Anthrax is primarily a disease of herbivores. Humans and
carnivores are incidental hosts.
Anthrax is an infrequent and sporadic human
infection in most industrialized countries. It is an occupational
hazard primarily of workers who process hides, hair, (especially from
goats), bone and bone products and wool; and of veterinarians and agricultural
and wildlife workers who handle infected animals. Human anthrax is
endemic in those agricultural regions of the world where anthrax in
animals is common. These countries include South and Central America,
southern and eastern Europe, Asia and Africa. New areas of infection
in livestock may develop through the introduction of animal feed containing
contaminated bone meal. Environmental events, such as a dry period,
followed by heavy rains and/or flooding, may provoke epizootics.
Anthrax is considered a leading potential agent in bioterrorism or
biowarfare and, as such, could present in epidemiologically unusual
circumstances.
Animals (normally herbivores, both livestock and wildlife) shed the
bacilli in terminal hemorrhages or spilt blood at death. On exposure
to the air, the vegetative forms sporulate, and the spores of Bacillus
anthracis, which are very resistant to adverse environmental conditions
and disinfection, may remain viable in contaminated soil for many years.
Bacillus anthracis is a soil commensal in many parts of the world.
Bacterial growth and spore density in soil are enhanced by flooding
or other ecological conditions. Soil can also be contaminated by vultures,
gulls,or ravens, which spread the organism from one area to another
after feeding on anthrax infected carcasses. Note - Most birds, except
ratites, are naturally resistant. Dried or otherwise processed skins
and hides of infected animals may harbor the spores for years and are
the fomites by which the disease is spread worldwide.
Cutaneous infection is by contact with tissues of animals dying of
the disease. Biting flies that had partially fed on infected animals
have also been implicated as a source of infection. Contact with contaminated
hair, wool, hides, or products made from them, or by contact with soil
associated with infected animals or contaminated bone meal used in
gardening, have been documented as sources of infection.
Inhalation anthrax results from inhalation of spores in risky industrial
processes, such as tanning hides and processing wool or bone, where
aerosols Bacillus anthracis may be produced. Intestinal and
oropharyngeal anthrax arise from ingestion of contaminated undercooked
meat. There is no evidence that milk from infected animals transmits
anthrax.
The disease spreads among grazing animals through contaminated soil
and feed. The spread among omnivorous and carnivorous animals is through
contaminated meat, bone meal, or other feed, while the spread in the
wildlife population is from feeding on carcasses infected with anthrax.
The following sites provide further information on this disease:
