Aerobic, gram-positive, encapsulated, spore-forming, nonmotile, nonhemolytic, rod-shaped bacterium Bacillus anthracis .
Worldwide, most B. anthracis is transmitted by direct contact with B. anthracis –infected animals, their carcasses, or contaminated products from infected animals. Such products include meat, hides, wool, or items made with those products, such as drum heads or wool clothing. Anthrax has a variety of presentations—cutaneous, gastrointestinal, injection, inhalation, and meningitis—and most are synonymous with their mode of transmission. The exception is meningitis, which may complicate any of the other types. It may also occur with no obvious portal of entry, in which case it is called primary anthrax meningitis.
Introducing spores through the skin can result in cutaneous anthrax; abrasion of the skin increases susceptibility. Eating meat from infected animals can result in gastrointestinal anthrax. Since 2000, injecting, and possibly smoking and snorting, heroin has been associated with B. anthracis soft-tissue infections in intravenous drug users in northern Europe. Inhaling spores aerosolized during work with contaminated materials such as hides or wool can result in inhalation anthrax.
Anthrax in humans is not generally considered to be contagious; person-to-person transmission of cutaneous anthrax has rarely been reported.
Anthrax is a zoonotic disease that primarily affects herbivores such as cattle, sheep, goats, antelope, and deer, which become infected by ingesting contaminated vegetation, water, or soil; humans are generally incidental hosts. Anthrax is most common in agricultural regions in Central and South America, sub-Saharan Africa, Central and Southwestern Asia, and Southern and Eastern Europe. Although outbreaks occur most years in livestock and wild herbivores in the United States and Canada, human anthrax is now rare in both of these countries.
Worldwide, the most commonly reported form (95%–99%) of anthrax in humans is cutaneous anthrax. Outbreaks of cutaneous and gastrointestinal anthrax have been associated with handling infected animals and butchering and consuming meat from those animals. Most of these outbreaks are reported from endemic areas of Asia and Africa.
A single case of travel-associated anthrax has been reported. In 2006, a case of cutaneous anthrax was reported in a woman who traveled with a small group of tourists to Namibia, Botswana, and South Africa. Although she had no direct contact with animals, another group member handled 1 or more animal carcasses and shortly afterward helped her clean an abrasion on her finger, which was later the site of the anthrax lesion.
Additional cases have occurred from playing or handling drums made with contaminated goat hides that were imported from anthrax-endemic countries. Although the risk of acquiring anthrax from these drums appears to be low, life-threatening or fatal disease is possible: cases of cutaneous (4), gastrointestinal (1), and inhalation (3) anthrax have been reported among people who have handled, played, or made drums or who have been in the same place as people participating in these activities.
Severe soft tissue infections, including cases with sepsis and systemic infection, have been reported in drug users in northern Europe and are suspected to be due to recreational use of heroin contaminated with B. anthracis spores. No associated cases have been identified in people who have not taken heroin. To date, no heroin has been found to be contaminated with B. anthracis spores.
Inhalation exposure was historically associated with the industrial processing of hides or wool (hence, “woolsorters’ disease”). However, in more recent decades it has also resulted from bioterrorism. Occasional anthrax cases have occurred in the United States and elsewhere in which the exposure source remains unidentified.
Cutaneous anthrax usually develops 1–7 days after exposure, but incubations as long as 17 days have been reported. Before antimicrobial therapy, almost a quarter of patients with cutaneous anthrax died. The case-fatality ratio is <2% with antimicrobial therapy. Cutaneous anthrax is characterized by localized itching followed by the development of a painless papule, which turns vesicular and enlarges, ulcerates, and develops into a depressed black eschar within 7–10 days of the initial lesion. The head, neck, forearms, and hands are the most commonly affected sites. Edema usually surrounds the lesion, sometimes with secondary vesicles, hyperemia, and regional lymphadenopathy. Patients may have malaise and headache; about a third are febrile.
Gastrointestinal anthrax usually develops 1–7 days after consumption of contaminated meat; however, incubations as long as 16 days have been reported. More than half of cases die if untreated; with treatment, the case-fatality ratio is <40%. There are 2 main types, oropharyngeal and intestinal. Fever and chills are usual with either. The oropharyngeal type is characterized by severe sore throat, difficulty swallowing, swelling of the neck, and regional lymphadenopathy; airway compromise can occur. Symptoms of the intestinal type include nausea, vomiting, and diarrhea, which may be bloody; marked ascites may develop. Shock and death may occur within 2–5 days of onset.
Cases of anthrax in injection drug users usually develop within 1–4 days of exposure; more than a quarter of the confirmed cases die. Cases present with severe soft tissue infection manifested by swelling, erythema, and excessive bruising at the injection site; pain may be less than would be anticipated for the degree of swelling. In approximately a third of cases, the localized symptoms are accompanied by signs of sepsis.
Inhalation anthrax usually develops within a week after exposure, but the incubation period may be prolonged (up to 2 months). Fatality ratios before 2001 were 90%; since then, they have been 45%. Initially, most patients have constitutional symptoms such as fever, chills, and fatigue, which may be accompanied by cough, making inhalation anthrax difficult to distinguish from influenza and community-acquired pneumonia. This is often described as the prodromal period. Over the next day or so, chest pain develops in about half of patients, and nonthoracic complaints such as nausea, vomiting, headache, and diaphoresis develop in approximately one-third. Upper respiratory tract symptoms occur in only a quarter of patients, and myalgias are rare. Altered mental status or shortness of breath generally brings patients to the attention of the medical establishment and heralds the fulminant phase of illness.
Anthrax meningitis may develop from hematogenous spread of any of the clinical forms of anthrax, or it may occur alone; half of all reported cases are sequelae of cutaneous anthrax. Although anthrax meningitis is usually fatal, survival is significantly more likely if the patient receives multiple antimicrobials that include a bactericidal agent.
Laboratory diagnosis depends on bacterial culture and isolation of B. anthracis ; detection of bacterial DNA, antigens, or toxins; or detection of a host immune response to B. anthracis . Anthrax lethal toxin can be detected in acute-phase serum, while serologic testing of host antibody responses requires acute- and convalescent-phase sera for diagnosis. Confirmatory testing, including isolate identification, antigen detection in tissues, or quantitative serology, should be performed in the United States by the state health department or Laboratory Response Network laboratories, or internationally by the relevant national reference laboratory. Guidelines for collecting and submitting clinical specimens for testing and algorithms for laboratory diagnosis can be found at www.cdc.gov/anthrax/lab-testing/index.html. Specimens for culture should be collected before initiating antimicrobial therapy. Anthrax is a nationally notifiable disease.
Diagnostic procedures for inhalation anthrax include thoracic imaging studies to detect a widened mediastinum or pleural effusion. Unless contraindicated, lumbar puncture should be performed to rule out meningitis in all patients with systemic illness.
Naturally occurring localized or uncomplicated cutaneous anthrax can be treated with 7–10 days of a single oral antimicrobial agent. First-line agents include ciprofloxacin or an equivalent fluoroquinolone or doxycycline; clindamycin is an alternative, as are penicillins if the isolate is penicillin susceptible.
Treatment recommendations for systemic disease are available at wwwnc.cdc.gov/eid/article/20/2/13-0687_intro. Additional recommendations to prevent or treat anthrax in pregnant, postpartum, and lactating women are available at wwwnc.cdc.gov/eid/article/20/2/13-0611_intro.
The CDC published updated recommendations in 2010 for preexposure use of anthrax vaccine and for postexposure management of previously unvaccinated people (www.cdc.gov/mmwr/preview/mmwrhtml/rr5906a1.htm). Vaccination against anthrax is not recommended for travelers.
To prevent anthrax, travelers should:
- Avoid direct or indirect contact with carcasses of animals in anthrax-endemic regions.
- Not eat meat from animals that were not inspected by health officials and found to be healthy at the time of slaughter.
- Not import animal products, trophies, or souvenirs from anthrax-endemic regions that are prohibited by either the CDC or the United States Department of Agriculture (USDA). A map of endemic areas can be found at www.cdc.gov/anthrax/specificgroups/travelers.html.
No tests are available to determine if animal products are free of contamination with B. anthracis spores. Additional information regarding import regulations may be found in the following references:
- Chapter 6, Taking Animals & Animal Products across International Borders
- USADA regulations at www.aphis.usda.gov/aphis/ourfocus/importexport
- World Organisation for Animal Health (OIE) Terrestrial Animal Health Code at www.oie.int/en/international-standard-setting/terrestrial-code/access-online
Animal-hide drum owners or players should report any unexplained fever or new skin lesions to their health care provider and describe any recent contact with animal-hide drums.
CDC website: www.cdc.gov/anthrax
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Kate Hendricks Walters, Rita M. Traxler, Chung K. Marston