This chapter describes the transmission of Brucella melitensis, as well as B. ovis and other Brucella species, among animals and to humans (B. melitensis). Goats and sheep are mainly infected by ingestion or inhalation of bacterium from contaminated organic and inorganic materials, fluids and air. Nevertheless, the conjunctival and dermal routes also play a secondary role in direct contact. Due to the significant amount of bacterium present in the reproductive system of infected adult animals, the uterine secretions and abortion products, the milk and the semen are the main contagious material responsive for the horizontal transmission. A vertical in uterus, or acquired by the consumption of colostrum and/or milk, transmission also can occur and are responsible for latent brucellosis, where lambs or kids are seronegative mainly until puberty. The lambing or kidding seasons represents a decisive moment for the dissemination of bacterium in flocks and environment. However, infected animals can excrete Brucella during long periods in asymptomatic and/or chronic forms. The bacterium can survive for several months especially in cold and humid environments, or in other fomites or vectors, and is responsible for an indirect contact transmission. Wild animals as well as the presence of dogs and other domestic animals in flocks can also be involved in the transmission of Brucella. B. melitensis, and B. abortus, which can also infect small ruminants, are the most serious pathogens in humans, and are transmitted by direct and indirect contact. A low number of bacterium, 10 to 100 microorganims, can be sufficient to cause the human disease.
