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Clinical
Features |
Human anthrax has three major clinical
forms depending on the route of infection: cutaneous, inhalation,
and gastrointestinal. Cutaneous anthrax begins as a pruritic
papule or vesicle that enlarges and erodes (1-2 days) leaving
a necrotic ulcer with subsequent formation of a central black
eschar; inhalation anthrax may begin as a prodrome of fever,
chills, nonproductive cough, chest pain, headache, myalgias,
and malaise, with more distinctive clinical hallmarks of hemorrhagic
mediastinal lymphadenitis, hemorrhagic pleural effusions,
bacteremia and toxemia resulting in severe dyspnea, hypoxia
and septic shock; gastrointestinal anthrax may result in pharyngeal
lesions with sore throat, dypshagia marked neck swelling and
regional lymphadenopathy, or intestinal infection characterized
by fever, severe abdominal pain, massive ascites, hematemesis,
and bloody diarrhea. As with any form of anthrax, hemorrhagic
meningitis can result from hematogenous spread of the organism
from the primary site. |
Etiologic
Agent |
Bacillus anthracis is an
encapsulated gram-positive, nonmotile, aerobic, spore-forming
bacterial rod with a spore size of approximately 1 µm
x 2 µm. The three virulence factors of B. anthracis
are edema toxin, lethal toxin, and an antiphagocytic capsular
antigen. The toxins are responsible for the primary clinical
manifestations of hemorrhage, edema, and necrosis. |
Incidence |
In the United States, incidence
of naturally-acquired anthrax is extremely rare (~ 1-2 cases
of cutaneous disease per year). Gastrointestinal anthrax is
rare, but may occur as explosive outbreaks associated with
ingestion of infected animals. Worldwide, the incidence is
unknown, though B. anthracis is present in most of
the world. Unreliable reporting makes it difficult to estimate
the true incidence of human anthrax worldwide. However, in
fall 2001, 22 cases of anthrax (11 inhalation, 11 cutaneous)
were identified in the United States following intentional
contamination of the mail. |
Sequelae |
If untreated, anthrax in all forms
can lead to septicemia, hemorrhagic meningitis, and death.
The case fatality ratio for patients with appropriately treated
cutaneous anthrax is usually <1%, but for inhalation or
gastrointestinal disease it can exceed 50%. Case-fatality
rates for inhalation anthrax are high, even with appropriate
antibiotics and supportive care. Among the eighteen cases
of inhalation anthrax in the United States during the twentieth
century, the overall case fatality was >75%. Following
the bioterrorist attack in fall 2001, the case-fatality rate
among patients with inhalation disease was 45% (5/11). The
case-fatality rate of gastrointestinal anthrax is unknown
but is estimated to be 25%-60%. |
Transmission |
For humans, the source of infection
in naturally-acquired disease is through contact with infected
livestock, wild animals, or contaminated animal products (including
carcasses, hides, hair, wool, meat, and bone meal). Person-to-person
transmission is extremely unlikely and only reported with
cutaneous anthrax where discharges from cutaneous lesions
are potentially infectious. |
Risk
Groups |
Cutaneous anthrax is the most common
manifestation of naturally-acquired infection with B. anthracis.
Inhalation (pulmonary) anthrax occurs in persons working in
certain occupations where spores may be aerosolized from contaminated
animal products, such as animal hair processing or through
intentional release. Occupational risk groups include those
coming into contact with livestock or products from livestock,
e.g., veterinarians, animal handlers, abattoir workers, and
laboratorians. |
Surveillance |
For both livestock and humans, anthrax
is a notifiable disease in the United States. |
Trends |
In the United States, the annual
incidence of naturally-occurring human anthrax declined from
estimated 130 cases annually in the early 1900's to <2
cases each in 2000, 2001, and 2002. The recent cases of anthrax
that occurred after B. anthracis spores were distributed
through the U.S. mail have further underscored the potential
dangers of this organism as a bioterrorism threat. In addition
to aerosolization, there is a theoretical health risk associated
with B. anthracis spores being introduced into food
products or water supplies. |
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December 2003
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