Melioidosis is a disease caused by germs that occur naturally in certain parts of the world, such as Southeast Asia and northern Australia. The only places these germs, called Burkholderia pseudomallei, occur naturally in the United States is Puerto Rico and U.S. Virgin Islands. One reason public health authorities study the disease is because it is possible that the germs that cause melioidosis might be used in a biological attack. A biological attack is the intentional release of germs that can sicken or kill people, livestock, or crops.