|
The Epidemiology of Anthrax
Anthrax occurs worldwide. The organism exists in the soil
as a spore. Animals, domestic or wild, become infected
when they ingest spores while grazing on contaminated land or eating
contaminated feed. Only when the organism in the carcass is
exposed to air does sporulation occur. Environmental
conditions such as drought, which may promote trauma in the oral
cavity on grazing, are thought to increase the chances of acquiring
anthrax, as Pasteur originally reported1.
Anthrax in humans is associated with agricultural, horticultural,
or industrial exposure to infected animals or contaminated animal
products. In the less-developed countries, primarily in Africa,
Asia, and the Middle East, disease occurs from contact with infected
domesticated animals or contaminated animal products. This includes
handling contaminated carcasses, hides, wool, hair, and bones; and
ingesting contaminated meat. Cases associated with industrial
exposure, rarely seen today, occur in workers processing
contaminated hair, wool, hides, and bones. Direct contact with
contaminated material leads to cutaneous disease, while ingestion of
infected meat gives rise to oropharyngeal or gastrointestinal forms
of anthrax. Inhalation of a sufficient quantity of spores, usually
seen only during generation of aerosols in an enclosed space
associated with processing contaminated wool or hair, gives rise to
inhalational anthrax.
Unreliable reporting makes it difficult to estimate with accuracy
the true incidence of human anthrax. It was estimated in 1958
that worldwide between 20,000 and 100,000 cases occurred annually2.
In more recent years, anthrax in animals has been reported from 82
countries, and human cases continue to be reported from Africa,
Asia, Europe, and the Americas3. In the United
States, the annual incidence of human anthrax has steadily
declined—from about 127 cases in the early years of this century to
about one per year for the past 10 years. The vast majority of
cases have been cutaneous. Under natural conditions,
inhalational anthrax is exceedingly rare, with only 18 cases having
been reported in the United States in the 20th century4.
In the early years of this century, cases of inhalational anthrax
were reported in rural villagers in Russia who worked with
contaminated sheep wool inside their homes5. Five
cases of inhalational anthrax occurred in woolen mill workers in New
Hampshire in the 1950s6. During times of economic
hardship and disruption of veterinary and human public health
practices, such as occurs during war, there have been large
epidemics of anthrax. The largest reported epidemic of human
anthrax occurred in Zimbabwe from 1978 through 1980, with an
estimated 10,000 cases. Essentially all were cutaneous, with
very rare cases of gastrointestinal disease and eight cases of
inhalational anthrax, although no autopsy confirmation was reported7.
__________________
1. Wilson GS, Miles AA. Topley and Wilson’s Principles of
Bacteriology and Immunity. Vol 2. Baltimore, Md: Williams & Wilkins;
1955: 1940
2. Glassman HN. World incidence of anthrax in man. Public
Health Rep. 1958;73:22–24.
3. Fujikura T. Current occurrence of anthrax in man and
animals. Salisbury Med Bull Suppl. 1990;68:1.
4. Brachman PS. Inhalation anthrax. Ann N Y Acad Sci.
1980;353:83–93.
5. Elkina AV. The epidemiology of a pulmonary form of
anthrax. Zh Mikrobiol Epidemiol Immunobiol. 1971;48:112–116.
6. Plotkin SA, Brachman PS, Utell M, Bumford FH, Atchison
MM. An epidemic of inhalation anthrax, the first in the twentieth
century, I: Clinical features. Am J Med. 1960;29:992–1001.
7. Davies JC. A major epidemic of anthrax in Zimbabwe. Cent
Afr J Med (Zimbabwe).
(The preceding material was derived from the Virtual Naval
Hospital web site www.vnh.org)
[to top]
|
|
|
