A contagious zoonosis affecting primarily horses, mules, and donkeys and caused by the bacterium Burkholderia (Pseudomonas) mallei. Glanders primarily involves the respiratory systems, skin, and lymphatics. It is marked by a purulent inflammation of mucous membranes and an eruption of nodules on the skin, forming deep ulcers. Glanders was once common throughout the world but is now found only in the Mideast and parts of Africa, Russia, Asia, and South America. Burkholderia mallei is a gram-negative, non-acid-fast, nonsporulating, nonmotile, unencapsulated bacillus occasionally showing bipolar staining; it is obligately aerobic and oxidase-positive. It is closely related to B. pseudomallei, the cause of melioidosis, a disease of humans and animals in Southeast Asia and northern Australia. Burkholderia mallei is highly infectious for humans, who may acquire it by handling or treating glanderous animals or during laboratory investigations. Untreated acute disease in humans has a 95% mortality rate within 3 weeks. There is no vaccine against infection. Burkholderia mallei is considered a category B biological agent because it is moderately easy to disseminate, causes moderate morbidity with high mortality in untreated cases, and requires special enhanced laboratory diagnostic capability.