Labeled illustration depicting anthrax bacteria and endospores (small yellow spheres) in the blood stream (upper right) and lymphatic system. The bacteria Bacillus anthracis produces highly toxic endospores (spores) which can exist in the environment for years or even centuries. The spores may become airbourne and inhaled by mammals, including humans. The spores become active and travel through the airways to the alveoli in the lungs where they are attacked by lymphocytes. Once inside the lymphocytes some are killed but many continue to reproduce eventually killing the lymphocyte. They go on to infect the nodes of the lymphatic system (lower center) and the rest of the body, including the brain. If left untreated the infection can become fatal.