The Centers for Disease Control and Prevention (CDC) stratified potential bioweapons into three levels of risk (Tables 213-1, 213-2 and 213-3) based on ease of manufacture, ease of dissemination, subsequent person-to-person transmission, lethality, and psychosocial effects (literally, how terrified a community will be). When an organism is intentionally dispersed as part of warfare, terrorism, or criminal activity, a goal is to infect huge numbers of people. Hence, the dispersal system may be engineered to disseminate the disease widely, often as airborne spread that results in pulmonary or inhalational disease. Some—but not all—of the pathogens are then transmissible from person to person, thereby potentiating the public health effects of—and the terror associated with—biologic weapons.
Category A Agents and Diseases
(See Chapter 183.) In late 2001, an outbreak of 22 cases in several states along the Eastern Seaboard of the United States was due to an intentional, criminal act of bioterrorism.10,11 The outbreak occurred when envelopes of spores were distributed through the postal system, contaminating many offices and infecting mail handlers and letter recipients. Initially, it was thought the anthrax spores were finely engineered into an easily aerosolized form, but more recent examinations suggest that even crudely milled spores can cause such an outbreak. The Federal Bureau of Investigation now believes that the perpetrator was a scientist working at the US Army's infectious disease laboratory at Fort Detrick, MD. The motive, however, remains unknown.
The Easy Weaponization of This Highly Lethal Agent Makes it One of the Most Feared Biologic Weapons
During the Cold War, several nations were known to have produced massive quantities of weaponized anthrax, evidence of which became widely known after a 1979 mishap at the Soviet Union's Sverdlosk bioweapon facility. A cloud of anthrax spores was accidentally released and dozens of people downwind died from inhalational anthrax. The Sverdlosk disaster, however, led to the notion that weaponized anthrax caused only inhalational illness. The letter-borne anthrax incidents of late 2001 showed otherwise when only 11 of the 22 victims had inhalational disease, four of whom died. The others had cutaneous anthrax.
The infectious propagule of Bacillus anthracis is its spore, not the activated bacillus. Under harsh environmental conditions, anthrax bacilli revert into spores that can remain dormant in soil or animal products for decades, impervious to heat, cold, desiccation, and solar radiation. These hardy spores are 1–2 μm in diameter and are easily introduced into open skin, aerosolized and inhaled, or ingested. Once in the hospitable environment of human tissue, the spores germinate, transforming into activated bacilli (2.5 × 10 μm) that generate disease-causing toxins but pose no risk of further direct human-to-human contagion.12
When spores enter the body, they are ingested by host macrophages where they transform into activated bacilli. These macrophages may be carried to regional lymphnodes and produce a hemorrhagic lymphadenitis. If bacteremia ensues, septicemia with shock and often meningitis may follow. The activated bacilli produce exotoxins and virulence factors. A pair of toxins, designated edema toxin and lethal toxin, consists of a pair of noncovalently linked protein components4: edema toxin consists of edema factor (EF) plus protective antigen (PA); lethal toxin consists of lethal factor (LF) plus PA. PA binds to a surface receptor on most mammalian cells and is subsequently cleaved by furin-like proteases. LF is capable of killing macrophages or, at lower concentrations, inducing them to overproduce specific cytokines (TNF-α, interleukin-1β).4 These actions are probably responsible for the sudden death from toxicity that occurs with high concentrations of bacteremia (107–108 bacilli per milliliter of blood) and terminally high lethal toxin levels.13
Inhalational disease can have longer incubation periods than cutaneous disease, perhaps as long as 40–60 days. If a person is on antibiotics (for another reason or for anthrax prophylaxis), Bacillus anthracis may remain in its more protected spore form until the antibiotics are discontinued. The initial symptoms of inhalation anthrax are flu-like and nonspecific, characterized by fever, fatigue, and malaise, but soon followed by chills, high fever, nonproductive cough, and dyspnea. Cyanosis, shock, multiorgan failure, and death may ensue. Chest radiographs characteristically show symmetric mediastinal widening due to hemorrhagic lymphadenitis of mediastinal nodes. In inhalational disease, as well as in septicemic anthrax, which may follow cutaneous or gastrointestinal anthrax, bacteremia may lead to fulminant meningitis.10,11,14,15
Patients with inhalational anthrax often present initially with a flu-like illness that progresses virulently into severe febrile illness accompanied by tachypnea, stridor, and cyanosis. In inhalation anthrax, the chest X-ray shows significant mediastinal widening and hilar adenopathy because of edema and hemorrhagic necrosis of draining nodes. The pulmonary parenchyma is usually spared; hence, the disease is identified as inhalational anthrax, not pulmonary anthrax.12
The acute onset of a painless edematous noduloulcerative lesion with a black eschar should elicit the possible diagnosis of cutaneous anthrax, especially in the epidemiologic setting of exposure to imported animal products, recent travel to endemic areas, or presence of known use of weaponized anthrax (see Fig. 183-1 and eBox 213-0.1).16 An additional clinical clue is the presence of edema vastly out of proportion to the observed size of the cutaneous lesion. Diagnostic steps include obtaining swabs of exudates for Gram stain and culture, biopsy specimens for histopathology and immunohistochemical staining, and to draw blood samples for culture and serology. The CDC requests that practitioners notify local or state health departments before attempting a laboratory diagnosis of cutaneous anthrax.
eBox 213-0.1 Diagnostic Algorithm for Suspected Cutaneous Anthrax ||Download (.pdf)
eBox 213-0.1 Diagnostic Algorithm for Suspected Cutaneous Anthrax
- The highest suspicion should be given to those lesions in which the patient had a known or highly suspected exposure to anthrax. However, as some of the recent cases have demonstrated, no known exposure had occurred when the patients presented for care.
- Notify your local Department of Health to inform them of the patient with suspected anthrax and to obtain any additional instructions before doing diagnostic tests. (A list of state Department of Health contacts can be found at http://www.cdc.gov/phppo by clicking on “State Public Health Locator”). Notify your local laboratory regarding suspected anthrax, and inform them that samples will be sent shortly.
- Diagnosis: Physicians should maintain universal precautions when evaluating patients with suspected cutaneous anthrax (mask is not required). Although contact with exudate should be avoided (as should contact with any blood or body fluid), physicians evaluating patients with suspected cutaneous anthrax are not considered at risk for contracting inhalational anthrax because the disease is acquired through contact with anthrax spores, not active bacteria. The laboratory evaluation should include the following:
- Swab exudates for Gram stain and culture. The organism is best demonstrated when lesions are in the vesicular stage. If vesicles are present, soak two, dry, sterile Dacron- or Rayon- (not cotton) tipped swabs in vesicular fluid from a previously unopened vesicle. During the eschar stage, gently lift an edge of the eschar and rotate two swabs beneath the edge without removing the eschar. If neither vesicle nor eschar is present, swab the base of the ulcer with a sterile, moist, synthetic (Dacron or Rayon) swab. (Lesions usually become sterile within 24–48 hours after starting antibiotics effective against Bacillus anthracis. Therefore, culture of lesions in patients on antibiotics may not yield bacterial growth.)
- Obtain a full-thickness (through the entire dermis), 4-mm punch biopsy for permanent sections (formalin-fixed) for histologic evaluation, IHC studies, and PCR. A second sterile punch biopsy specimen can be obtained for Gram stain and bacterial culture and fungal and atypical mycobacterial stains and cultures if indicated (bacterial Culturette or sterile nonbacteriostatic saline). Dividing a single biopsy specimen is not recommended.
- If a vesicle is present, biopsy the edge of the vesicle and include adjacent nonvesicular skin.
- If an eschar is present, biopsy the erythematous area immediately adjacent to the edge of the eschar. If possible, a second biopsy from the center of the eschar is useful.
- If both a vesicle and eschar are present, a biopsy of each lesion is indicated.
- Submitted specimens should be accompanied by information such as brief clinical history, description, and chronology of the lesion(s), treatment, and date of biopsy in relation to antibiotic treatment. A photograph, digital image, or diagram indicating the site of each biopsy in relation to the lesion and descriptive details of the lesion would be extremely valuable.
- The sample for permanent sections should be placed in formalin and shipped at room temperature. After preparing hematoxylin and eosin-stained slides,a the fixed tissue block should be saved by the dermatopathology laboratory for potential transfer to the CDC for histologic evaluation, IHC, and PCR.
- The sample for culture should be transported immediately to the microbiology laboratory fresh in a sterile container or in a bacterial culture tube (e.g., a Culturette) for immediate processing for Gram stain and bacterial culture, and fungal and atypical mycobacterial stains and cultures if indicated. (One may add sterile nonbacteriostatic saline to the container.)
- Draw one 5-mL tube of blood into a red-topped or serum separator tube and transfer it to the laboratory for isolation of serum and subsequent storage of serum at −70°C (−94°F). Label the tube: “Anthrax serology. Store serum at −70°C for special pickup.” A similar convalescent sample should also be drawn 3–4 weeks later.
- Draw one 5-mL tube of blood into a purple-topped tube. This tube should be refrigerated and held for pick up for potential PCR diagnostic tests by the CDC. Blood-based assays are currently in a state of development by the CDC. During your contact with your local laboratory or Department of Health office, ask them about the up-to-date blood-testing recommendations.
- Obtain blood cultures for febrile or hospitalized patients. There is no need to perform nasal swabs unless directed by the public health authorities as part of an epidemiologic investigation.
The diagnosis is usually suspected on the basis of the character of the lesion and the occupational history, hobby exposure, or likelihood of bioterrorism. Demonstration of large Gram-positive rods in aspirated fluid from beneath the eschar, or on skin punch biopsy, also using a direct fluorescent antibody technique supports the diagnosis. Definitive diagnosis requires culture of the organism and demonstration of its susceptibility to specific bacteriophage lysis. Occasionally, the organism can be isolated from the blood during the acute cutaneous illness as well as in disseminated anthrax. Retrospective serodiagnosis is possible with the demonstration of a titer rise in electrophoretic immunotransblots of antibody to protective antigen and enzyme-linked immunosorbent assay for detection of antibodies to a particular toxin called lethal factor.
Acute staphylococcal cellulitis with a central pustular lesion or an abscess with a necrotic eschar, particularly those due to methicillin-resistant Staphylococcus aureus (MRSA), may be confused with early anthrax. The pyogenic infections, however, are usually very painful and tender, and the etiologic agent is usually present on Gram-stain examination. Differential diagnosis of cutaneous anthrax includes ecthyma (caused by Streptococcus pyogenes and usually without edema or systemic manifestations), ecthyma gangrenosum (usually in the setting of neutropenia and Pseudomonas aeruginosa bacteremia), orf (caused by a parapoxvirus through contact with sheep or goats; vesicopustular lesions without gelatinous edema), and a brown recluse spider bite (causes pain with incipient necrosis).
Naturally occurring anthrax is susceptible to penicillin and doxycycline but weaponized anthrax may have been engineered to be resistant to these antibiotics. Therefore, a fluoroquinolone such as ciprofloxacin is recommended for initial treatment of confirmed or suspected anthrax, even in pregnant women and children in whom this class of antibiotic is rarely administered. Once drug sensitivities have been established, the patient may be switched to another antibiotic as clinically indicated. Current treatment of cutaneous anthrax in adults in the setting of bioterrorism involves the use of ciprofloxacin (500 mg po bid) or doxycycline (100 mg po bid) for 60 days because possible coexposure to inhaled anthrax spores.10,11 Antibiotics kill activated B. anthracis bacilli but do not reverse the effects of toxins already produced. For that, one must use anthrax Immunoglobulin (AIG).
Two types of vaccine are available for immunization against anthrax.7 The first vaccine (anthrax vaccine adsorbed, AVA) is licensed for human use in the United States to protect workers in occupations that might expose them to B. anthracis. Since 1998, it has often been given to members of the Armed Forces of the United States. It can also be used as part of a postexposure prophylactic regimen. The vaccine is a sterile culture filtrate (composed primarily of protective antigen) of an attenuated strain of B. anthracis adsorbed to an aluminum hydroxide adjuvant and administered in five doses over 18 months. The second vaccine is for immunization of livestock against anthrax and consists of viable spores of an attenuated, nonencapsulated, toxigenic strain.
Another form of anthrax that can cause highly lethal outbreaks is gastrointestinal anthrax, although this is regarded as an unlikely route for intentional spread of anthrax spores. Gastrointestinal anthrax occurs after the ingestion of raw or undercooked meat-infected animals. Although vegetative bacteria are killed by gastric acid, the anthrax spores are resistant and are activated when in the caecum or colon. Gastrointestinal anthrax produces acute abdominal pain with distension and fever, often accompanied by hematemesis and bloody diarrhea. Unless there are other confirmed cases in a community, the diagnosis is rarely suspected, hence the high mortality rates, due to shock and secondary sepsis, with this form of anthrax. An uncommon oropharyngeal variant occurs if the spores activate and penetrate the oropharyngeal mucosa before entering the stomach. Because contaminated meat may be eaten by many people in a family or community, gastrointestinal anthrax usually presents in dramatic outbreaks, rather than as individual cases. The largest such outbreak is suspected to have occurred in 1770 in Haiti where perhaps 15,000 people died after consumption of uncooked beef during a time of civil upheaval.17 A case on gastrointestinal anthrax was reported in a New Hampshire woman in 2009. Presumably she inadvertently ingested anthrax spores that had been on the leather surface of a West African drum that she was playing.18
(See Chapter 183.) Plague is caused by Yersinia pestis, an aerobic Gram-negative bacillus with “safety-pin” bipolar staining (see Chapter 183). In nature, plague is usually limited to enzootic cycles between rodent reservoirs and flea vectors. Most human infections occur via fleabites and typically lead to bubonic plague, which is highly lethal but generally not communicable to others. In naturally occurring disease, human-to-human transmission occurs mainly if the patient's condition changes from bubonic form of plague to the pneumonic form. Once in the lungs, the pathogens are dispersed within droplets that others inhale, leading to additional cases of pneumonic plague. This form of plague is more deadly than bubonic, having a fatality rate among untreated cases that approaches 100%. Hence, deliberate spread of aerosolized plague bacteria could kill massive numbers of people.19,20
The Japanese military tested plague as a biological weapon during the occupation of Manchuria before and during World War II. Rather than spreading the bacteria via airborne routes, the Japanese allegedly distributed common fleas—Pulex irritans—that had been infected with Yersinia pestis.19
Pneumonic plague does not produce buboes, which are the result of transcutaneous transmission via fleabites. Instead, pneumonic plague produces skin lesions if it evolves into septicemic plague. Then the patient may develop acral ecchymoses and distal gangrene, often accompanied by disseminated intravascular coagulation. These lesions resemble purpura fulminans, septic emboli, or meningococcemic purpura, and possibly gave rise to the term Black Death.
Plague in any form is a reportable disease in every jurisdiction worldwide. Confirmatory laboratory tests include culture of Y. pestis from a clinical specimen or detection by polymerase chain reaction. Serologic tests are not useful in the acute setting.21
In the event of an outbreak of pneumonic plague, the keystone of protection is isolation of cases and the use of prophylactic antibiotics, specifically doxycycline, a quinolone such as ciprofloxacin, chloramphenicol, or cotrimoxazole. The human vaccine against plague has been withdrawn. For cases, the preferred regimen is parenteral gentamicin combined with oral (see Table 180-1).
(See Chapter 183.) Tularemia, like plague, ordinarily exists in enzootic cycles and infects humans most commonly after an arthropod bite. The usual arthropod vector to transmit tularemia is a tick (such as Dermacentor andersoni, D. variabilis, or Amblyomma americanum) and less commonly a deerfly, Chrysops discalis, or in Northern Europe, certain mosquitoes. Furthermore, like plague, tularemia occasionally presents in a pulmonary form, with the pathogens entering the lungs either through septicemic spread from a lymphocutaneous focus, or directly through the inhalation of aerosolized bacteria. The infectious inoculum for Francisella tularensis is extremely small, perhaps as few as 50 organisms.22,23 Because pneumonic tularemia is highly lethal, the intentional dispersal of airborne organisms has the potential to cause devastating outbreaks of disease. Unlike pneumonic plague, however, pulmonary tularemia cannot be spread from person to person.
Tularemia can be acquired through several routes and present in several clinical forms. Pulmonary tularemia, which presumably would be the main form seen after intentional airborne spread, lacks cutaneous lesions. Airborne spread could, however, lead to other forms of the disease, such as oculoglandular and gastrointestinal, which in some cases have mucocutaneous findings.
Tularemia is a reportable disease and any pulmonary case or cluster of other cases should launch an epidemiologic investigation. In the event of an outbreak of pneumonic tularemia, health authorities should consider community prophylaxis with doxycycline or ciprofloxacin. Streptomycin (or in its absence, gentamicin) treats all forms of tularemia successfully when administered early in the course of the disease. Clinical improvement is evident within 24–48 hours, but treatment should be continued for at least 7–10 afebrile days. Tetracycline and chloramphenicol are acceptable alternatives but should be given for longer periods than 21 and 14 days, respectively, to reduce the risk of relapse.23 In the United States, the National Institutes of Health and the Department of Defense are funding development of a newer vaccine.
For epidemiology, etiology, and pathogenesis, clinical manifestations, prognosis, and vaccination see Chapter 195.24–27
After the World Health Organization declared that naturally occurring smallpox was eradicated, laboratories worldwide destroyed their stocks of variola—except for a few facilities that maintained small amounts of virus, putatively for research purposes. With the collapse of the Soviet Union and the dismantling of its military medical research system, there have been concerns that rogue states or terrorist organizations have obtained unmonitored stocks of virus. Any recurrence of smallpox represents a catastrophic medical, public health, and criminal event of extraordinary proportions.
The differential diagnosis of smallpox and varicella is described in eBox 213-0.2.
eBox 213-0.2 Clinical Presentations of Classic Chickenpox and Smallpox ||Download (.pdf)
eBox 213-0.2 Clinical Presentations of Classic Chickenpox and Smallpox
- Mild or no prodrome
- Superficial vesicles
- “Dew drops on a rose petal”
- Individual lesions evolve rapidly
- Lesions with different morphologies
- Central predominance
- Spares palms and soles
- Patient is rarely toxic
- Febrile prodrome
- Deep pustules
- “Pearls of pus”
- Individual lesions evolve gradually
- Lesions with same morphology
- Acral predominance
- Involves palms and soles
- Patient is usually toxic or moribund
The CDC has an algorithm for the evaluation of suspected smallpox and offers a differential diagnosis. The algorithm, Evaluating patients for smallpox: acute, generalized vesicular or pustular rash illness protocol (available at http://www.bt.cdc.gov/agent/smallpox/diagnosis/pdf/spox-poster-full.pdf), identifies three features at the core of a clinical diagnosis of smallpox (Box 213-1).28
Box 213-1 Core Features in the Clinical Diagnosis of Suspected Smallpox ||Download (.pdf)
Box 213-1 Core Features in the Clinical Diagnosis of Suspected Smallpox
- Febrile prodrome occurring 1–4 days before rash onset with fever ≥38.3°C (101°F) and at least one of the following: prostration, headache, backache, chills, vomiting, or severe abdominal pain.
- Classic smallpox lesions are deep-seated, firm or hard, round, well-circumscribed vesicles or pustules that are sharply raised and feel like small, round objects embedded under the skin. As they evolve, the lesions may become umbilicated or confluent.
- Lesions in the same stage of development: On any one part of the body (e.g., face or arm), all lesions are in the same stage of development—that is, all are vesicles or all are pustules.
Dermatologists who serve as bioterrorism resources for their communities or hospitals must become familiar with smallpox vaccination programs. Vaccinia, an orthopoxvirus related to smallpox and to the cowpox originally used in Jenner inoculations, can produce several cutaneous adverse effects, which require some expertise to diagnose and manage. These conditions are reviewed in detail in Chapter 195.
Category B Agents and Diseases with Possible Cutaneous Manifestations
(See Chapter 183.) Brucellosis is a zoonotic infectious disease that is usually transmitted to humans by direct contact with infected animals or animal products or by ingestion of contaminated dairy products. It can also be transmitted via aerosolized propagules and requires a small inoculum, perhaps 10–100 organisms, to cause human disease. Hence, it is regarded as a possible biologic weapon. Indeed, during the Cold War, the United States and other nations allegedly experimented with the weaponization of Brucella suis.8,29,30
Deliberate spread of aerosolized bacteria would cause pulmonary disease, which has a mortality rate, even when untreated, of less than 5%. The disease can cause profound fatigue and requires prolonged treatment; hence, victims could be incapacitated for months. Subsequent human-to-human transmission will not occur. Cutaneous manifestations of brucellosis are uncommon and nonspecific and are discussed in detail in Chapter 183.
(See Chapter 183.) Melioidosis and glanders are clinically similar diseases caused by the related bacteria Burkholderia pseudomallei and Burkholderia mallei, respectively. The clinical presentations of the two illnesses are similar but the pathogens have markedly different environmental niches. Glanders naturally occurs in horses, donkeys, mules, and other equids—although it is extremely rare worldwide today. Melioidosis is found in fresh water and damp soils in tropical regions, notably Southeast Asia, particularly Singapore and northeast Thailand, and in the coastal areas of northern Australia.31,32
As biologic weapons, these organisms would be disseminated in aerosols to cause respiratory outbreaks. Only a small inoculum of either is required to cause illness. The incubation period is roughly 10–14 days, and the subsequent pulmonary disease has a mortality rate of more than 95% untreated or approximately 40% when treated with appropriate antibiotics. Pulmonary disease can lead to bacteremia or septicemia, which can produce cutaneous and subcutaneous abscesses (see Chapter 183).32–34
The first case of human glanders in the United States in more than 50 years was reported in 2002 in a microbiologist who was inadvertently exposed at an Army Research Laboratory. He developed axillary lymphadenopathy and bacteremic infection with hepatic and splenic abscesses but responded well to prolonged treatment with imipenem and doxycycline.35
Category C is an expanding list of diseases, mostly caused by emerging pathogens that could possibly be engineered for mass dissemination and major public health impact.9 The number of diseases in Category C continues to expand as new diseases, such as severe acute respiratory syndrome, avian flu (caused by the H5N1 strain of influenza A virus), and Nipah virus infection are recognized for their potential for high morbidity, mortality, and societal disruption.9
Most diseases currently in Category C lack specific dermatologic findings. In nature, many are arthropod-borne viral hemorrhagic fevers that present with the systemic effects of vascular compromise, widespread hemorrhage, and hypovolemic shock. These conditions are often accompanied by cutaneous manifestations of thrombocytopenia and hemorrhage, namely petechiae, purpura, and frank bleeding from orifices and mucosal surfaces. The most severe of these, Crimean–Congo hemorrhagic fever caused by a bunyavirus, is usually transmitted by hard ticks in the genus Hyalomma. Several other pathogens, such as yellow fever virus, are transmitted by mosquitoes. If—or when—used for bioterrorism, Category C pathogens will likely be transmitted by aerosolization, contamination of drinking or food supplies, or in ways yet to be engineered.