Cattle, sheep, and horses are the chief domestic animal hosts, but other animals may be infected.
All human populations are susceptible.
Recovery from a mild exposure to the disease may confer immunity. The spores are very stable and may remain viable for many years in soil and water. However, even anthrax spores will break down by exposure to bright sunlight. Shock and death can occur within 24 to 36 hours of severe symptoms. The Michigan Department of Public Health produced the only licensed human vaccine against anthrax.