Clinical aspects, diagnosis and treatment of anthrax

There are three clinical presentations of anthrax in humans: cutaneous (>95% of cases), orogastric and inhalational. The infectious form, the spore, enters the body and is thought to germinate within macrophages either at the site of inoculation (cutaneous or orogastric) or in the regional lymph node (inhalational). The bacillus then synthesizes its antiphagocytic capsule and the lethal and oedema toxins which interfere with the non-specific host defences leading to the characteristic locally destructive lesion and spread by lymphatics to the systemic circulation and other organs. The cutaneous form begins as a papule which progresses over several days to a vesicle and then ulcerates. There is often oedema, sometimes massive, probably due to the oedema toxin that surrounds the lesions which then develop a characteristic black eschar. The patient may be febrile with mild to severe systemic symptoms of malaise, headache and toxicity. Oropharyngeal anthrax presents with severe sore throat or an ulcer in the oropharyngeal cavity associated with neck swelling, fever, toxicity and dysphagia. Gastrointestinal anthrax begins with anorexia, nausea, vomiting and abdominal pain which may be similar to an acute abdomen. There may be diarrhoea and ascites, both of which may be haemorrhagic. Inhalational anthrax begins with non-specific symptoms of malaise, fever, myalgia and non-productive cough. After a period of 2-3 days, this is followed by a sudden onset of severe respiratory distress associated with diaphoresis, cyanosis and increased chest pain. There may be a widened mediastinum and pleural effusions on chest X-ray. Death follows in 24-36 h from respiratory failure, sepsis and shock. The diagnosis of anthrax is easy if it is considered. The organism is readily observed by Gram or Wright stain in local lesions or blood smear and can be easily cultured from the blood and other body fluids. However, because of its rarity, it is not often included in the differential diagnosis and in inhalational disease the diagnosis is rarely made until the patient is moribund. More rapid diagnostic tests are under development. Penicillin, combined with supportive care, remains the mainstay of treatment, although the organism is susceptible in vitro to many antibiotics. In recent years, there have been significant advances in our knowledge of the organism and its toxins and it is anticipated that similar progress will be made in the future in developing more rapid diagnostic tests and new modalities of treatment.