7%). Urban population was almost twice as affected as rural population. The disease has summer seasonality, peaking in August. A skin eschar (tache noire) was found in average 77.91% of the patients. Mild forms of the disease were 41.16%, 35.63% and 45.80%; moderate forms were 32.79%, 43.12% and 33.54%; severe forms were 16.03%, 11.45% and 14.19%, and malignant forms were 6.56%, 8.54% and 5.80% for the phases I, II, and III respectively. The mortality rate was 2.45%, 1.25% and 0.64% resp. Despite the decline of spreading and predominance of mild and moderate course, the re-emerging MSF still presents with lots of severe and malignant forms, which makes a proportion of patients to be at serious risk of severe disease with complications and possible fatal outcome. Conclusion: A quarter century of its re-emergence in Bulgaria MSF is still potentially active despite the decreasing incidence and mortality rate.