At the inhalation or contraction of the disease, those Anthrax spores enter the lungs of the host, with the finest particles entering the deepest. After entering the lungs, the spores would initially be dormant; they then grow into the bacterial form, which is bacillus anthracis.
At this stage, the immune system starts to attack the spores. Some of them are killed, but some reach the lymph nodes and some other body parts to further develop. Antibiotics would do a good job at this point. From the experiments done on the animal, it was observed that vaccines, too, would surely work at this stage, but humans have not been experimented with.
The Bacteria inside the human body would keep breeding and multiply, thus producing toxins that can cause tissue damage build-up of fluid and massive bleeding. The multiplication of these anthrax spores would only stop of all the anthrax spores are killed.