Anthrax

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The following is from the Merck Manual of Diagnosis & Therapy

ANTHRAX

A highly infectious disease of animals, especially ruminants, transmitted to humans by contact with the animals or their products.

Etiology and Epidemiology

The causative organism, Bacillus anthracis, is a large, gram-positive, facultatively anaerobic, encapsulated rod. The spores resist destruction and remain viable in soil and animal products for decades. Human infection is usually through the skin but has occurred after ingestion of contaminated meat. Inhaling spores under adverse conditions (eg, the presence of an acute respiratory infection) may result in pulmonary anthrax (woolsorter's disease), which is often fatal. Pulmonary anthrax follows rapid multiplication of spores in the mediastinal lymph nodes. Rarely, GI anthrax may follow ingestion of contaminated meat when a break is present in the pharyngeal or intestinal mucosa, which facilitates invasion of the intestinal wall.

Although anthrax is an important animal disease, it is rare in humans and mainly occurs in countries that do not prevent industrial or agricultural exposure to infected goats, cattle, sheep, and horses or their products. Anthrax also occurs in exotic wildlife such as hippos, elephants, and cape buffalo.

Symptoms and Signs

The incubation period varies from 12 h to 5 days (generally, 3 to 5 days).

The cutaneous form begins as a painless, pruritic, red-brown papule; as it enlarges, it is surrounded by a zone of brawny erythema and gelatin-like edema. Considerable peripheral erythema, vesiculation, and induration are present. Central ulceration follows, with serosanguineous exudation and formation of a black eschar. Local lymphadenopathy may occur, occasionally with malaise, myalgia, headache, fever, nausea, and vomiting.

Initial symptoms of pulmonary anthrax are insidious and resemble influenza. Fever increases, and within a few days, severe respiratory distress develops, followed by cyanosis, shock, and coma. Severe hemorrhagic necrotizing lymphadenitis develops and spreads to the adjacent mediastinal structures. Serosanguineous transudation, pulmonary edema, and pleural effusion occur. Hemorrhagic meningoencephalitis and/or GI anthrax may develop. Lung x-ray may show diffuse patchy infiltration; the mediastinum is widened because of enlarged hemorrhagic lymph nodes.

In GI anthrax, the released toxin induces a hemorrhagic necrosis extending to the draining mesenteric lymph nodes. Septicemia with potentially lethal toxicity ensues.

Diagnosis

The occupational and exposure history is important. Cultures or Gram stains from cutaneous lesions may be used to isolate B. anthracis, and throat swabs and sputum may be used in the pulmonary form. When primary cultures do not grow, the organism may be isolated by mouse inoculation.

Diagnosis of GI anthrax depends on recognition of clinical symptoms. Occasionally, organisms can be seen by Gram stain of vomitus or feces. Clinically, GI anthrax presents with nausea, vomiting, anorexia, and fever progressing to bowel necrosis with concurrent septicemia and death. An oropharyngeal form of anthrax presents as a mucocutaneous lesion in the oral cavity with sore throat, fever, adenopathy, and dysphagia. This proceeds to necrosis and death.

Prevention and Treatment

An anthrax vaccine, composed of a culture filtrate, is available for those at high risk (veterinarians, laboratory technicians, employees of textile mills processing imported goat hair). Repeated vaccination may be required to ensure protection. Local reactions can occur. A live toxigenic, unencapsulated avirulent animal vaccine is available for veterinary use.

Treatment of the cutaneous form with procaine penicillin G 600,000 U IM bid for 7 days prevents systemic spread and induces gradual resolution of the pustule. Progression of the lesion through the eschar phase occurs despite antibiotic therapy. Tetracycline 2 g/day in 4 divided doses po (for children, 25 mg/kg/day in 4 divided doses) is also effective. Alternatively, erythromycin, ciprofloxacin, or chloramphenicol may be used. Penicillin or erythromycin is preferred in young children. Most strains are resistant to cefuroxime.

Pulmonary anthrax is almost always fatal, but early and continuous IV therapy with penicillin G 20 million U/day may be lifesaving. (Usual dose of penicillin G is 100,000 to 250,000 U/kg/day in 4 to 6 divided doses.) It is used in combination with streptomycin 500 mg/day q 8 h IM in adults and 25 mg/kg/day in children. Corticosteroids may be useful but have not been adequately evaluated. If treatment is delayed (usually because the diagnosis is missed), death is likely.

There is no specific therapy for GI anthrax. Contaminated meat should be avoided. If ingestion occurs, prophylaxis may be given with penicillin G 4 million U q 4 h IV for 10 days.

Anthrax, contagious disease of warm-blooded animals, including humans, caused by the bacterium Bacillus anthracis. One of the oldest known diseases, it was once epidemic and still appears in many world areas, but only sporadically in the western and southern United States. It was the first disease for which the causative organism was isolated, by C. J. Davaine in 1863, for which a pure culture was obtained, by Robert Koch in 1876, and for which an effective vaccine was developed, by Louis Pasteur in 1881.
Animals acquire the disease from drinking water draining from contaminated soil, in which the organism may live for years; from eating infected carcasses and feedstuffs; and from the bites of bloodsucking insects. The disease, sometimes manifested by staggering, bloody discharge, convulsions, and suffocation, may be fatal almost immediately in acute cases and within three to five days in subacute cases. Death is caused by toxemia. Preseasonal inoculations and antibiotics are effective.
In humans, the disease appears in both external and internal forms, with a death rate of about 20 percent. The external or cutaneous form is contracted through cuts or abrasions in the skin by those who handle infected hides and carcasses and may be self-limiting, but often disseminates into the bloodstream, with fever and prostration. It is characterized by malignant pustules on exposed skin areas. The internal type is acquired by inhaling anthrax spores, as from animal hair and wool, which invade the lungs and sometimes the intestinal tract to cause hemorrhage. It is speculated that an intestinal variety may be caused by consuming contaminated meat or milk. Workers exposed to animal products, especially wool, are protected by vaccination. Penicillin and tetracyclines are effective in treatment except in rapidly progressing cases.