21.2 Bacterial infections of the skin and eyes  (Page 9/17)

The vast majority of anthrax cases (95–99%) occur when anthrax endospores enter the body through abrasions of the skin. Shadomy, S.V., Traxler, R.M., and Marston, C.K. “Infectious Diseases Related to Travel: Anthrax” 2015. Centers for Disease Control and Prevention . http://wwwnc.cdc.gov/travel/yellowbook/2016/infectious-diseases-related-to-travel/anthrax. Accessed Sept 14, 2016. This form of the disease is called cutaneous anthrax. It is characterized by the formation of a nodule on the skin; the cells within the nodule die, forming a black eschar , a mass of dead skin tissue ( [link] ). The localized infection can eventually lead to bacteremia and septicemia . If untreated, cutaneous anthrax can cause death in 20% of patients. US FDA . “Anthrax.” 2015. http://www.fda.gov/BiologicsBloodVaccines/Vaccines/ucm061751.htm. Accessed Sept 14, 2016. Once in the skin tissues, B. anthracis endospores germinate and produce a capsule, which prevents the bacteria from being phagocytized, and two binary exotoxins that cause edema and tissue damage. The first of the two exotoxins consists of a combination of protective antigen (PA) and an enzymatic lethal factor (LF), forming lethal toxin (LeTX). The second consists of protective antigen (PA) and an edema factor (EF), forming edema toxin (EdTX).

Less commonly, anthrax infections can be initiated through other portals of entry such as the digestive tract ( gastrointestinal anthrax ) or respiratory tract ( pulmonary anthrax or inhalation anthrax ). Typically, cases of noncutaneous anthrax are more difficult to treat than the cutaneous form. The mortality rate for gastrointestinal anthrax can be up to 40%, even with treatment. Inhalation anthrax, which occurs when anthrax spores are inhaled, initially causes influenza-like symptoms, but mortality rates are approximately 45% in treated individuals and 85% in those not treated. A relatively new form of the disease, injection anthrax , has been reported in Europe in intravenous drug users; it occurs when drugs are contaminated with B. anthracis . Patients with injection anthrax show signs and symptoms of severe soft tissue infection that differ clinically from cutaneous anthrax. This often delays diagnosis and treatment, and leads to a high mortality rate. Berger, T., Kassirer, M., and Aran, A.A.. “Injectional Anthrax—New Presentation of an Old Disease.” Euro Surveillance 19 (2014) 32. http://www.ncbi.nlm.nih.gov/pubmed/25139073. Accessed Sept 14, 2016.

B. anthracis colonies on blood agar have a rough texture and serrated edges that eventually form an undulating band ( [link] ). Broad spectrum antibiotics such as penicillin , erythromycin , and tetracycline are often effective treatments.

Unfortunately, B. anthracis has been used as a biological weapon and remains on the United Nations’ list of potential agents of bioterrorism . United Nations Office at Geneva. “What Are Biological and Toxin Weapons?” http://www.unog.ch/80256EE600585943/%28httpPages%29/29B727532FECBE96C12571860035A6DB?. Accessed Sept 14, 2016. Over a period of several months in 2001, a number of letters were mailed to members of the news media and the United States Congress. As a result, 11 individuals developed cutaneous anthrax and another 11 developed inhalation anthrax. Those infected included recipients of the letters, postal workers, and two other individuals. Five of those infected with pulmonary anthrax died. The anthrax spores had been carefully prepared to aerosolize, showing that the perpetrator had a high level of expertise in microbiology. Federal Bureau of Investigation. “Famous Cases and Criminals: Amerithrax or Anthrax Investigation.” https://www.fbi.gov/history/famous-cases/amerithrax-or-anthrax-investigation. Accessed Sept 14, 2016.