Climate-Sensitive Transmission of Human Brucellosis: A Systematic Review of Climatic and Environmental Determinants in the Middle East.

Background: Human brucellosis (HB) is a climate-sensitive zoonotic disease whose transmission is influenced by complex interactions among climatic, environmental, livestock, and human behavioral factors. Although the Middle East is a major climate change hotspot and remains highly endemic for HB, evidence regarding climate-brucellosis relationships has not previously been systematically synthesized. This review aimed to evaluate the influence of climatic and environmental determinants on HB across the Middle East. Methods: This systematic review was conducted in accordance with the PRISMA 2020 guidelines and prospectively registered in the Open Science Framework. PubMed, Embase, Scopus, and Web of Science were systematically searched from database inception to February 9, 2025. Studies examining the association between climatic or environmental factors and HB in Middle Eastern countries were included. Owing to substantial methodological heterogeneity, findings were synthesized using a structured narrative approach. Results: Thirteen studies met the inclusion criteria. Temperature and precipitation were each investigated in nine studies, whereas humidity was examined in five studies. Temperature demonstrated both positive and negative associations with HB incidence across different climatic settings, indicating context-dependent effects influenced by regional climate, ecological characteristics, and livestock management practices. Precipitation and humidity also showed heterogeneous associations, while wind speed consistently demonstrated a positive indirect association with disease occurrence. Seasonal analyses identified higher HB incidence during spring and summer, and vegetation cover was consistently associated with increased disease risk. Considerable heterogeneity was observed in study design, climatic settings, statistical methods, and adjustment for potential confounding factors. Because most included studies were observational, the reported associations should not be interpreted as evidence of direct causality. Conclusions: Climatic and environmental factors appear to play an important role in shaping HB transmission through interconnected human-animal-environment pathways in the Middle East. However, these relationships are highly context-dependent and influenced by ecological conditions, livestock management systems, and public health factors. Future multinational studies integrating climatic, environmental, veterinary, and epidemiological data within a One Health framework are needed to strengthen climate-informed surveillance, early warning systems, and brucellosis prevention strategies across the region.