|
Volume CXXXIII, Number 7 |
 |
Anthrax: what you need to know
ANNE McBRIDE
STAFF WRITER
In 1905 a former country doctor named Robert Koch won the
Nobel Prize in Medicine for his work that proved that the bacterium Bacillus
anthracis caused anthrax. The small, free-living cell Koch saw through
his microscope has generated much interest in this country over the past
few weeks with its appearance in congressional, postal, and media workers.
There are several pressing issues about anthrax, including what we know
about the bacterium, how it is spread, and the tools we have to fight
this invisible enemy.
The bacterium and the disease
Unlike E. coli and Salmonella, two common bacteria that
can cause human disease, B. anthracis belongs to one of only two families
of medically relevant bacteria that can produce spores. This resilient
dormant form of the bacterium is surrounded by a thick wall, which makes
it highly resistant to heat, lack of water, many chemicals, and radiation.
Spores can survive in the soil for decades and are primarily
responsible for the occasional anthrax cases found among grazing farm
animals. When spores enter the body, they can develop into a rapidly growing
bacterial form. These bacteria then produce toxic proteins that cause
disease in the host animal.
Historically, human anthrax cases have been limited to people who work
with farm animals or animal products, such as wool or hides. The most
dangerous form of anthrax, often called "woolsorter's disease,"
is contracted through inhalation of spores. Workers can also contract
cutaneous, or skin, anthrax if they have open wounds that come in contact
with either infected animals or bacteria in the soil. A very rare form
of anthrax has been seen in people who have eaten meat contaminated with
anthrax bacteria.
How can the bacterium's site of entry into the body affect
the severity of anthrax? The environment deep inside the lung is favorable
for growth of the bacterium. The release of toxins and the spread of the
bacteria to neighboring areas and the bloodstream leads to fatal disease.
The body, however, has developed numerous defenses to keep invading organisms
from reaching this vulnerable part of the lung, from hairs in the nostrils
to mucus in the upper respiratory tract.
The inhaled form of anthrax thus requires two conditions.
First, the spores must be delivered as a fine powder so that they can
slip past the body's defenses. Second, 8,000 to 10,000 spores must be
inhaled to lead to disease. Both of these points present obstacles to
potential bioterrorists: "milling" anthrax to a form of powder
and distributing the powder to infect many individuals are not trivial
tasks. In addition, anthrax does not appear to be contagious and therefore
is unlikely to increase the number of victims of an anthrax attack.
The arsenal against anthrax
Since anthrax is caused by a bacterium rather than a virus,
a variety of antibiotic drugs can be used to fight the disease. Penicillin,
the first antibiotic to come into common use after World War II, is effective
against naturally occurring strains of the anthrax bacterium. However,
penicillin-resistant strains are readily selected in the laboratory. Therefore,
ciprofloxacin, marketed as "Cipro," is recommended for treatment
of people who have been exposed to likely laboratory strains of anthrax.
Other antibiotics related to Cipro are also suggested as possible alternatives.
Antibiotic treatment needs to begin as soon as possible
after exposure to the bacterium, preferably before the initial flu-like
symptoms arise, which can take 1-6 days in the case of inhaled anthrax.
Nasal swabs allow the detection of anthrax spores in people who may have
breathed in powdered anthrax. Prompt treatment is crucial because damage
to the patient is caused by the accumulation of bacterial toxins, and
these toxins continue to act after all bacteria have been killed.
Vaccination is a complementary approach to antibiotic use
in fighting many bacterial diseases. In the 1880's, at the dawn of the
age of vaccination, Louis Pasteur developed a vaccine that prevented anthrax
in animals. Rather than attacking the bacterium directly, vaccination
acts by priming the immune system. When an animal is vaccinated against
anthrax and then is exposed to the bacterium, the animal's immune system
is ready to mount a swift and intense campaign against the invader. Humans
need three initial doses of the anthrax vaccine and yearly boosters for
effective protection against future infection.
Protecting public health: present and future
Although the increasing number of anthrax cases around the
nation is alarming, our response both as individuals and as a community
needs to be measured with an eye on the future of fighting infectious
diseases. People need to remain alert to suspicious mail, unknown powders
and possible symptoms of anthrax, and to seek help if these signs are
detected.
In the absence of such signs, however, being overly cautious
by taking antibiotics or flooding health facilities for anthrax tests
could lead to serious consequences. The former could facilitate the development
of antibiotic resistance in bacteria other than anthrax. The latter could
overwhelm the health care system such that actual cases cannot be treated
as quickly as necessary to allow survival.
We have the knowledge and the tools to handle anthrax outbreaks.
Now strengthening the public health systems in this country and around
the world will be crucial in the continuing battle against microscopic
enemies.
For more on anthrax see: The Bowdoin College Anthrax Threat
Guidelines:
http://www.bowdoin.edu/news/guidelines.shtml.
Centers for Disease Control and Prevention website: http://www.bt.cdc.gov/Agent/Anthrax/Anthrax.asp.
"Clinical and Epidemiological Principles of Anthrax" by Theodore
J. Cieslak and Edward M. Eitzen, Jr. in Emerging Infectious Diseases (Special
issue, Vol. 5, No. 4, 2001) http://www.cdc.gov/ncidod/eid/vol5no4/cieslak.htm