B. anthracis is primarily transmitted by direct contact with B. anthracis–infected animals, their carcasses, or with contaminated products from infected animals. Such products include meat, hides, wool, or items made with those products, such as drums or wool clothing.
Anthrax normally presents in 3 forms: cutaneous, gastrointestinal, and inhalation. Introduction of the 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. Inhalation anthrax typically occurs when a person inhales spores aerosolized from work with contaminated materials, such as hides or wool, in a way that can aerosolize dust and spores. Inhalation exposure was historically associated with industrial processing of hides or wool, but it has also resulted from bioterrorism. Rare inhalation anthrax cases have occurred in the United States and elsewhere where no source of exposure was identified. Since 2000, a new form of anthrax has been reported occurring among injecting heroin users; however, smoking and snorting heroin have also been identified as possible exposure routes. 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. Anthrax is now rare in the United States and Canada; however, sporadic outbreaks occur every year in livestock and wild herbivores in these countries. The most commonly reported form (95%–99%) of anthrax in humans worldwide is cutaneous anthrax. Outbreaks of cutaneous and gastrointestinal anthrax have been associated with handling infected animals, and butchering and consuming meat from those animals. Such outbreaks are primarily reported from endemic areas in Asia and Africa. Travelers to endemic areas have acquired cutaneous anthrax through either direct or indirect contact with carcasses of animals that died from anthrax. Cases of cutaneous, gastrointestinal, and inhalation anthrax have been reported among people who have handled or played drums made with contaminated goat hides from countries endemic for anthrax or who have been present at events where those drums have been played. Anthrax cases have also been reported among people making drums from contaminated goat hides imported from countries endemic for anthrax, as well as members of their households exposed to environments contaminated by the drum-making process.
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 had not deliberately taken heroin. To date no heroin has been found to be contaminated with B. anthracis spores.
Cutaneous anthrax usually develops 1–7 days after exposure. The case-fatality ratio is as high as 20% if untreated, but typically is <1% 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 associated fever, malaise, and headache.
Gastrointestinal anthrax usually develops 1–7 days after consumption of contaminated meat and can present in either intestinal or oropharyngeal forms. Shock and death may occur within 2–5 days of onset; estimates of the case-fatality ratio for gastrointestinal anthrax are >50% if untreated, and <40% with treatment.
Inhalation anthrax usually develops within a week after exposure, but the incubation period may be prolonged (up to 2 months). Estimates for the case-fatality ratio are >85%; even with aggressive treatment, this ratio can be as high as 45%. Initial symptoms are nonspecific and may mimic those of influenza, including myalgia, fever, nonproductive cough, malaise, nausea, and vomiting; upper respiratory tract symptoms are rare. The patient’s condition dramatically worsens 2–3 days after symptom onset, with the development of severe respiratory distress, diaphoresis, cyanosis, and shock.
Cases of anthrax in injection drug users reportedly developed within 1–4 days of exposure in most cases for which a suspected exposure could be identified; the case-fatality ratio was >25% in confirmed cases. Cases presented with severe soft tissue infection with or without localized swelling or with symptoms of sepsis, disseminated infection, and toxemia.
Hemorrhagic meningitis may develop from hematogenous spread of any of the clinical forms of anthrax. Anthrax meningitis is nearly always fatal.
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.bt.cdc.gov/agent/anthrax/lab-testing. Specimens for culture should be collected before initiating antimicrobial therapy. Diagnostic procedures for inhalation anthrax include thoracic imaging studies to detect a widened mediastinum or pleural effusion.
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. Ciprofloxacin is recommended as the primary antimicrobial component of an initial multidrug regimen for treating all forms of systemic anthrax until antimicrobial susceptibility data are available; levofloxacin and moxifloxacin are equivalent alternatives to ciprofloxacin. Because of intrinsic resistance, neither cephalosporins nor trimethoprim-sulfamethoxazole should be used.
The CDC published updated recommendations in 2010 for preexposure use of anthrax vaccine and for postexposure management for previously unvaccinated people (www.cdc.gov/mmwr/preview/mmwrhtml/rr5906a1.htm). Vaccination against anthrax is not recommended for travelers and is not available for civilian travelers. Travelers should not have direct or indirect contact with carcasses of animals found in anthrax-endemic regions or eat meat from animals that were not inspected by health officials and found to be healthy at the time of slaughter.
The risk of acquiring anthrax from playing with or handling an animal hide drum is very low. Since 2006, 6 cases of anthrax (including all 3 forms: cutaneous, gastrointestinal, and inhalation) in the United States and United Kingdom have been associated with making animal-hide drums or participating in drumming workshops or events where animal-hide drums were played. Some of these cases were fatal. Travelers who wish to bring back animal hides from anthrax-endemic regions to make drums should strongly consider the health risks before importing the hides.
No tests are available to determine if animal products are free of contamination with B. anthracis spores. Animal-hide drum owners or players should report any unexplained fever or new skin lesions to their health care provider and describe their recent contact with animal-hide drums.
The importation of goat-hide souvenirs, such as goat-hide drums, from Haiti is prohibited by CDC (see Chapter 6, Taking Animals & Animal Products across International Borders). Importation of animal products, including processed or unprocessed cattle and goat hides, is regulated by the United States Department of Agriculture (USDA). Animal products, trophies, or souvenirs from anthrax-endemic regions must be accompanied by an international veterinary certificate stating that they were harvested from animals that were free of anthrax, or that they have been disinfected in accordance with international regulations, for them to be allowed to be imported into the United States. Cattle or goat hides that have been tanned, pickled in a solution of salt and mineral acid, or treated with lime are considered to pose less of a risk for infectious diseases and may be imported under certain conditions. For more information, consult the USDA website at www.aphis.usda.gov/import_export/animals/animal_import/animal_imports.shtml and the World Organisation for Animal Health (OIE) Terrestrial Animal Health Code at www.oie.int/en/international-standard-setting/terrestrial-code/access-online.
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