ANTHRAX (Bacillus anthracis) OVERVIEW
Naturally Occurring Anthrax
Anthrax, a gram-positive spore-forming rod, is a zoonotic disease rarely seen in the United States. In humans, anthrax has three somewhat clinically distinct syndromes: cutaneous, inhalation and gastrointestinal. The cutaneous form occurs most frequently on the hands, forearms, neck and face of persons working with infected livestock (cattle, sheep, goats and horses). Gastrointestinal anthrax is transmitted to humans by ingesting insufficiently cooked meat from infected animals. Inhalation anthrax, also known as Woolsorter's disease, results from the inhalation of spores and occurs primarily in persons who handle contaminated hides, wool, and furs. Prior to the cases reported after the events of September 11, 2001, no case of inhalation anthrax had been reported in the United States since 1978.
Bioterrorism Epidemiology
Anthrax bacteria are easy to cultivate and spore formation is readily induced. The spores are highly resistant to sunlight heat and disinfectants. As a bioterrorism agent, anthrax can be delivered as a bio-aerosol. Anthrax is not transmitted from person to person. If anthrax spores are released intentionally as a bio-aerosol, there will be a sudden influx of many persons with severe flu-like symptoms seeking treatment in the hospital's emergency rooms. Most likely, these persons will require assisted ventilation and immediate antibiotic support. The mortality rate will be high even in the setting of modern medical technology.
Incubation Period
The incubation period for inhalation anthrax is normally 1 - 6 days but may be as long as 60 days after spores are released. During an outbreak of inhalation anthrax in the Soviet Union in 1979, exposed persons became ill up to six weeks after the aerosol release.
Clinical Presentation
A. Cutaneous Anthrax
Infections of the skin, commonly exposed hands, forearms and head, occur when the spore enters a cut or abrasion on the skin. This form of anthrax is seen in persons handling wool, hides, leather and hair products from contaminated animals. Skin infection begins as a raised, pruritic bump or papule that resembles an insect bite. Within 1-2 days, the bump fills with fluid and then ruptures to form a painless ulcer (eschar) with a characteristic black necrotic area in the center. After about 1 - 2 weeks, the lesion dries and the eschar separates from the skin leaving a permanent scar. There is pronounced edema associated with the ulcer due to the release of edema toxin by B. anthracis resulting in swelling of the lymph glands in the adjacent area. Approximately 20% of the untreated cases result in death, either because the disease becomes systemic or because of respiratory distress caused by edema in the cervical or upper thoracic region.
B. Gastrointestinal Anthrax
The gastrointestinal form of the disease is generally caused by consumption of contaminated meat. There are two possible clinical presentations: abdominal and oropharyngeal.
Abdominal symptoms include nausea, loss of appetite, vomiting and fever followed by abdominal pain, vomiting of blood and possibly severe, bloody diarrhea. Lesions may be seen in the colon.
The oropharyngeal form generally presents with edema and tissue necrosis in the cervical area. The primary clinical presentation would be sore throat, dysphagia, fever, and regional lymphadenopathy in the neck and toxemia.
C.Inhalation Anthrax
Initially the disease onset is insidious with non-specific flu-like symptoms including fever, dyspnea, malaise, fatigue, headache, vomiting, chills, and abdominal discomfort. The person may also develop a non-productive cough and mild chest discomfort. These initial symptoms may be followed by a short period (several hours to 2 - 3 days) of improvement followed by an abrupt onset of severe respiratory distress with dyspnea, diaphoresis, stridor (high-pitched whistling respirations) and cyanosis. Septicemia, shock and death occur within 24-36 hours after the onset of respiratory distress and mortality approaches 100%. Approximately 50% of cases will develop hemorrhagic meningitis.
