Dynamic Overview of Brucellosis Outbreaks in Humans and Animals in Bulgaria and the European Union

Brucellosis is a zoonotic disease with substantial public health and economic impact, requiring coordinated surveillance across human and animal populations. Bulgaria has historically been considered free of bovine brucellosis; however, re-emergence has been observed in recent years. The objective of this study was to analyze long-term epidemiological trends of brucellosis in humans and animals in Bulgaria (2002–2024).

Official surveillance data on laboratory-confirmed human cases and registered animal outbreaks were obtained from national and international databases. Descriptive statistics and linear regression analyses were performed using SPSS. Annual human cases were modeled against logarithmically transformed animal outbreak counts.

Globally, animal brucellosis outbreaks increased in most regions, with the largest rises in the Americas (46%) and Asia (10%), while Europe showed a 46% decrease. The largest number of human cases in the EU/EEA was reported in 4 countries, with sporadic cases in 10 other countries. In Bulgaria, re-emergence was concentrated in border districts. A statistically significant association was observed between annual animal outbreaks and human cases during 2006–2023 (R²=0.488; p=0.043). When 2024 data were included, the association was attenuated (R²=0.214; p=0.18).

The extensive integrated analysis of human brucellosis cases and registered animal outbreaks over the past decade supports updated mapping of human brucellosis worldwide, taking into account a complex of sanitary, socio-economic, and political conditions.

The findings on the emergence and re-emergence of brucellosis indicate renewed transmission risks and highlight gaps in prevention and surveillance systems despite advances in diagnostics.