Anthrax

Anthrax (malignant carbuncle, Anthrax, Pustula Maligna, rag picker's disease, wool sorters' disease) is an acute saprozoonotic infectious disease with a predominantly contact mechanism of transmission of the pathogen. Most often it occurs in a benign cutaneous form, less often in a generalized form. It is considered a dangerous infection. The causative agent of anthrax is considered as a biological weapon of mass destruction (bioterrorism).

ICD-10 codes

• A22.0. Cutaneous anthrax.
• A22.1. Pulmonary anthrax.
• A22.2. Gastrointestinal anthrax.
• A22.7. Anthrax septicemia.
• A22.8. Other forms of anthrax.
• A22.9. Anthrax, unspecified.

What causes anthrax?

Anthrax is caused by Bacillus anthracis. It is a toxin-producing, encapsulated, facultative anaerobe. Anthrax, often fatal in animals, is transmitted to humans by contact with infected animals or their products. In humans, infection is usually through the skin. Airborne transmission is less common. Oropharyngeal, meningeal, and gastrointestinal infections are rare. Inhalation and gastrointestinal infections, the initial nonspecific symptoms are followed within a few days by acute systemic manifestations, shock, and often death. Empirical treatment is with ciprofloxacin and doxycycline. Vaccination against anthrax is available.

In developed countries, cases of anthrax have declined significantly. However, the possibility of using the pathogen as a potential biological weapon has increased concern about the pathogen.

The pathogen quickly forms spores when dried. The spores are stable and can remain viable for decades in the wool and hair of animals. When the spores enter an environment containing large amounts of amino acids and glucose, they begin to germinate and multiply rapidly. In humans, infection usually occurs through the skin, but cases of infection are possible when eating contaminated meat, particularly when there is a defect in the mucous membrane of the throat or intestine, which facilitates invasion. Inhalation of spores, especially in the presence of acute respiratory disease, can lead to inhalational anthrax (shepherd's disease), which often leads to death. Bacteremia can occur with any form of anthrax and almost always accompanies fatal cases.

After entering the body, the spores enter the macrophages, where they germinate. Together with the macrophages, the bacteria enter the lymph nodes, where they multiply. In inhalation anthrax, the spores are deposited in the alveolar spaces, where they are absorbed by macrophages, which usually leads to hemorrhagic mediastinitis. Gastrointestinal infection usually results from eating improperly cooked contaminated meat. Only cutaneous anthrax is contagious (contagiousness is moderate). Infection occurs through direct contact, through lice bites, and with secretions from affected skin.

The bacterium secretes several exotoxins, which are classified according to their virulence. The most important toxins are edema toxin and lethal toxin. The protective antigen binds to target cells and facilitates intracellular penetration of edema or lethal toxin. Edema toxin causes massive local edema. Lethal toxin triggers massive release of cytokines by macrophages, which in turn can lead to sudden death. Sudden death in anthrax occurs quite often.

Anthrax is a dangerous disease of animals. It can occur in goats, cattle, sheep and horses. Anthrax can also occur in wildlife such as armadillos, elephants and bison. The disease rarely occurs in humans, and mainly in countries that do not practice industrial and agricultural prevention to prevent human contact with diseased animals and their products. For military and bioterrorism purposes, the spores are prepared in a very fine powder form.

What are the symptoms of anthrax?

In most cases, anthrax symptoms appear 1-6 days after exposure, but for inhalation anthrax, the incubation period can be more than 6 weeks.

Cutaneous anthrax begins with the appearance of a painful, itchy, red-brown papule. The papule enlarges, and a zone of brownish erythema and circumscribed edema develops around it. Vesiculation and induration are also present. Central ulceration with serous-bloody exudation and the formation of a black eschar (malignant pustule) then occur. Local lymphadenopathy often occurs, sometimes accompanied by general malaise, myalgia, headache, fever, nausea, and vomiting.

The initial symptoms of inhalation anthrax are nonspecific and resemble influenza. Over the next few days, fever increases, acute respiratory distress syndrome develops, accompanied by cyanosis, shock, and coma. Acute hemorrhagic necrotizing lymphadenitis develops, spreading to adjacent mediastinal structures. Serous-hemorrhagic transudate, pulmonary edema, and pleural effusion appear. Typical bronchopneumonia does not develop. Hemorrhagic meningoencephalitis and gastrointestinal anthrax may develop.

Gastrointestinal anthrax ranges from asymptomatic to fatal. When spores are ingested, they can cause lesions anywhere from the mouth to the cecum. The released toxin causes hemorrhagic necrosis extending to the mesenteric lymph nodes. Fever, nausea, vomiting, abdominal pain, and bloody diarrhea are common. Intestinal necrosis and septicemia may develop, potentially leading to toxic death.

Oropharyngeal anthrax is a mucocutaneous lesion in the oral cavity. It is accompanied by sore throat, fever, adenopathy, and dysphagia. Airway obstruction may develop.

How is anthrax diagnosed?

An occupational history with carriers is important for the diagnosis of anthrax. Gram stain and culture should be performed from clinically identified lesions; skin, pleural fluid, cerebrospinal fluid, and stool. Sputum examination and Gram stain are unlikely to diagnose anthrax. PCR and immunohistochemistry may be helpful. Nasal swabs for spores from likely exposed individuals are not recommended because the expected value of the method is unknown.

Chest radiography (or CT) should be obtained when respiratory symptoms are present. Typically, radiography will show a widened mediastinum (due to enlarged hemorrhagic lymph nodes) and pleural effusion. Pneumonic infiltrates are uncommon. Lumbar puncture should be performed when meningeal symptoms or altered mental status are present. Enzyme-linked immunosorbent assay is available, but confirmation requires a 4-fold change in antibody titer in acute to convalescent specimens.

How is anthrax treated?

People exposed to the inhaled form require treatment with oral ciprofloxacin 500 mg (10-15 mg/kg for children) or doxycycline 100 mg (2.5 mg/kg for children) for 60 days. In cases where ciprofloxacin and doxycycline are contraindicated, amoxicillin 500 mg (25-30 mg/kg for children) is the drug of choice. Treatment for anthrax for 60 days after exposure provides optimal protection. Vaccination should be given even after exposure.

Cutaneous anthrax is treated with ciprofloxacin 500 mg orally (10-15 mg/kg for children) or doxycycline 100 mg orally (2.5 mg/kg for children) for 7-10 days. Treatment for anthrax is extended to 60 days if there was a possibility of inhalation exposure. With treatment, deaths are rare, but the lesion will progress through an eschar phase.

Inhalation anthrax and other forms of anthrax, including cutaneous anthrax with significant edema and skin symptoms, require treatment with 2 or 3 drugs: ciprofloxacin 400 mg IV (10-15 mg/kg for children) every 12 hours or doxycycline 100 mg IV (2.5 mg/kg for children) every 12 hours, along with penicillin, ampicillin, imipenem-cilastatin, meropinem, rifampin, vancomycin, clindamycin, or clarithromycin. Glucocorticoids may be useful in the treatment of anthrax, but they have not been adequately evaluated. With early recognition and intensive care, including mechanical ventilation, fluid replacement, and vasopressors, mortality can be reduced to 50%. The risk of death is high if treatment is delayed (usually due to late diagnosis).

Antibiotic resistance is a matter of theoretical debate. Although the pathogen is nominally sensitive to penicillin, beta-lactamases induced by Bacillus anthracis have been detected, so treatment with either penicillin or cephalosporin alone is not recommended. Military researchers may have created multidrug-resistant strains of anthrax, but these strains have not yet manifested themselves clinically.

How is anthrax prevented?

For people at high risk for anthrax (military personnel, veterinarians, laboratory technicians, textile workers who handle imported cattle wool), anthrax vaccine may be given. The anthrax vaccine is a mixture of wall-free culture filtrates. Booster vaccination is required to provide adequate protection. Local reactions to the vaccine may occur. The CDC recommends that vaccination be combined with prophylactic antibiotic therapy in patients exposed to the spores. Some evidence suggests that cutaneous anthrax does not result in acquired immunity, especially in patients who have previously received effective antimicrobial treatment. Inhalational anthrax may result in acquired immunity, but data are limited.

What is the prognosis for anthrax?

Anthrax has a 100% mortality rate if the inhalation and meningeal forms of the disease are not treated. In the cutaneous form of anthrax, the mortality rate fluctuates between 10-20%. In the gastrointestinal form, approximately 50%. In the oral form, 12.4-50%.