Burkholderia mallei |
|
Burkholderia mallei (also previously designated Pseudomonas mallei, Bacillus mallei, Pfeifferella mallei, Acinetobacter mallei, Loefferella mallei, Malleomyces mallei, and Actinobacillus mallei) has been identified as the causative agent of glanders (also known as equinia, farcy, malleus, droes). Most known members of the Burkholderiaceae are resident in the soil, however, B. mallei is an obligate mammalian pathogen. Horses are its natural reservoir, although mules, donkeys, goats, dogs and cats are also susceptible to infection.
Glanders is an ancient disease that has followed human civilization, and has been described in writings by ancient Greek and Roman writers, Shakespeare, and Alexandre Dumas. No naturally transmitted cases have been reported in the US since the 1940's, but it is endemic in Africa, Asia, the Middle East, and Central and South America. The disease has a 95% fatality rate for untreated septicemic infections and a 50% fatality rate when standard antibiotic treatments are administered, and it is difficult to diagnose. The course of infection depends upon the nature of exposure. Direct contact with a cut or scratch can lead to a localized cutaneous infection. Inhalation of aerosol or dust containing B. mallei can lead to septicemic, pulmonary, or chronic infections of the muscle, liver and spleen. Survivors of glanders develop no protective immunity, and thus are susceptible to future infections. B. mallei is a member of the betaproteobacteria. It is rod-shaped and non-motile, and produces an extracellular capsule which is an important virulence determinant. It can survive drying for 2-3 weeks, but is susceptible to heat and ultraviolet light. The B. mallei strain ATCC23344, isolated in 1944 out of post-mortem cultures, was recently sequenced. The genome consists of two chromosomes comprising ~5.7 million base pairs. Its sequence is riddled with insertions sequences that have had a dramatic effect on its chromosomal structure. Glanders has been associated with war for centuries. The concentration of horses required for moving supplies and troops spread disease among horses and humans until modern times when motorized vehicles took the place of animals. In World War I B. mallei was used as a weapon for the first time. The Central Powers infected Russian equines, causing disruption of supply lines and associated human deaths. The Japanese used it in World War II against the Chinese, and there is anecdotal evidence that the Soviet Union attempted to weaponize B. mallei in the 1980's and used it in Afghanistan. The United States considered developing it as a bioweapon in the 1940's, but ultimately did not. Its ease of transmission and severity of disease have made B. mallei an obvious choice as an agent for bioterrorism, and the US NIAID has categorized B. mallei as a Category B Biological Disease. Other web resources: Center for Disease Control Chemical and Biological Warfare Agents Virginia Bioinformatics Institute PATHPORT Emedicine |
