Clinical Presentation of Anthrax
More than 95% of cases of anthrax worldwide are cutaneous (Figure 1). After anthrax spores enter the body, the incubation period is 1 to 5 days. The disease first appears as a small papule, or growth, that progresses over a day or two to a blister containing serosanguinous fluid (clear mixed with small amounts of blood) with few white blood cells (puss or leukocytes). The blister, which may be 1 to 2 cm in diameter, ruptures, leaving a necrotic ulcer. Satellite blister may also be present. The lesion is usually painless, and varying degrees of edema (swelling) may be present around it. The edema may occasionally be massive, encompassing the entire face or limb, and is described by the term “malignant edema.” Patients usually have fever, malaise (fatigue), and headache, which may be severe in those with extensive edema. There may also be local swelling and tenderness of the lymphnodes (lymphadenitis). The ulcer base develops a characteristic black scab (eschar) and after a period of 2 to 3 weeks the scab separates, often leaving a scar. Shock due to bacteria in the blood (septicemia) is very rare, and with treatment mortality should be less than 1%.
Inhalational anthrax begins after an incubation period of 1 to 6 days with nonspecific symptoms of fatigue, muscle pains (myalgia), and fever. There may be an associated nonproductive cough and mild chest discomfort. These symptoms usually persist for 2 or 3 days, and in some cases there may be a short period of improvement. This is followed by the sudden onset of increasing respiratory distress with shortness of breath (dyspnea), difficulty breathing (stridor), insufficient oxygenation (cyanosis), increased chest pain, and sweating (diaphoresis). There may be associated edema (swelling) of the chest and neck.
Chest X-ray examination usually shows the characteristic widening of the mediastinum and, often, pleural effusions (fluid collecting around the lung) (Figure 2). Pneumonia has not been a consistent finding but can occur in some patients1. While cases of inhalational anthrax have been rare in this century, several have occurred in patients with underlying pulmonary disease, suggesting that this condition may increase susceptibility to the disease2. Meningitis is present in up to 50% of cases, and some patients may present with seizures. The onset of respiratory distress is followed by the rapid onset of shock and death within 24 to 36 hours. Mortality has been essentially 100% despite appropriate treatment.
Fig. 2. This x-ray, taken on day 2 of illness, shows the lungs of a 51-year-old laborer with occupational exposure to airborne anthrax spores. Marked mediastinal widening is evident, with a small parenchymal infiltrate. Reprinted from Binford CH, Connor DH, eds. Pathology of Tropical and Extraordinary Diseases. Vol 1. Washington, DC: Armed Forces Institute of Pathology; 1976: 119. AFIP Negative 71-1290-2.
Oropharyngeal and Gastrointestinal Anthrax
Oropharyngeal and gastrointestinal anthrax result from the ingestion of infected meat that has not been sufficiently cooked. After an incubation period of 2 to 5 days, patients with oropharyngeal disease present with severe sore throat or a local oral or tonsillar ulcer, usually associated with fever, toxicity, and swelling of the neck due to cervical or swelling of the lymphnodes in the neck area (submandibular lymphadenitis) and edema. Difficulty swallowing (dysphagia) and respiratory distress may also be present. Gastrointestinal anthrax begins with nonspecific symptoms of nausea, vomiting, and fever; these are followed in most cases by severe abdominal pain. The presenting sign may be an acute abdomen, which may be associated with vomiting blood (hematemesis), fluid in the abdominal cavity (massive ascites), and diarrhea. Mortality in both forms may be as high as 50%, especially in the gastrointestinal form.
Meningitis may occur following bacteremia (bacteria in the blood), as a complication of any of the other clinical forms of the disease. Meningitis may also occur, very rarely, without a clinically apparent primary focus. It is very often hemorrhagic, which is important diagnostically, and almost invariably fatal (Figure 3).
Fig. 3. Meningitis with subarachnoid hemorrhage in a man from Thailand who died 5 days after eating undercooked carabao (water buffalo). Reprinted from Binford CH, Connor DH, eds. Pathology of Tropical and Extraordinary Diseases. Vol 1. Washington, DC: Armed Forces Institute of Pathology; 1976: 121. AFIP Negative 75-12374-3.
1. Abramova FA, Grinberg LM, Yampolskaya OV, Walker DH. Pathology of inhalational anthrax in 42 cases from the Sverdlovsk outbreak of 1979. Proc Natl Acad Sci U S A. 1993;90:2291–2294.
2. Brachman PS. Inhalation anthrax. Ann N Y Acad Sci. 1980;353:83–93.
(The above material has been derived from the U.S. Navy's Virtual Naval Hospital web site www.vnh.org)