Bioterrorism: Anthrax

Anthrax is a disease caused by gram positive, rod shaped bacteria known as Bacillus Anthracis. This is a strategic weapon for bioterrorism because it is classified as a Category A organism, which means that it can spread rapidly through the air or through water. Bacillus Anthracis is gram positive, meaning it has a very thick cell wall made of a protein called peptidoglycan. It is naturally found in soil and can affect humans and animals, but is not contagious.

It has binary A-B toxins, which means that it can both transport and insert the effector toxins into the target cell, without the assistance of another organism or vector. The “A” stands for the Edema Factor and Lethal Factor, which are the toxins that invade the cell. The Edema factor is primarily responsible for throwing off water homeostasis in cells by increasing fluid retention, which in turn throws off signal transduction (aka communication between cells). The Lethal Factor helps the bacteria evade the immune system by killing macrophages. Together, these toxins aid the bacteria in proliferating and killing cells. The “B” part of the exotoxin is the Protective Antigen, which basically forms a channel through the cell surface and allows the passage of the two "A" factors into target cells .

Bacillus anthracis has a single chromosome which is a circular, 5 million base pair DNA molecule. It also has two circular, extrachromosomal, double-stranded DNA plasmids, pXO1 and pXO2. A plasmid is a genetic structure in bacterial cells that can replicate independently of chromosomes to be passed onto daughter cells. These plasmids help the bacteria survive by carrying genes responsible for getting rid of external pathogens, as well as by passing on antibiotic resistant genes. Both the pXO1 and pXO2 plasmids are required for full virulence and infectious effectiveness of the anthrax bacteria because they also code for the toxins.

Gram staining of Bacillus Anthracis.

Bacillus anthracis requires sugars, amino acids, and free oxygen in order to survive, but it is incredibly durable due to spore formation - it can lie dormant for years before entering a living host to reactivate and multiply. A spore is a cluster of bacteria in a small, spherical shape that is resistant to environmental stress and difficult to destroy. They are relatively large, from 1.0-1.2 micrometers in width and 3-5 micrometers in length.

Spores are produced when the bacteria are not vegetative cells, meaning they do not currently have the nutrients needed to grow and reproduce. The reproductive cycle begins with spore germination, when the bacteria is able to access water and nutrients. Spore germination is basically when the bacterial spores transform back into active cells. After spore germination, the bacteria are able to asexually reproduce.

A person can become infected with anthrax through ingestion of contaminated meat or water, through an open wound (which is commonly known as cutaneous transmission), or through inhalation of anthrax spores which is the most deadly method. Animals such as cows can become infected with anthrax by ingesting spores from contaminated soil, water, or food. Furthermore, people who work with animals, such as veterinarians, livestock producers, and travelers are most at risk of receiving anthrax through animal transmission, although this mode of transmission is less common.

Bacillus Anthracis damaging the epithelial barrier upon infection.

The bacteria form spores that remain dormant in harsh conditions, that then become active when they are inhaled, ingested, or come into contact with a skin lesion. Anthrax can kill anyone who inhaled the spores if they do not receive antibiotics within 24 hours. As for cutaneous Anthrax, 80% of people who are infected will die, if left untreated. Therefore, it is crucial to give out antibiotics like penicillin, ciprofloxacin, and doxycycline, to everyone in the area of exposed anthrax.

Anthrax itself is not very dangerous, the deadly toxins it secretes is. Someone can be treated with antibiotics, and the bacteria itself can disappear, but the deadly toxins can still roam in your body and kill your cells. They mainly affect your endothelial cells which line blood and lymph cells, which makes it so lethal. The toxins damage cells and much of its action takes place in the heart muscle and liver cells. For people who inhale the spores, their lungs and respiratory system will be affected. If the spores are ingested or consumed, then their stomach and digestive system will be affected.

Anthrax spores that are taken into the stomach when a person ingests contaminated food or water cause vomiting, diarrhea, and severe pain due to the inflammation of the intestines. The bacteria make holes through the intestine wall and gain access to the bloodstream. If spores in the air are inhaled, the person will develop flu-like symptoms such as a sore throat and headaches. Lymph nodes in the chest will swell, causing tightness in the chest and difficulty breathing, which can lead to shock. With cutaneous transmission, the infected person will suffer from muscle aches and swollen lymph nodes within that region.