Bacillus Species (Including Anthrax)

Epidemiology

B. anthracis, a large, gram-positive, encapsulated, spore-forming, nonmotile rod, is the cause of anthrax. Anthrax, a disease of herbivores that acquire B. anthracis while grazing in areas where soil is contaminated by spores, is a zoonotic disease of worldwide occurrence. Disease tends to occur in animals in summer and fall ; insects can serve as vectors. Humans typically become infected as they contact infected domestic or wild animals or their products. B. anthracis spores can survive for prolonged periods, thus permitting relapsing infection. Human infections have resulted from contact with contaminated products, such as hides, wool, bone meal, animal-hair shaving brushes, imported dolls, drums, and toys. Injectional anthrax, associated with use of contaminated heroin, has also been described. The largest outbreak of injectional anthrax included 119 heroin users in Scotland, with 13 fatal cases (3 attributed to anthrax meningitis). Discharge from cutaneous lesions is potentially infectious, and person-to-person transmission is possible. The incubation period is 1–7 days but can be up to 60 days depending on host factors, exposure dose, and chemoprophylaxis.

Naturally occurring human disease is rarely reported in the US. Before the bioterrorism-related anthrax outbreak of 2001, only 18 cases of inhalational anthrax had been reported in the US in the 20th century. A series of US cases involved exposure to imported animal hides associated with drumming or drum making. ^{, ,} In 2015, 22 US military personnel were unintentionally exposed to B. anthracis inactivated spores in South Korea; no clinical cases were reported after receiving post-exposure prophylaxis.

Clinical Manifestations

Three forms of human disease occur:

• 1.

  Cutaneous anthrax accounts for most anthrax seen in the US and worldwide; infection follows inoculation of existing skin lesions with B. anthracis spores. A painless lesion evolves from a pruritic papule (malignant papule) to a vesicular lesion over 2–6 days and eventually forms an eschar (see Fig. 68.7 ). Striking local edema occurs as a result of release of extracellular toxin, and regional lymphadenopathy and lymphangitis also are noted. Compartment syndrome due to significant edema has been reported. Although antibiotic treatment does not alter the progression of an anthrax lesion itself, the mortality rate approaches 20% in patients with untreated cases.

• 2.

  Inhalational anthrax (wool sorters’ disease) results from inhalation of aerosolized spores. A biphasic disease, when it occurs naturally, begins with mild upper respiratory tract symptoms that progress to dyspnea, cyanosis, tachycardia, fever, hypoxemia, shock, and usually death. Bacteremia and hemorrhagic meningitis are common. The chest radiograph typically shows a widened mediastinum consistent with massive lymphadenopathy. This finding in a previously healthy patient with evidence of overwhelming flu-like illness is essentially pathognomonic of advanced inhalation anthrax; pleural effusions also are common. The mortality rate is reported to approach 90% ; the case-fatality rate among people who received intensive care in the 2001 attacks was 45%. The first case of naturally acquired inhalation anthrax in the US since 1976 was reported in 2006 in a man who made African drums from imported animal hides. A 2011 inhalational anthrax case with an undefined source involved a 61-year-old man following a vacation and represented only the third naturally acquired case reported in the US since 1976.

• 3.

  Gastrointestinal disease is a result of ingestion of contaminated, undercooked meat, with deposition of spores in the lower gastrointestinal tract. Disease manifests as abdominal pain and distention, with vomiting and diarrhea, followed by ascites, hemorrhagic lymphadenitis, and septicemia. Ulcerations can occur in the gastrointestinal mucosa and may result in hemorrhage; however, bowel perforation is uncommon. An anthrax case involving the gastrointestinal form of disease was reported following animal-hide drum exposure. The mortality rate is 40% or less. Oropharyngeal anthrax can follow upper gastrointestinal mucous membrane infection acquired from consumption of contaminated meat and manifests as lesions at the base of the tongue or tonsils, dysphagia, profound swelling of the neck, lymphadenopathy, and systemic symptoms. ^,

All forms of anthrax can progress to septicemia and meningitis, poor prognostic indicators. A 4-item assessment tool (severe headache, altered mental status, meningeal signs and other neurological deficits) for screening patients with systemic anthrax for meningitis during an anthrax mass casualty incident has been developed.

Intentional delivery of B. anthracis spores through the US mail in 2001 led to 22 cases of anthrax: 11 cases of inhalational and 11 cases of cutaneous anthrax. The patients with inhalational cases likely had direct exposure to a B. anthracis– containing envelope. Five patients exhibiting fulminant signs of inhalational illness at presentation died; 6 who came to medical attention less ill received combination antibiotic therapy active against B. anthracis and aggressive supportive care and survived. This ∼55% overall survival rate is higher than that in previous reports. Fever, chills, fatigue, malaise, and lethargy with minimal or nonproductive cough and nausea or vomiting were common symptoms. Profuse sweating was a prominent feature. No initial chest radiograph was normal, and pleural effusions were common.

Multiple cases of anthrax have been reported in children, including meningitis, hemorrhagic meningoencephalitis, periorbital cellulitis, neonatal septicemia and meningitis, oropharyngeal anthrax, intestinal anthrax, and cutaneous anthrax. ^{, , , ,} Clinical signs and symptoms in children are nonspecific and variable; the mortality rate is high. ^, During the 2001 US Postal Service anthrax outbreak, a 7-month-old infant developed cutaneous anthrax with microangiopathic hemolytic anemia; anthrax spores were identified at his mother’s out-of-home office.