Environmental Engineering Reference
In-Depth Information
infected animal meat or hides. Anthrax spores gain entry through skin abrasions
or cuts. In fact, the term
anthrax
derives from the Greek word for “coal” and
reflects the blackened nature of advanced skin lesions produced by infected
individuals. It is far less fatal (under 1 percent) than the gastrointestinal and
pulmonary form, which may exceed 50 percent. Gastrointestinal anthrax results
from the ingestion of spores and if the disease reaches the septicemia stage,
fatality rates are as high as 90 percent. Pulmonary anthrax, while normally rare,
poses the greatest risk to humans that have inhaled the spores. Initiating the dis-
ease requires a high infectious dose, however, the incubation period is short (on
the order of two days) followed by rapidly progressing symptoms culminating
in cardiovascular arrest. Fortunately,
B. anthracis
responds readily to antibiotic
therapy, most notably, penicillin. Antibiotics such as amoxicillin, ciprofloxacin,
and doxycycline are effective against the inhalation form of anthrax; however,
they must be administered prior to spore germination, which can occur
within 48 to 72 hours following exposure and must be continued for several
months.
The level of naturally occurring, human anthrax in the United States is nearly
nil, having fallen steadily from about 130 cases in 1920. The last reported inci-
dence of naturally occurring anthrax was a cutaneous case in 1989; however, in
2006, a pulmonary case developed in New York City.
As already noted, anthrax poses a major concern for use in bioterrorism. The
endospore stage of the organism confers longevity for the organisms in the envi-
ronment and represents an advantage to its use as a bioweapon. In fact, it is
believed that during World War I, Germany intentionally infected sheep to be
shipped to Russia for the purpose of infecting the Russian military. Gastrointesti-
nal anthrax has been reported in the former Soviet Union, but never in the United
States. Inhalation of anthrax spores, resulting in the full-blown pulmonary dis-
ease, is highly fatal when untreated — and sometimes even with treatment. Of the
18 cases of pulmonary anthrax recorded in the United States for the entire twen-
tieth century, greater than 75 percent of them were fatal. The anthrax bacillus
synthesizes four major virulence factors: a antiphagocytic polysaccharide cap-
sule and three separate proteins (exotoxins) that act to induce an endema in the
infected localities of the body and cause macrophages to elicit tumor necrosis
factor and interleukin 1, which promotes sudden death in the pulmonary disease.
An anthrax vaccine is available and is generally effective, although it is currently
in limited supply (and mostly dedicated to military rather than civilian use). It
has also been observed to cause side effects. Animal vaccines are available, also,
however, disease incidence in herds has been so meager that farmers are reluctant
to have their animals vaccinated.
It will be important to be able to rapidly monitor and analyze the genetic
properties of different anthrax strains and to develop new antibiotics. Another
promising avenue stems from the recent identification of the receptor for anthrax
lethal factor toxin
110
as well as high-resolution structural determination of lethal
factor
111
and edema factor.
112
These molecules represent potential targets for
rational drug design of new antibacterial compounds to combat this disease.
