A farmer rearing sheep, presented with complaints of fever and weakness for the last one month. There is generalised lymphadenopathy. There was also associated hepatomegaly. Biopsy of liver showed non caseating granuloma. These are most likely due to infection with:

B. melitensis, which is the most common cause of symptomatic disease in humans and for which the main sources are sheep, goats, and camels. Overall, the presentation of brucellosis often fits one of three patterns: febrile illness that resembles typhoid but is less severe; fever and acute monoahritis, typically of the hip or knee, in a young child; and long-lasting fever, misery, and low-back or hip pain in an older man. Dual therapy with streptomycin and tetracyclines is the most effective treatment. Ref: Corbel M.J., Beeching N.J. (2012). Chapter 157. Brucellosis. In D.L. Longo, A.S. Fauci, D.L. Kasper, S.L. Hauser, J.L. Jameson, J. Loscalzo (Eds), Harrison's Principles of Internal Medicine, 18e.