INCIDENCE OF BACILLUS ANTHRACIS IN SOIL
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Interest in anthrax has increased recently due to its use in bioterrorism attacks. Bacillus anthracis, the causative agent of anthrax, is genetically similar to other Bacillus spp. that occur in the environment, and is known to persist in soil for years in the form of spores. In many soils, naturally occurring anthrax infections tend to occur during dry periods following a wet period. The "incubator theory" suggests that spores are concentrated in low-lying areas during rainfall events and animals are subsequently exposed to contaminated soil during foraging in dry periods. It is currently believed that B. anthracis spores require a host for germination, and thus do not undergo proliferation cycles in the soil. There is a potential for B. anthracis spores to be transported as an aerosol, but human infection due to inhalation of spores is unlikely given the high minimum infectious dose required to cause disease. Historically, naturally occurring anthrax infections in humans have most commonly occurred due to contact with diseased animals or animal products. However, B. anthracis has been developed as a biological weapon with accidental and intentional releases resulting in human death. With the development of an anthrax vaccine, anthrax outbreaks have generally been controlled in developed countries; however, anthrax is still a major problem in many parts of the world. The advent of molecular techniques has enhanced the detection of B. anthracis spores, which is now possible in less than 1 h. However, due to the persistence of spores, it is difficult to eliminate B. anthracis contamination from the environment. There remains a need for additional research on anthrax in several areas including evaluation of the conditions that favor B. anthracis survival in soil, determination of whether B. anthracis undergoes a growth cycle in soil, and determination of the potential for transfer of B. anthracis virulence genes to other soil microorganisms.
