Anthrax is a serious infectious disease caused by the bacterium Bacillus anthracis, found naturally in soils worldwide. While primarily affecting animals, it can also transmit to humans.
The Bacterial Core: Bacillus anthracis
Anthrax originates from the bacterium Bacillus anthracis, a rod-shaped, Gram-positive microorganism often appearing in chains. This bacterium possesses a unique ability to form highly resilient structures called spores.
These spores are dormant forms of the bacterium. They are incredibly tough, capable of surviving for decades in harsh conditions such as extreme temperatures, dehydration, and ultraviolet radiation. Spore formation occurs when the active bacteria encounter unfavorable environmental conditions, particularly when exposed to oxygen outside a living host. These resilient spores are the primary infectious agents that initiate anthrax disease.
The Potent Weapons: Anthrax Toxins
Once Bacillus anthracis spores enter a host and transform into active bacteria, they produce anthrax toxins. These toxins cause the severe symptoms of the disease. The anthrax toxin is a combination of three distinct protein components: Protective Antigen (PA), Edema Factor (EF), and Lethal Factor (LF).
Individually, these three proteins are not harmful. However, they combine in specific ways to form two potent toxins: Edema Toxin and Lethal Toxin. Edema Toxin is formed when Protective Antigen combines with Edema Factor, while Lethal Toxin results from the combination of Protective Antigen and Lethal Factor. Protective Antigen acts as a delivery mechanism, enabling Edema Factor and Lethal Factor to enter host cells and exert their damaging effects.
Edema Toxin primarily causes significant fluid accumulation, leading to swelling, by disrupting normal cellular signaling pathways through an increase in cyclic AMP (cAMP) levels. Lethal Toxin, on the other hand, functions as an enzyme that targets and cleaves essential signaling proteins within cells, particularly those involved in cell growth and immune responses. This action can lead to cell death and suppression of the host’s immune system, contributing to the rapid progression and severity of the disease.
From Spore to Sickness: How Anthrax Causes Disease
The process of anthrax causing illness begins when dormant Bacillus anthracis spores enter the body. The route of entry, such as through breaks in the skin, inhalation into the lungs, or ingestion, determines the initial site of infection and influences the type of anthrax disease that develops. For instance, inhaled spores travel to the lungs, where they are often engulfed by immune cells called macrophages.
Inside these immune cells, or sometimes in surrounding tissues, the spores encounter a favorable environment that triggers their germination. During germination, the dormant spores transform into active, multiplying vegetative bacteria. These active bacteria then multiply rapidly and begin to produce the potent anthrax toxins, Protective Antigen, Edema Factor, and Lethal Factor.
The toxins then disseminate throughout the body, causing widespread damage and the characteristic symptoms of anthrax. Edema Toxin contributes to significant swelling and fluid buildup, while Lethal Toxin disrupts critical cellular functions and can lead to the death of various cells, including immune cells. This combined action allows the bacteria to evade the immune system and proliferate, ultimately leading to severe tissue damage, organ dysfunction, and systemic illness if left untreated.