Anthrax

Anthrax is an acute infectious disease caused primarily by the bacterium Bacillus anthracis, with rare cases attributed to Bacillus cereus biovar anthracis. The organism forms hardy endospores capable of surviving in soil and animal products for decades. Human infection arises through contact with these spores via the skin, respiratory tract or gastrointestinal tract. Although uncommon in modern industrialised regions, anthrax remains a public health concern in many agricultural areas of Africa and central and southern Asia, where livestock contact is frequent and environmental spores persist. The disease has also drawn global attention due to its historical and contemporary use in biowarfare and terrorism.

Historical background and etymology

Anthrax has been recognised since antiquity. The name derives from the Greek word ánthrax, meaning “coal”, referring to the characteristic black eschar found in cutaneous infections. Early English usage appeared in the fourteenth century. Throughout history the disease has been known by various names reflecting affected populations and clinical manifestations, including “woolsorters’ disease”, “charbon”, “malignant oedema”, “splenic fever” and “Siberian plague”. The first clinical descriptions of cutaneous anthrax date from the mid-eighteenth century, but scientific understanding advanced markedly in 1876 when Robert Koch identified B. anthracis as the causative agent, providing fundamental evidence for the germ theory of disease.

Transmission and risk factors

Anthrax is not usually transmitted from person to person. Instead, infection occurs through exposure to bacterial spores, which commonly contaminate the hides, wool and meat of infected herbivorous animals. Humans typically contract the disease by:

• Handling infected animals or animal products
• Inhalation of aerosolised spores
• Ingestion of contaminated meat
• Contact of spores with broken skin

Occupational groups at heightened risk include farmers, veterinarians, abattoir workers and laboratory personnel. Military personnel may be exposed in settings where anthrax spores pose a biothreat.

Clinical forms and symptoms

Anthrax presents in several distinct clinical forms, each associated with a specific route of entry and differing in severity and prognosis.

Cutaneous anthrax

Cutaneous anthrax is the most common and least lethal form, accounting for approximately 90–95 per cent of reported cases. It arises when spores enter through the skin, usually via abrasions. Symptoms begin with a small, itchy papule that progresses to a vesicle and then to a painless ulcer featuring a characteristic black eschar. Local swelling and nearby lymphadenitis often accompany the lesion. Without treatment, mortality is around 20–23 per cent, but prompt antibiotic therapy reduces fatality to under 1 per cent.

Injection anthrax

Injection anthrax, first documented in Europe in 2009 among heroin users, results from spores introduced via contaminated injected drugs. Unlike cutaneous anthrax, lesions often lack a distinct black eschar and may spread rapidly into deep muscle compartments, causing severe soft-tissue infection. Early recognition is difficult, and mortality can be significant if treatment is delayed.

Inhalation anthrax

Inhalation anthrax is the most severe form and follows inhalation of aerosolised spores. After an incubation period that may vary from a few days to more than two months, patients develop non-specific prodromal symptoms resembling influenza, including fever, chills, malaise and cough. Rapid progression follows, marked by dyspnoea, chest pain, diaphoresis and altered mental status. A hallmark of the disease is haemorrhagic mediastinitis, caused by infection of mediastinal lymph nodes, which leads to mediastinal widening and respiratory compromise. The fulminant stage is associated with septic shock and carries high mortality even with aggressive treatment.

Gastrointestinal anthrax

Gastrointestinal anthrax occurs from consumption of contaminated meat. It presents with abdominal pain, bloody or watery diarrhoea, nausea and vomiting. Lesions may form in the oropharynx or throughout the intestinal tract. Once systemic spread begins, the disease can progress rapidly, with mortality ranging from 25 to 75 per cent despite therapy.

Bacteriology and pathogenesis

Bacillus anthracis is a large, Gram-positive, rod-shaped, facultatively anaerobic bacterium. It forms resistant endospores that persist in the environment. Virulence depends on two main factors:

• A poly-D-glutamate capsule, which inhibits phagocytosis
• Anthrax toxins, comprising protective antigen, lethal factor and oedema factor

These components disrupt immune responses, promote tissue necrosis and contribute to systemic shock. After spore entry into the body, germination occurs within macrophages, followed by bacterial proliferation, toxin release and dissemination via the bloodstream.

Diagnosis

Diagnosis relies on a combination of clinical suspicion and laboratory confirmation. Investigations include:

• Microscopy and culture of blood, skin lesions or respiratory secretions
• Polymerase chain reaction testing for bacterial DNA
• Detection of anthrax toxins or specific antibodies in serum

Early recognition significantly improves outcomes, particularly in inhalation and gastrointestinal disease.

Prevention

Preventive strategies focus on reducing exposure to spores and immunisation in high-risk settings.

• Vaccination is recommended for laboratory staff, military units and other individuals at elevated risk.
• Livestock vaccination programmes are essential in endemic regions to prevent animal outbreaks and reduce human exposure.
• Post-exposure prophylaxis with antibiotics such as ciprofloxacin, levofloxacin or doxycycline, administered for up to two months, can prevent disease following known or suspected environmental exposure.

Industrial hygiene measures, including safe handling of animal products and improved abattoir practices, further reduce occupational risk.

Treatment

Management of anthrax depends on the clinical form and severity. Antibiotics remain the cornerstone of therapy. Agents commonly used include fluoroquinolones, tetracyclines and β-lactams, often in combination for systemic infections. For inhalation and disseminated anthrax, adjunctive antitoxin therapy targeting the anthrax toxin components may be employed. Supportive care in an intensive care setting is frequently required in severe cases.

Epidemiology

Anthrax is now rare in humans, with an estimated annual global incidence of around 2,000 cases. The disease is most prevalent in agricultural regions of Africa, central Asia and parts of the Middle East. Sporadic outbreaks occur in Southern Europe, while Northern Europe and North America report only isolated cases. Skin infections represent the overwhelming majority. Before the widespread adoption of vaccination and improved animal husbandry in the twentieth century, anthrax caused extensive losses among both people and livestock.

Anthrax and bioterrorism

Anthrax has a long association with biological warfare. Several nations have researched or weaponised B. anthracis, and the Biological Weapons Convention of 1975 formally prohibited such activities. Despite this, anthrax remains a bioterrorism concern. Delivery methods include aerosol dispersal and contamination of livestock or consumer goods. High-profile incidents include the 2001 anthrax letter attacks in the United States and earlier attempts by extremist groups in Japan.