Introduction
Biological weapons are agents, including bacteria, viruses, fungi, and toxins, used for malicious purposes: in war (biowarfare), to cause terror (bioterrorism), or for criminal acts (biocrime). [Suspected Intentional Use Of Biologic And Toxic Agents. 2018] Some agents are lethal, and others cause illness or incapacitation. Entities direct biological agents at the human population, crops, and livestock. More than 180 pathogens and biotoxins have been researched or employed as biological weapons, including those that cause anthrax, tularemia, brucellosis, plague, Legionnaire disease, Q fever, glanders, melioidosis, smallpox, viral hemorrhagic fevers, influenza, coccidiosis, rice blast, and wheat rust. Biotoxins include ricin, botulinum toxin, and staphylococcal enterotoxin B. Designers create biological weapons to disperse as aerosols, facilitating rapid spread across large populations. However, agents may also spread from person to person or by vectors, ingestion, direct contact, or other methods.
Agents used for biological weapons have distinct advantages over conventional agents (eg, chemical weapons):
Microbial agents are often more easily mass-produced
Large quantities are easy to conceal and transport
Agents are more easily able to become airborne or waterborne, increasing the area of dissemination
Some agents pass from person to person
Classification
Biological agents are classified into different categories depending on their ability to cause illness and their impact on public health. The United States Centers for Disease Control and Prevention (CDC) categorizes agents into 3 groups:[1]
Category A
Highest priority
Easily disseminated or transmitted
High mortality rates and potential for major public health impact
Can cause public panic and social disruption
Require specific actions for public health preparedness
Category B
Second highest priority
Moderately easy to disseminate
Moderate morbidity and low mortality
Require specific enhancements to the CDC's diagnostic and disease surveillance capacities
Category C
Category A agents include Bacillus anthracis (anthrax), Clostridium botulinum toxin (botulism), Yersinia pestis (plague), Variola major (smallpox), Francisella tularensis (tularemia), and viruses that cause hemorrhagic fevers (eg, Ebola virus, Marburg virus, Lassa virus). Category B agents include Brucella species (Brucellosis), Chlamydia psittaci (Psittacosis), Coxiella burnetii (Q fever), ricin toxin (from Ricinus communis), enteric pathogens (Salmonella, Escherichia coli O157:H7, Shigella), Staphylococcal enterotoxin B, and viruses that cause encephalitis. Category C agents are emerging pathogens such as Nipah virus and hantavirus.[1]
Clinical Significance
Anthrax
Anthrax infection can occur due to environmental or animal exposure (eg, "woolsorter disease") or to bioterrorism. Bacillus anthracis is a zoonotic, gram-positive, rod-shaped bacteria existing in the environment as an endospore. Infection occurs when spores germinate in host macrophages; as few as 2500 spores may cause infection. Four clinical forms exist based on the portal of entry: cutaneous, gastrointestinal, inhalational, and injectional.[9][10] Mortalities are estimated to be 1%, 25% to 60%, 46%, and 33%, respectively.[10] B anthracis causes gastrointestinal and inhalational anthrax infection when used as a bioweapon.
Gastrointestinal anthrax results from ingesting spore-contaminated meat, with an incubation period of 1 to 6 days.[11] Gastrointestinal anthrax has oropharyngeal and intestinal forms. Oropharyngeal infection results from spores settling in the pharyngeal area, resulting in localized ulceration, fever, and neck swelling. In intestinal anthrax, infection results in ulcerations in the small intestine, mesenteric lymphadenopathy, and ascites, possibly leading to bowel obstruction and perforation.[11] Both types of gastrointestinal anthrax are typically complicated by shock.
After an incubation period of about 4 days, the clinical course of inhalational anthrax is biphasic, first presenting as flu-like symptoms lasting about 4 days.[10] Without treatment, patients can rapidly deteriorate with respiratory distress, refractory shock, and death within 24 hours. A classic diagnostic finding is hemorrhagic mediastinitis, seen as a widened mediastinum on chest radiography.[10]
A case is confirmed as anthrax by a compatible clinical picture with at least 2 supportive tests such as culture, serology, and real-time polymerase chain reaction (PCR). Standard barrier and contact precautions for patients with draining lesions are adequate, as anthrax does not spread from person to person.[12] As a nationally notifiable disease, it must be reported to public health officials. Infected human and animal remains should be burned.[12]
The resilience of the spores to killing and the general ease of laboratory growth make anthrax a dangerous biological weapon.[13] Strains of weaponized anthrax may be penicillin-resistant.
Treat patients with suspected, possible, or confirmed meningitis due to anthrax with multiple antibiotics: a fluoroquinolone (eg, ciprofloxacin) plus a B-lactam (eg, meropenem) or penicillin as bactericidal agents, plus a protein synthesis inhibitor (eg, Linezolid).[14][12] Once meningitis is excluded, antibiotics can be adjusted. Postexposure prophylaxis (PEP) consists of 42 to 60 days of oral ciprofloxacin or doxycycline plus 3 doses of subcutaneous anthrax vaccine absorbed (AVA) at 0, 2, and 4 weeks.[14][12] PEP can be started at diagnosis of illness if not given previously.
Plague
Yersinia pestis, a gram-negative, aerobic, non-spore-forming coccobacillus, causes the plague. The plague has been responsible for multiple pandemics and epidemics, notably killing over 25 million people in 14th-century Europe during the "black death."[15] Plague is usually transmitted from rodent reservoirs to humans by the bite of flea vectors. Yersinia pestis was used as a biological weapon in World War II when the Imperial Japanese dropped plague-contaminated rice and fleas into Chuhsien, China, resulting in an outbreak.[15]
Plague presents in 3 clinical variants.
Bubonic plague is the most common. Patients develop fevers, abdominal pain, and headaches. The rapid proliferation of bacteria in lymph nodes causes painful "buboes" in the groin, axillary, and cervical regions. Bubonic plague can develop into pneumonic or septicemic plague if not recognized and treated in time.
Pneumonic plague presents a nonspecific flu-like illness that progresses to severe hemoptysis and respiratory distress.
[16] This is the only form of plague that can spread from person to person via aerosolized droplets.
In septicemic plague, patients develop
Yersinia pestis bacteremia, disseminated intravascular coagulation, and gangrene of the extremities.
[17]
The incubation period may be as long as 6 days or less than 1 day if a large quantity of Y pestis is inhaled; however, the average period is 2 to 3 days.[16] Mortality ranges from 40% in bubonic plague to nearly 100% in septicemic and pneumonic plague without treatment.[18]
Plague should be suspected when a compatible epidemiological and clinical picture presents; confirmation is via at least 2 positive tests such as culture, PCR, or serum antibody detection performed in a level 3 or higher laboratory.[16] Patients with Y pestis infection require contact and droplet precautions. Streptomycin, ciprofloxacin,[19] doxycycline, and chloramphenicol can effectively treat plague.[20][18][21][22] Plague is notifiable to public health officials.
Brucellosis
Brucella species, ubiquitous gram-negative coccobacilli, cause brucellosis infections. Brucella is usually transmitted to humans from infected animals by contact or by consuming undercooked meat or unpasteurized dairy products. Person-to-person spread is rare; transmission through sexual contact and breastfeeding has been reported. Brucella are easily aerosolized, and few organisms are required to cause disease.
The incubation period of Brucellosis ranges from 5 days to 5 months.[Brucellosis - Patients with Suspected Infection. 2012] Brucellosis begins as a flu-like illness, with headache, fever, and arthralgias. Patients can develop hepatomegaly, transaminitis, orchitis, epididymitis, endocarditis, and anemia. Symptoms can become chronic even with treatment. Neurobrucellosis occurs when meningitis or meningoencephalitis is present and is associated with optic neuritis, cerebellitis, ischemic strokes, myelitis, [23][24] and chronic peripheral neuropathy, radiculopathy, or cranial nerve palsies.[25] Death occurs in 2% of cases, with endocarditis being the most common cause.
Diagnose Brucellosis by blood or cerebrospinal fluid cultures and treat with doxycycline plus either rifampin or streptomycin; sulfamethoxazole/trimethoprim may be used instead of doxycycline in children.[26] Brucellosis must be reported to public health in all states and territories.[Brucellosis - Surveillance. 2021]
Tularemia
Tularemia is caused by Francisella tularensis, a gram-negative facultative, intracellular coccobacillus spread primarily by arthropod vectors such as ticks; person-to-person spread has not been reported.[27] The incubation period is typically 3 to 5 days, ranging from 1 to 21 days.[Tularemia - For Clinicians. 2022] The symptoms of tularemia include fever, headache, and fatigue, with others dependent on the route of exposure.
Aerosolization of F tularensis for malicious purposes can lead to pneumonic, oropharyngeal, ulceroglandular, and oculoglandular tularemia. Pneumonic tularemia is the most severe, resulting from inhalational exposure; patients have respiratory symptoms and chest pain and can develop pleural effusions and mediastinitis. Oropharyngeal tularemia results from ingesting infected food and causes pharyngitis, fever, and cervical lymphadenopathy. Ulceroglandular tularemia is the most common and results from infection via broken skin or a vector bite; patients develop skin lesions and lymphadenopathy. Oculoglandular disease results in severe conjunctivitis from the contact of the conjunctiva with contaminated hands, water, or animal bodily fluids.[27]
Diagnose tularemia with an appropriate history and positive serology. F tularensis is difficult to culture, requiring a specific medium, trained lab technicians, and a biosafety level 3 laboratory.[Tularemia - For Clinicians. 2022] Patients with suspected tularemia do not require isolation. Tularemia is a nationally reportable infectious disease.
The antibiotic agent of choice for treatment depends on the patient and the severity of the disease:[28][29][27]
Streptomycin and gentamicin: first-line for treating severe infections
Doxycycline and ciprofloxacin: used in mild to moderate disease
Gentamicin: the agent of choice in children
Azithromycin: used for treating pregnant patients
Ciprofloxacin or doxycycline can be used for postexposure prophylaxis; vaccination is not generally available in the United States.[Tularemia - For Clinicians. 2022]
Q Fever
Q fever is caused by Coxiella burnetii spread by ingestion, aerosolization, and tick vectors. C burnetti is easy to aerosolize and resistant to heat, drying, and many common disinfectants.[Q Fever - Information for Healthcare Providers. 2019] Fewer than 10 organisms can cause infection. Transmission from person to person may rarely occur via the blood-borne route.
After an incubation period of 2 to 3 weeks,[30] the symptoms of Q fever include fever, chills, malaise, sweating, arthralgia, myalgia, cough, pleurisy, nausea, vomiting, and diarrhea. Roughly half of all people infected with C Burnett are asymptomatic. Acute Q fever is usually incapacitating rather than lethal, but pneumonia or myocarditis can lead to death. A post-Q fever fatigue syndrome affects up to 20% of patients with acute Q fever.[Q Fever - Information for Healthcare Providers. 2019] Less than 5% of acute cases become chronic, most commonly presenting with endocarditis or osteomyelitis weeks to years after an acute infection.[30] This condition is fatal if not treated.
Q fever can be challenging to diagnose: the symptoms can be highly variable; serology can remain harmful for 7 to 15 days after onset of illness; and PCR is most sensitive within the first week, rapidly declining following appropriate antibiotic treatment.[Q Fever - Information for Healthcare Providers. 2019] treatment must often be based on a presumptive diagnosis with later confirmation by a 4-fold increase in antibody titers.[30] Acute Q fever is treated for 2 weeks with doxycycline, while chronic Q fever requires prolonged doxycycline plus hydroxychloroquine.[3][Q Fever - Information for Healthcare Providers. 2019]
Standard infection control procedures are adequate for patients with Q fever, except during aerosol-generating procedures. Q fever must be reported to local or state public health officials.
Burkholderia
Burkholderia mallei causes glanders, a disease primarily of horses. Humans contract the disease extremely rarely by inhalation or contact of the organism with mucosal surfaces or breaks in the skin.[Glanders. 2017] Localized infections appear 1 to 5 days at the contaminated site; dissemination occurs 1 to 4 weeks after infection.[Glanders. 2017] Symptoms include fever, chills, night sweats, lymphadenopathy, headache, myalgias, tachypnea, nausea, vomiting, and diarrhea. Disseminated infections are usually fatal within 7 to 10 days without treatment. Even with treatment, mortality remains as high as 50%.[Glanders. 2017] The recommended treatments for glanders are doxycycline, trimethoprim/sulfamethoxazole, and chloramphenicol.[31] Diagnosis is by isolation of B mallei.
Patients with glanders require airborne precautions. While glanders is not a nationally notifiable disease, any unusual or cluster of infectious diseases should be reported to state or public health officials. Glanders has previously been used as a biological weapon and could be used again.[Glanders. 2017]
Smallpox
Variola virus is a type of orthopoxvirus that causes smallpox. This disease was eradicated in 1980 thanks to a concerted worldwide vaccination campaign and is now officially restricted to labs in the United States and Russia; however, unsanctioned reserves likely exist.[32] Variola virus is an ideal biological weapon because it is easily aerosolized, highly infectious, and transmissible from person to person.
Smallpox is spread by airborne droplets or contact with body fluids. After an incubation period of 1 to 2 weeks, smallpox presents in 1 of 4 clinical forms: ordinary, modified, malignant, or hemorrhagic. Ordinary smallpox begins as a macular rash that progresses to pustules and then vesicles; lesions first present on the face and distal extremities and spread to the trunk. Unlike chickenpox, lesions in any part of the body progress simultaneously through the clinical stages.
The initial diagnosis is based on the clinical presentation using 3 major and 5 minor criteria.[Evaluating Patients for Smallpox: Acute, Generalized Vesicular or Pustular Rash Illness Protocol. 2016]
Febrile prodrome 1 to 4 days before the onset of rash with fever >101 °F (38.3 °C) and at least prostration, headache, backache, chills, vomiting, or severe abdominal pain
Classic smallpox lesions with deep-seated, firm, well-circumscribed vesicles or pustules
Lesions in the same stage of development on any one part of the body
Centrifugal distribution of lesions
First lesions on the oral mucosal surfaces, face, or forearms
Patient appears toxic
Slow evolution of lesions from macule to papule to vesicle
Lesions on palms and soles
Place patients suspected of having smallpox in airborne isolation. Immediately notify the Infection Prevention and Control team and the local or state health department. Real-time PCR testing is the preferred diagnostic test.[Smallpox - Specimen Collection and Transport Guidelines. 2017]
The overall mortality of smallpox is approximately 30% in unvaccinated individuals. Smallpox vaccination within 72 hours of exposure can prevent the disease; vaccination within 3 to 7 days will not prevent the disease but will limit symptoms.[33] Cidofovir is theorized to be a treatment for short-term prophylaxis against smallpox. Consult the CDC for treatment recommendations.
Ricin
Ricin is a naturally occurring protein of a class called toxalbumins found in the castor oil plant Ricinus communis seeds. Ricin is classified as a category B biological agent by the CDC. Exposure to ricin can occur via ingestion, inhalation, and subcutaneous and intravenous routes.
Ricin inactivates ribosomes and causes toxicity by inhibiting protein synthesis. Both the A and B protein chains are required to cause toxicity; once ricin enters the body, chain B allows chain A to enter cells. Chain A then inhibits the 28S subunit of the 60S ribosome, effectively inhibiting protein translation and production.[34]
The median lethal dose (LD50) of ricin toxin by inhalation in humans is 5 to 10 μg/kg. Symptoms of ricin toxicity include nausea, diarrhea, tachycardia, hypotension, and seizures. Depending on the route of exposure, onset may be immediate or delayed for a few hours. The diagnosis is made by clinical picture and finding the toxin in tissue samples by liquid chromatography-mass spectrometry or immunoassay. The treatment of ricin toxicity is supportive, as no antidote exists.[35][36] The poison control center, infection control practitioner, and local or state public health officials should immediately be contacted to ensure proper decontamination and to determine if a public health threat exists.[Ricin - Control Measures Overview for Responders and Clinicians. 2018]
Botulinum Toxin
Clostridium botulinum is a spore-forming, anaerobic, gram-positive bacteria that produces botulinum toxin, also known as botulinum neurotoxin or BoNT. BoNT is a category A biological agent. BoNT consists of a light and heavy chain; the heavy chain is responsible for transporting the light chain into the neuron, while the light chain contains the enzyme that cleaves target proteins. The 7 main BoNT serotypes, A through G, have multiple subtypes. Clinical symptoms are similar between the different serotypes. More recently discovered variants challenge botulinum nomenclature; BoNT/H resembles subtypes A and F and is alternately called BoNT/FA or BoNT/HA and has lower potency with a slower progression of clinical symptoms.[37]
BoNT functions by inhibiting the release of acetylcholine at the neuromuscular junction. Once taken up into the neuron, the light chain targets components of the SNARE (soluble N-ethylmaleimide-sensitive fusion factor attachment protein receptor) complex, which is responsible for vesicular trafficking and neurotransmitter release. Serotypes A, C, and E cleave SNAP-25 (synaptosomal-associated protein of 25-kDa), while serotypes B, D, F, and G cleave syntaxin. The cleavage of these proteins disrupts neurotransmitter release, and signals cannot be transmitted across neuronal synapses.[34]
BoNT exposure can occur via inhalation, ingestion, or parenteral routes. Botulism causes descending flaccid paralysis, initially affecting bulbar muscles, with progression to involve skeletal and respiratory muscles. Initial symptoms occur within a few to 36 hours of poisoning [34] and include dysphagia, blurry vision, and speech difficulties.[38] Death may occur due to respiratory arrest from paralysis of the respiratory muscles.[39] BoNT has an LD50 of 1 ng/kg in mice. When inhaled, the lethal dose in a 70 kg human is 0.7 to 0.9 ug or 70 ug if ingested.[40]
Clinical criteria are available to aid the diagnosis of botulism as this condition is commonly misdiagnosed as myasthenia gravis, Guillain-Barre syndrome, intoxication, or psychiatric conditions.[38] Administering botulism antitoxin as soon as possible and preferably within 24 hours of symptom onset is critical.[38] Antitoxin does not reverse paralysis but will prevent its progression. Treatment is otherwise supportive; prolonged mechanical ventilation may be necessary.[35]
Botulinum antitoxin can be obtained via contact with local state health departments and through the CDC via their hotline at 770-488-7100.
