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Bacillus Anthracis: Characteristics, Symptoms & Treatment

Instructor: Thomas Higginbotham

Tom has taught math / science at secondary & post-secondary, and a K-12 school administrator. He has a B.S. in Biology and a PhD in Curriculum & Instruction.

Anthrax is caused by the bacterium Bacillus anthracis. This bacterium has several traits that make it an ideal choice for those who develop bioweapons. In this lesson, learn about those traits and much more about this bacterium.

Anthrax - The Big Scare after 9/11

On the heels of the 9/11 terrorist attacks, American nerves were frayed. Matters weren't helped when less than a week later, bioterrorism landed on American shores. Letters containing anthrax spores started arriving in the offices of various media outlets and U.S. legislative members. A total of twenty-two people were sickened, five of whom died. Additionally, several of those infected report long-term health conditions from their illness. What is it that can cause such a panic, why is it such a high bioterrorism risk, and why is it such a dangerous disease? Answering these questions requires a description of the causative agent for anthrax and the types of illness it can cause.

Bacillus anthracis - Causative Agent for Anthrax

The aerobic, gram-positive bacterium Bacillus anthracis is the causative agent for anthrax, an often fatal illness. B. anthracis is found naturally in soils throughout the world, and it has long been known as a disease that could kill large quantities of grazing livestock. An animal vaccine against anthrax was first developed by Louis Pasteur in the late 20th century. Human infection with B. anthracis is uncommon; most occurrences result from exposure to infected animals, usually either in agricultural workers in fields grazed by infected animals or workers in factories that process animal parts (e.g., tanneries). However, there are several key features of B. anthracis that make it a fearsome antigen.

Super Spores

One of the key features of B. anthracis that makes it so frightening is its nearly indestructible spores (i.e., a protected, dormant form of the bacterium). Because of a multi-layered coat, the spores can survive for years or even decades until activated into a vegetative state by favorable environmental conditions. The spores resist high heat, desiccation, and many common disinfectants, including one of the most commonly used laboratory disinfectants, 95% ethanol. With its hard to kill spores, anthrax has long been considered an ideal agent for bio weaponry, since the spores can be made into a powder and successfully disseminated easily, with the capacity to induce often-fatal illness.

Super Toxins

There are plenty of microbes that have 'nearly indestructible' spores. After all, that's exactly how spores evolved - to protect microbes when environmental conditions became unfavorable (such as in droughts or long, cold winters) by putting the bacterium into a protected resting state. However, few microbes combine the toughness of B. anthracis spores with its capacity to cause fatal disease. B. anthracis is a complex 'poison factory' with a highly effective defense against the body's natural defenses. B. anthracis produces three separate toxins, one causing edema (swelling and fluid buildup in tissues), one causing hemorrhage (massive bleeding), and another causing necrosis (tissue death). If those three aren't scary enough, it also produces a capsule that prevents the human immune system from being able to engulf it, which is normally the body's key defense against antigens.

Different Types of Anthrax

The method by which B. anthracis spores are introduced to a host determines the type of illness that results. Broadly speaking, a cutaneous (i.e., skin) infection results in cutaneous anthrax. Inhaled B. anthracis spores result in inhalation anthrax. Ingested B. anthracis spores result in gastrointestinal anthrax.

Cutaneous Anthrax - Most Common and Least Fatal

Cutaneous anthrax is by far the most common form of anthrax, constituting over 90% of known human cases of anthrax. It is also the least fatal, with survival rates for appropriately treated patients nearing 100%. Untreated, it is estimated that approximately one in five patients with cutaneous anthrax will die. Cutaneous anthrax is usually initiated when workers come into contact with infected animals, or with the soil where infected animals have been, and most commonly occurs on the hands, forearms, head and neck. Symptoms generally develop one to seven days after exposure to the B. anthracis spores, and include an initial lesion that turns black within a few days. This black lesion, called an eschar, is painless and surrounded by swelling. The eschar will generally resolve and leave minimal scarring in two to six weeks. However, if B. anthracis gets into the bloodstream and other parts of the body, septicemia (blood infected with the bacterium) can result, usually causing rapid death.

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