What is the Medical Definition of the Disease Anthrax?
Basic Facts
Anthrax is a disease caused by the bacterium Bacillus anthracis. This microorganism is classified as a gram positive, aerobic rod. B. anthracis forms spores, which are naturally found in many soil environments. These spores, ranging in size from 2-6 microns in diameter, can survive for decades in the environment, as they are very resistant to degradation. They are also easily aerosolized. This infection is primarily a disease of herbivores, particularly cattle, due to their exposure to contaminated soil. What is the medical definition of the disease anthrax? Humans can be infected with B. anthracis, leading to three different types of disease: cutaneous, gastrointestinal, and inhalational. Each of these types of infections has different epidemiology, symptoms, prognosis, and treatment.
Cutaneous Infection
When B. anthracis spores enter a cut or wound, a cutaneous infection can occur, usually within two weeks of exposure. The initial sign of infection is a raised, red lesion (called a papule), which progresses into an ulcerated, necrotic black lesion called an eschar. Pain is generally not associated with the formation of the eschar. Other symptoms include fever, headache, nausea, vomiting, and swollen lymph nodes. Although most cases are self-limited, the infection can spread to the blood stream, leading to sepsis. Without treatment, 20% of cases are lethal. With proper antibiotic treatment, mortality decreases to 1%. Ciprofloxacin is considered first-line antibiotic therapy, though there are several other antibiotic choices to which most B. anthracis strains are susceptible.
Gastrointestinal Infections
GI infection with B. anthracis is very rare, and has never been reported in the United States. It occurs from ingestion of meat contaminated with spores. 2-5 days later, symptoms appear, including fever, abdominal pain, vomiting, diarrhea, constipation, and possibly blood in the vomit or stool. The infection causes ulcers in the GI tract and can also cause bowel perforation. If infection and ulceration occur higher, up in the oral cavity or pharynx, symptoms include swollen lymph nodes, fluid accumulation (edema), difficulty swallowing, and obstruction of the upper respiratory tract. This infection route is 25-60% fatal, and it is unknown whether early treatment is effective in decreasing mortality.
Inhalational Infection
When B. anthracis spores are inhaled, the resulting disease is invariably severe. Symptoms appear, on average, ten days after exposure, and include flu-like symptoms: fever, malaise, cough, congestion, headache, and difficulty breathing. As the disease progresses (due to lymphatic and blood spread), the infection becomes fulminant and the patient may experience abdominal or chest complaints, and eventually go into septic shock. At this later stage of disease, a chest x-ray may reveal widening of the mediastinum or pleural effusions. Mortality is estimated at approximately 75%, regardless of treatment. The inhalational form of infection is not transmitted person-to-person.
Bioterrorism
This infection is considered to be high risk for use in an attack as a bioweapon. While infection does not spread from person-to-person, the spores are highly infectious, easily aerosolized, and highly lethal. In September of 2001, B. anthracis spores were sent by U.S. mail, resulting in 22 cases of the illness: 11 inhalational and 11 cutaneous. All of the patients with cutaneous infection survived, while 5/11 inhalational cases were fatal. Due to the risk of these bacterial spores being used as a bioterror weapon, a vaccine has been developed to protect against infection. It is given to people at high risk of exposure, and there are stockpiles reserved for military personnel. Successful vaccination requires multiple doses over an 18 month period, followed by annual booster shots.
References
“Anthrax” Centers for Disease Control. https://www.bt.cdc.gov/agent/anthrax/
Lane H. C, Fauci Anthony S, “Chapter 214. Microbial Bioterrorism” (Chapter). Fauci AS, Braunwald E, Kasper DL, Hauser SL, Longo DL, Jameson JL, Loscalzo J: Harrison’s Principles of Internal Medicine, 17e
Schwartz Brian S, Chambers Henry F, “Chapter 33. Bacterial & Chlamydial Infections” (Chapter). McPhee SJ, Papadakis MA, Tierney LM, Jr.: CURRENT Medical Diagnosis & Treatment 2010