Tetanus is a unique disease. It is not transmitted from person to person, and is only acquired when the infectious agent enters the body through a wound. The organism responsible for the disease, the bacteria Clostridium tetani, cannot be eradicated because it is found in the soil, intestine, and feces of humans and farm and household animals in the form of spores which are resistant to chemicals and heat and can survive decades. The pathology of the disease is caused by a potent neurotoxin released by the bacteria, so low levels of infection can be enough to cause death, and recovering from the disease does not produce immunity (there is no natural immunity). Only vaccination confers immunity to the disease. Today in the US there are about 30 cases of tetanus per year, mostly in unvaccinated individuals or those who did not receive booster shots. The video below from the folks at the Gene Technology Access Center contains excellent animations that explain the process of infection and how the pathology of this vaccine-preventable disease is produced.