A 1948 New England Journal of Medicine report titled “Acute Brucellosis Among Laboratory Workers” shows us how actively dangerous this agent is. (1)
The laboratory workers were from Camp Detrick, Frederick, Maryland, where they were developing biological weapons. Even though these workers had been vaccinated, wore rubberized suits and masks and worked through holes in the compartment, many of them came down with this awful disease because it is so absolutely and terrifyingly infectious.
The article was written by Lt Calderone Howell, Marine Corps Captain Edward Miller, Marine Corps, Lt Emily Kelly, United States Naval Reserve; and Captain Henry Bookman. They were all military personnel engaged in making the disease agent Brucella into a more effective biological weapon.
(1) Howell, Miller, Kelly and Bookman, “Acute Brucellosis Among Laboratory Workers”, New England Journal of Medicine 1948;236:741.