Indian Journal of Animal Sciences 91 (11): 885–890, November 2021/Review Article Main risk factors associated with small and large ruminant brucellosis MARYAM DADAR 1 and JACQUES GODFROID 2 Razi Vaccine and Serum Research Institute, Agricultural Research, Education and Extension Organization, Karaj, Iran Received: 25 August 2021; Accepted: 7 September 2021 ABSTRACT Brucellosis is a neglected zoonotic bacterial disease in most of the developing world that has a significant impact on public health. The prevalence of brucellosis in livestock, particularly in large and small ruminants is variable in many countries and seems to remain high, especially amongst subsistence and small-scale livestock farmers. There are different factors that may influence the prevalence of brucellosis in large and small ruminants. This review is aimed at describing the most important factors that need to be taken into consideration for the planning and implementation of effective brucellosis control programmes. Common risk factors in the brucellosis development in small and large ruminant animals include species, age, sex, extensive or intensive production system, herd/flock size, mixed farming, introduction of new animals in the farms, breeding practice, hygiene, absence of vaccination, and awareness of the disease. This review suggests that different risk factors might have various impacts on brucellosis seroprevalence that need to be addressed in epidemiological studies in different farming systems. Keywords: Brucellosis, Large ruminant, Risk factor, Small ruminant 5 Present address: 1 Razi Vaccine and Serum Research Institute (RVSRI), Agricultural Research, Education and Extension Organization (AREEO), Karaj, Iran. 2 Department of Arctic and Marine Biology, Faculty of Biosciences, Fisheries and Economics, UiT-The Arctic University of Norway; Tromsø, Norway.  Corresponding author email: dadar.m77@gmail.com According to the World Health Organization (WHO), the Office International des Epizooties (OIE), and the Food and Agriculture Organization (FAO), brucellosis is still one of the most widespread and important zoonotic infection in developing countries (B Lopes et al. 2010, Seleem et al. 2010). This disease is a source of different economic concerns because of infertility in both sexes and late term abortion (Sulima and Venkataraman 2010, Angara et al. 2016, Awah-Ndukum et al. 2018, Deka et al. 2018, Franc et al. 2018), decreased milk yield (Herrera et al. 2008, Mellado et al. 2014), loss of draught power and market value of animals, missed reproductive cycle, decreased productivity, increased veterinary costs, and birth of weak offspring with low birth weight in farms (Blasco and Molina-Flores 2011, Dadar et al. 2020, Lokamar et al. 2020). Brucellosis is a chronic and infectious zoonotic disease of domestic and wild animals caused by several species of Brucella bacteria (Franc et al. 2018). Currently, twelve species could infect different domestic and wild animal species (Whatmore et al. 2016). Among them, six Brucella species have been divided based on their preferred hosts and pathogenicity as Brucella melitensis (goats and sheep), Brucella abortus (cattle), Brucella suis (pigs), Brucella ovis (rams), Brucella canis (dogs), and Brucella neotomae (desert wood rat, common voles). B. melitensis, B. suis, and B. abortus are known as the most important pathogenic species in livestock (Omer et al. 2000, Lindahl et al. 2014, Wareth et al. 2014, Kaynak-Onurdag et al. 2016, Whatmore et al. 2016, Dadar et al. 2019a), while Brucella. melitensis is the main source of human infections (Dadar et al. 2019a, b). Beside well-known endemic regions located in Africa, South and Central America, the Mediterranean Basin, Middle East, and Asia, brucellosis remains a neglected disease in several areas which can lead to serious economic concern for the livestock industry (Sulima and Venkataraman 2010, Santos et al. 2013, Mableson et al. 2014, Bamaiyi 2015, Singh et al. 2015). The aim of this mini-review is to highlight the potential risk factors for Brucella infections in small and large ruminants. Brucellosis in large ruminants Brucella abortus has been known as a Gram-negative coccobacillus bacteria in the class Alphaproteobacteria, family Brucellaceae that commonly infects cattle and other bovinae as the primarily hosts. Brucella abortus is divided into eight biovars (1–7, 9), of which biovars 1 to 3 are the most commonly isolated biovars from humans. Brucella melitensis, B. canis and B. suis have been reported as other Brucella species that could be isolated in cattle (Khurana et al. 2021). Reservoir hosts of B. abortus are reported as cattle, water buffalo, African buffalo, American bison (Bison https://doi.org/10.56093/ijans.v91i11.118115