Anthrax
What is Anthrax?
Anthrax is an acute infectious disease caused by a spore-forming gram-positive, rod-shaped
bacteria known as Bacillus anthracis. Anthrax is a rare and fatal zoonotic disease (animal to human
transmission) that can be found naturally in soil and usually affects wild and domestic animals
around the world.
The term anthrakis means coal in Greek, and the disease is named after the black appearance of
its cutaneous form.
Contact with anthrax can cause severe illness in both humans and animals.
Pathophysiology
Anthrax is primarily a disease of herbivores (eg, cattle, sheep, goats, horses).
Bacillus anthracis is a large, spore-forming, gram-positive rod.
Persistence of spores is aided by nitrogen and organic soil content, environmental pH greater
than 6, and ambient temperature greater than 15°C.
Spores can exist indefinitely in the environment; optimal growth conditions result in a vegetative
phase and bacterial multiplication.
Drought or rainfall can trigger anthrax spore germination, while flies and vultures spread the
spores.
Anthrax toxins are composed of 3 entities: a protective antigen, a lethal factor, and
an edema factor.
The protective antigen is an 83-kd protein that binds to cell receptors within a target tissue.
The binding of edema factor at this site results in the formation of edema toxin; the binding of
lethal factor results in the formation of lethal toxin.
Humans are relatively resistant to cutaneous invasion by B anthracis, but the organisms may gain
access through microscopic or gross breaks in the skin.
The organisms multiply locally and may spread to the bloodstream or other organs (eg, spleen)
via the efferent lymphatics.
Primary intestinal anthrax predominantly affects the cecum and produces a local lesion similar to
the lesion produced in the cutaneous form.
, Inhaled spores are ingested by pulmonary macrophages and then carried to hilar and
mediastinal lymph nodes.
Anthrax in the lungs does not cause pneumonia, but it does cause hemorrhagic mediastinitis and
pulmonary edema.
Causes
Anthrax is caused by Bacillus anthracis, a gram-positive bacillus.
Working with infected animals or animal products. Most people who get sick from anthrax are
exposed while working with infected animals or animal products such as wool, hides, or hair.
Eating raw or undercooked meat from infected animals. People who eat raw or undercooked
meat from infected animals may get infected with gastrointestinal anthrax; this usually occurs in
countries where livestock are not routinely vaccinated against anthrax and food animals are not
inspected prior to slaughter.
Injecting heroin. A newly discovered type of anthrax is injection anthrax; this type of anthrax has
been seen in northern Europe in people injecting heroin.
Types
The type of illness a person develops depends on how anthrax enters the body; typically, anthrax
gets into the body through the skin, lungs, or gastrointestinal system.
Cutaneous anthrax. Cutaneous anthrax is the most common form of anthrax infection, and it is
also considered to be the least dangerous; cutaneous anthrax is most common on the head, neck,
forearms, and hands; infection usually develops from 1 to 7 days after exposure.
Inhalation anthrax. Inhalation anthrax is considered to be the most deadly form of anthrax;
infection usually develops within a week after exposure, but it can take up to 2 months; without
treatment, only about 10-15% of patients with inhalation anthrax survive.
Gastrointestinal anthrax. Gastrointestinal anthrax has rarely been reported in the United States;
infection usually develops from 1 to 7 days after exposure; once ingested, anthrax spores can
affect the upper gastrointestinal tract, stomach, and intestines.
Injection anthrax. Injection anthrax can spread throughout the body faster and be harder to
recognize and treat; symptoms may be similar to those of cutaneous anthrax, but there may be
infection deep under the skin or in the muscle where the drug was injected.
Statistics and Incidences
Natural incidence is rare, but infection is an occupational hazard among veterinarians, farmers, and
individuals who handle animal wool, hair, hides, or bone meal products.
From 1955–1994, US cases totaled 235, with 224 cases of cutaneous anthrax, 11 cases of
inhalational anthrax, and 20 fatalities.
In October 2001, 22 confirmed or suspected cases of anthrax infection were identified.
Cases were reported from Florida, New York, New Jersey, the District of Columbia, and
Connecticut.
, There were 11 confirmed cases of inhalational anthrax (5 deaths) and 7 confirmed and 4
suspected cases of cutaneous anthrax (no deaths).
Anthrax is uncommon in Western Europe, but the disease is not uncommon in the Middle East,
the Indian subcontinent, Africa, Asia, and Latin America.
Anthrax is endemic in Africa and Asia despite vaccination programs.
Clinical Manifestations
The symptoms of anthrax depend on the type of infection and can take anywhere from 1 day to
more than 2 months to appear.
Cutaneous symptoms. A group of small blisters or bumps that may itch, swelling that occurs
around the sore, and a painless skin sore or ulcer with a black center that appears after the small
blisters or bumps.
Inhalation symptoms. Inhalation anthrax symptoms can include fever and chills, chest
discomfort, shortness of breath, confusion or dizziness, cough, nausea and vomiting or stomach
pains, headache, sweats, extreme tiredness, and body aches.
Gastrointestinal symptoms. Gastrointestinal symptoms include painful swallowing, hoarseness,
nausea and bloody vomiting, diarrhea, stomach pain, and swelling of abdomen.
Injection symptoms. Injection anthrax symptoms include fever and chills, a small group of
blisters or bumps that may itch, appearing where the drug was injected, a painless skin sore with
a black center, swelling around the sore, and abscesses deep under the skin or in the muscle
where the drug was injected.
Assessment and Diagnostic Findings
Bacillus anthracis is present in high numbers in the ulcer/eschar of cutaneous anthrax, in bloody
pleural fluid in inhalational anthrax, in the cerebrospinal fluid (CSF) in anthrax meningitis, and in
the blood in septicemic anthrax.
Gram stain and blood culture. The preferred diagnostic procedure for cutaneous anthrax is
staining the ulcer exudate with methylene blue or Giemsa stain; B anthracis readily grows on
blood agar, and staining microbiologically differentiates the organism from non–B anthracis
bacilli.
Enzyme-linked immunosorbent assay (ELISA). Enzyme-linked immunosorbent assay (ELISA)
serologic diagnosis is also available; the ELISA for edema and lethal toxins is positive if a single
acute-phase titer is highly elevated or if a fourfold greater rise in the titer is observed between
acute and convalescent specimens.
Chest radiography and computed tomography. If inhalational anthrax is suspected, obtain a
chest radiograph or computed tomography (CT) scan; the appearance on chest radiograph or CT
scan may suggest the diagnosis, especially if other predisposing disorders that might result in a
widening mediastinum (eg, dissecting aortic aneurysm, bacterial mediastinitis) are absent.
Lumbar puncture. If anthrax meningitis is suspected, perform a lumbar puncture to obtain CSF
for stain and culture.
, Histologic findings. The characteristic finding in anthrax is the presence of the organisms in the
capillaries at the infection site; therefore, if a patient is infected, expect B anthracis in the
capillaries of the skin, intestines, liver, spleen, lungs, or leptomeninges.
Medical Management
There are several options to treat patients with anthrax; however, patients with serious cases may
require aggressive treatment.
Treatment for cutaneous anthrax. Patients with isolated cutaneous anthrax without systemic
involvement (ie, without edema, fever, cough, headache, etc) or complications may be treated on
an outpatient basis with antibiotic monotherapy.
Prehospital care. Persons who are potentially contaminated should wash with soap and water,
not bleach solutions; clothing and evidence/materials should be placed in plastic bags (triple); if
the contamination is confirmed, then a 1:10 dilution of household beach may be used to
decontaminate any materials and surfaces not sufficiently cleaned by soap and water.
Emergency department care. The emergency department workup includes rapid initiation of
intravenous antibiotic therapy; patients can be admitted to a normal hospital room with barrier
nursing procedures (ie, gown, gloves, mask) and secretion precautions (ie, special handing of
potentially infectious dressings, drainage, and excretions).
Consultations. Anthrax is a reportable disease; notify local health care authorities and the Centers
for Disease Control and Prevention of suspected cases; in addition, consultation with an infectious
disease specialist may be warranted, although treatment of patients in whom anthrax is suspected
is straightforward.
Deterrence and prevention. For PEP in adults, the CDC recommends vaccination and the use of
oral fluoroquinolones (ciprofloxacin, 500 mg bid; levofloxacin, 500 mg qd; or ofloxacin, 400 mg
bid); a vaccine exists but is not readily available; preexposure vaccination is recommended only
for populations at high risk of exposure to aerosolized B anthracis spores, according to the CDC’s
Advisory Committee on Immunization Practices (ACIP).
Pharmacologic Management
Pharmacologic treatment of Anthrax include:
Other antibiotics. Empirical antimicrobial therapy must be comprehensive and should cover all
likely pathogens in the context of the clinical setting.
Corticosteroids. These agents are used for severe edema, meningitis, or swelling in the head and
neck region.
Other antidotes. A monoclonal antibody (raxibacumab) and human anthrax immune globulin
have been approved by the FDA using the animal efficacy rule for inhalational anthrax.
Vaccines. The FDA approved a standard anthrax vaccine designated “anthrax vaccine adsorbed”
(AVA), which is a sterile filtrate of cultures of an avirulent strain that elaborates protective antigen;
no human controlled trials are available; it is the first vaccine approved utilizing the animal rule by
the FDA; the efficacy of this vaccine in inhalation (biowarfare) anthrax is questionable.
What is Anthrax?
Anthrax is an acute infectious disease caused by a spore-forming gram-positive, rod-shaped
bacteria known as Bacillus anthracis. Anthrax is a rare and fatal zoonotic disease (animal to human
transmission) that can be found naturally in soil and usually affects wild and domestic animals
around the world.
The term anthrakis means coal in Greek, and the disease is named after the black appearance of
its cutaneous form.
Contact with anthrax can cause severe illness in both humans and animals.
Pathophysiology
Anthrax is primarily a disease of herbivores (eg, cattle, sheep, goats, horses).
Bacillus anthracis is a large, spore-forming, gram-positive rod.
Persistence of spores is aided by nitrogen and organic soil content, environmental pH greater
than 6, and ambient temperature greater than 15°C.
Spores can exist indefinitely in the environment; optimal growth conditions result in a vegetative
phase and bacterial multiplication.
Drought or rainfall can trigger anthrax spore germination, while flies and vultures spread the
spores.
Anthrax toxins are composed of 3 entities: a protective antigen, a lethal factor, and
an edema factor.
The protective antigen is an 83-kd protein that binds to cell receptors within a target tissue.
The binding of edema factor at this site results in the formation of edema toxin; the binding of
lethal factor results in the formation of lethal toxin.
Humans are relatively resistant to cutaneous invasion by B anthracis, but the organisms may gain
access through microscopic or gross breaks in the skin.
The organisms multiply locally and may spread to the bloodstream or other organs (eg, spleen)
via the efferent lymphatics.
Primary intestinal anthrax predominantly affects the cecum and produces a local lesion similar to
the lesion produced in the cutaneous form.
, Inhaled spores are ingested by pulmonary macrophages and then carried to hilar and
mediastinal lymph nodes.
Anthrax in the lungs does not cause pneumonia, but it does cause hemorrhagic mediastinitis and
pulmonary edema.
Causes
Anthrax is caused by Bacillus anthracis, a gram-positive bacillus.
Working with infected animals or animal products. Most people who get sick from anthrax are
exposed while working with infected animals or animal products such as wool, hides, or hair.
Eating raw or undercooked meat from infected animals. People who eat raw or undercooked
meat from infected animals may get infected with gastrointestinal anthrax; this usually occurs in
countries where livestock are not routinely vaccinated against anthrax and food animals are not
inspected prior to slaughter.
Injecting heroin. A newly discovered type of anthrax is injection anthrax; this type of anthrax has
been seen in northern Europe in people injecting heroin.
Types
The type of illness a person develops depends on how anthrax enters the body; typically, anthrax
gets into the body through the skin, lungs, or gastrointestinal system.
Cutaneous anthrax. Cutaneous anthrax is the most common form of anthrax infection, and it is
also considered to be the least dangerous; cutaneous anthrax is most common on the head, neck,
forearms, and hands; infection usually develops from 1 to 7 days after exposure.
Inhalation anthrax. Inhalation anthrax is considered to be the most deadly form of anthrax;
infection usually develops within a week after exposure, but it can take up to 2 months; without
treatment, only about 10-15% of patients with inhalation anthrax survive.
Gastrointestinal anthrax. Gastrointestinal anthrax has rarely been reported in the United States;
infection usually develops from 1 to 7 days after exposure; once ingested, anthrax spores can
affect the upper gastrointestinal tract, stomach, and intestines.
Injection anthrax. Injection anthrax can spread throughout the body faster and be harder to
recognize and treat; symptoms may be similar to those of cutaneous anthrax, but there may be
infection deep under the skin or in the muscle where the drug was injected.
Statistics and Incidences
Natural incidence is rare, but infection is an occupational hazard among veterinarians, farmers, and
individuals who handle animal wool, hair, hides, or bone meal products.
From 1955–1994, US cases totaled 235, with 224 cases of cutaneous anthrax, 11 cases of
inhalational anthrax, and 20 fatalities.
In October 2001, 22 confirmed or suspected cases of anthrax infection were identified.
Cases were reported from Florida, New York, New Jersey, the District of Columbia, and
Connecticut.
, There were 11 confirmed cases of inhalational anthrax (5 deaths) and 7 confirmed and 4
suspected cases of cutaneous anthrax (no deaths).
Anthrax is uncommon in Western Europe, but the disease is not uncommon in the Middle East,
the Indian subcontinent, Africa, Asia, and Latin America.
Anthrax is endemic in Africa and Asia despite vaccination programs.
Clinical Manifestations
The symptoms of anthrax depend on the type of infection and can take anywhere from 1 day to
more than 2 months to appear.
Cutaneous symptoms. A group of small blisters or bumps that may itch, swelling that occurs
around the sore, and a painless skin sore or ulcer with a black center that appears after the small
blisters or bumps.
Inhalation symptoms. Inhalation anthrax symptoms can include fever and chills, chest
discomfort, shortness of breath, confusion or dizziness, cough, nausea and vomiting or stomach
pains, headache, sweats, extreme tiredness, and body aches.
Gastrointestinal symptoms. Gastrointestinal symptoms include painful swallowing, hoarseness,
nausea and bloody vomiting, diarrhea, stomach pain, and swelling of abdomen.
Injection symptoms. Injection anthrax symptoms include fever and chills, a small group of
blisters or bumps that may itch, appearing where the drug was injected, a painless skin sore with
a black center, swelling around the sore, and abscesses deep under the skin or in the muscle
where the drug was injected.
Assessment and Diagnostic Findings
Bacillus anthracis is present in high numbers in the ulcer/eschar of cutaneous anthrax, in bloody
pleural fluid in inhalational anthrax, in the cerebrospinal fluid (CSF) in anthrax meningitis, and in
the blood in septicemic anthrax.
Gram stain and blood culture. The preferred diagnostic procedure for cutaneous anthrax is
staining the ulcer exudate with methylene blue or Giemsa stain; B anthracis readily grows on
blood agar, and staining microbiologically differentiates the organism from non–B anthracis
bacilli.
Enzyme-linked immunosorbent assay (ELISA). Enzyme-linked immunosorbent assay (ELISA)
serologic diagnosis is also available; the ELISA for edema and lethal toxins is positive if a single
acute-phase titer is highly elevated or if a fourfold greater rise in the titer is observed between
acute and convalescent specimens.
Chest radiography and computed tomography. If inhalational anthrax is suspected, obtain a
chest radiograph or computed tomography (CT) scan; the appearance on chest radiograph or CT
scan may suggest the diagnosis, especially if other predisposing disorders that might result in a
widening mediastinum (eg, dissecting aortic aneurysm, bacterial mediastinitis) are absent.
Lumbar puncture. If anthrax meningitis is suspected, perform a lumbar puncture to obtain CSF
for stain and culture.
, Histologic findings. The characteristic finding in anthrax is the presence of the organisms in the
capillaries at the infection site; therefore, if a patient is infected, expect B anthracis in the
capillaries of the skin, intestines, liver, spleen, lungs, or leptomeninges.
Medical Management
There are several options to treat patients with anthrax; however, patients with serious cases may
require aggressive treatment.
Treatment for cutaneous anthrax. Patients with isolated cutaneous anthrax without systemic
involvement (ie, without edema, fever, cough, headache, etc) or complications may be treated on
an outpatient basis with antibiotic monotherapy.
Prehospital care. Persons who are potentially contaminated should wash with soap and water,
not bleach solutions; clothing and evidence/materials should be placed in plastic bags (triple); if
the contamination is confirmed, then a 1:10 dilution of household beach may be used to
decontaminate any materials and surfaces not sufficiently cleaned by soap and water.
Emergency department care. The emergency department workup includes rapid initiation of
intravenous antibiotic therapy; patients can be admitted to a normal hospital room with barrier
nursing procedures (ie, gown, gloves, mask) and secretion precautions (ie, special handing of
potentially infectious dressings, drainage, and excretions).
Consultations. Anthrax is a reportable disease; notify local health care authorities and the Centers
for Disease Control and Prevention of suspected cases; in addition, consultation with an infectious
disease specialist may be warranted, although treatment of patients in whom anthrax is suspected
is straightforward.
Deterrence and prevention. For PEP in adults, the CDC recommends vaccination and the use of
oral fluoroquinolones (ciprofloxacin, 500 mg bid; levofloxacin, 500 mg qd; or ofloxacin, 400 mg
bid); a vaccine exists but is not readily available; preexposure vaccination is recommended only
for populations at high risk of exposure to aerosolized B anthracis spores, according to the CDC’s
Advisory Committee on Immunization Practices (ACIP).
Pharmacologic Management
Pharmacologic treatment of Anthrax include:
Other antibiotics. Empirical antimicrobial therapy must be comprehensive and should cover all
likely pathogens in the context of the clinical setting.
Corticosteroids. These agents are used for severe edema, meningitis, or swelling in the head and
neck region.
Other antidotes. A monoclonal antibody (raxibacumab) and human anthrax immune globulin
have been approved by the FDA using the animal efficacy rule for inhalational anthrax.
Vaccines. The FDA approved a standard anthrax vaccine designated “anthrax vaccine adsorbed”
(AVA), which is a sterile filtrate of cultures of an avirulent strain that elaborates protective antigen;
no human controlled trials are available; it is the first vaccine approved utilizing the animal rule by
the FDA; the efficacy of this vaccine in inhalation (biowarfare) anthrax is questionable.
