Who discovered the causative agent of brucellosis?

David Bruce discovered the bacterium that causes brucellosis.

In 1887, while investigating Malta fever in the British military community on Malta, Bruce isolated the organism now known as Brucella. At the time, he called it Micrococcus melitensis. The disease was also known as undulant fever or Malta fever before the modern name brucellosis became established.

Bruce’s work showed that the disease had a specific bacterial cause, but the later history involved several contributors. Themistocles Zammit experimentally demonstrated in 1905 that infected goats and their milk were central to transmission. That finding explained why soldiers and residents who consumed unpasteurized goat milk were at risk.

The genus Brucella was named in Bruce’s honor. Brucellosis is a zoonosis: people can acquire it through unpasteurized dairy products, contact with infected animals or animal tissues, inhalation of laboratory aerosols, and, less commonly, other routes. It is not caused by one universal species; Brucella melitensis is especially associated with goats and sheep, while other species favor cattle, pigs, or dogs.