Anthrax is caused by Bacillus anthracis. The spores of these Gram-positive bacilli are extremely hardy and withstand extremes of temperature and humidity. The organism is capable of toxin production and this property correlates most closely with its virulence. The disease occurs world-wide. Epidemics have been reported in The Gambia, in both North and South America and in southern Europe. Transmission is through direct contact with an infected animal; infection is most frequently seen in farmers, butchers, and dealers in wool and animal hides. Spores can also be ingested or inhaled. There have been cases in the USA due to the deliberate release of anthrax spores as a bioterrorist weapon.
EPIDEMIOLOGY & DEMOGRAPHICS
• Anthrax most commonly occurs in hoofed animals and can only incidentally infect humans who come in contact with infected animals or animal products. Between 20,000 and 100,000 cases of cutaneous anthrax occur worldwide annually. In the U.S. the annual incidence was about 130 cases before 2001.
• Until the recent bioterrorism attack in 2001, most cases of anthrax occurred in industrial environments (contaminated raw materials used in manufacturing process) or in agriculture.
• In 2001 there were more than 20 confirmed cases of anthrax resulting from bioterrorism, most of which were associated with handling of contaminated mail. Inhalation anthrax is the most lethal form of anthrax and results from inspiration of 8000-50,000 spores of Bacillus anthracis. Before 2001 there had not been a case of inhalation anthrax in the U.S. for 20 years.
• Direct person-to-person spread of anthrax is extremely unlikely, if it occurs at all; therefore, there is no need to immunize or treat contacts of persons ill with anthrax, such as household contacts, friends, or co-workers, unless they also were exposed to the same source of infection.
• Inhalation anthrax begins with a brief prodrome resembling a viral respiratory illness followed by development of hypoxia and dyspnea, with radiographic evidence of mediastinal widening. Host factors, dose of exposure, and chemoprophylaxis may affect the duration of the incubation period. Initial symptoms include mild fever, muscle aches, and malaise and may progress to respiratory failure and shock; meningitis often develops.
• Cutaneous anthrax is characterized by a skin lesion evolving from a papule, through a vesicular stage, to a depressed black eschar. The incubation period ranges from 1-12 days. The lesion is usually painless, but patients also may have fever, malaise, headache, and regional lymphadenopathy. The eschar dries and falls off in 1-2 wk with little scarring.
• Gastrointestinal anthrax is characterized by severe abdominal pain followed by fever and signs of septicemia. Bloody diarrhea and signs of acute abdomen may occur. This form of anthrax usually follows after eating raw or undercooked contaminated meat and can have an incubation period of 1-7 days. Gastric ulcers may occur and may be associated with hematemesis. An oropharyngeal and an abdominal form of the disease have been described. Involvement of the pharynx is usually characterized by lesions at the base of the tongue, dysphagia, fever, and regional lymphadenopathy. Lower bowel inflammation typically causes nausea, loss of appetite, and fever followed by abdominal pain, hematemesis, and bloody diarrhea.
The disease is caused by Bacillus anthracis, a gram-positive, spore-forming bacillus. It is aerobic, nonmotile, nonhemolytic on sheep’s blood agar, and grows readily at temperature of 37° C, forming large colonies with irregularly tapered outgrowths (a Medusa’s head appearance). In the host it appears as single organisms or chains of two or three bacilli.
The diagnosis is established by demonstrating the organism in smears from cutaneous lesions or by culture of blood and other body fluids. Serological confirmation can be made using ELISAs detecting antibodies to both the organism and a toxin.
• Inhalation anthrax must be distinguished from influenza-like illness (ILI) and tularemia. Most cases of ILI are associated with nasal congestion and rhinorrhea,
which are unusual in inhalation anthrax. Additional distinguishing factors are the usual absence of abnormal chest x-ray in ILI (see below).
• Cutaneous anthrax should be distinguished from staphylococcal disease, ecthyma, ecthyma gangrenosum, plague, brown recluse spider bite, and tularemia.
• The differential diagnosis of gastrointestinal anthrax includes viral gastroenteritis, shigellosis, and yersiniosis.
• Presumptive identification is based on Gram stain of material from skin lesion, CSF, or blood showing encapsulated gram-positive bacilli.
• Confirmatory tests are performed at specialized labs. Virulent strains grow on nutrient agar in the presence of 5% CO2 . Susceptibility to lysis by gamma phage or DFA staining of cell-wall polysaccharide antigen are also useful confirmatory tests.
• Nasal swab culture to determine inhalation exposure are of limited diagnostic value. A negative result does not exclude the possibility of exposure. It may be used by public health officials to assist in epidemiologic investigations of exposed persons to evaluate the dispersion of spores.
• Serologic testing by enzyme-linked immunosorbent assay (ELISA) can confirm the diagnosis.
• A skin test (Anthracin Test) that detects anthrax cell-mediated immunity is also available in specialized labs.
Chest x-ray usually reveals mediastinal widening. Additional findings include infiltrates and pleural effusion.
IV hydration and ventilator support may be necessary in inhalation anthrax
ACUTE GENERAL THERAPY
• Most naturally occurring B. anthracis strains are sensitive to penicillin. The FDA has approved penicillin, doxycycline, and ciprofloxacin for the treatment of inhalational anthrax infection.
• Table 1-11 describes a treatment protocol for inhalation anthrax.
• The treatment protocol for cutaneous anthrax is described in Table 1-12.
• Initial postexposure prophylaxis therapy in adults is with ciprofloxacin, 500 mg PO bid or doxycycline 100 mg bid. The total duration of treatment is 60 days.
• Case fatality estimates for inhalation anthrax are extremely high (>90%).
• The case fatality rate for cutaneous anthrax is 20% without and <1% with antibiotic treatment.
• The case fatality rate for gastrointestinal anthrax is estimated to be 25% to 60%.
PHYSICAL FINDINGS & CLINICAL PRESENTATION
Symptoms of disease vary depending on how the disease was contracted, but usually occur within 7 days after exposure. The serious forms of human anthrax are inhalation anthrax, cutaneous anthrax, and intestinal anthrax.
The incubation period is 1-10 days. Cutaneous anthrax is the most common. The small, erythematous, maculopapular lesion is initially painless. It may subsequently vesiculate and ulcerate, with formation of a central black eschar. The illness is self-limiting in the majority of patients, but occasionally perivesicular oedema and regional lymphadenopathy may be marked, and toxaemia can occur.
Inhalational anthrax (woolsorter’s disease) follows inhalation of spores, and bioterrorism should be suspected. A febrile illness is accompanied by non-productive cough and retrosternal discomfort; pleural effusions are common. Untreated, the mortality is about 90%, and in the cases in the USA it was 45% despite treatment.
Gastrointestinal anthrax is due to consumption of undercooked, contaminated meat. It presents as severe gastroenteritis; haematemesis and bloody diarrhoea can occur. Toxaemia, shock and death may follow.