M. bovis, a specific species of bacterium, causes bovine tuberculosis. Bovine tuberculosis mostly affects cattle, although it may infect virtually any mammal, causing general disease, coughing, and death. It may be passed from animals to people as well as from humans to other animals. Transmission between people is usually through the air when someone with infected lungs breathes out aerosolized bacteria. Bovine tuberculosis has been found in human lungs only after autopsy. Such cases are rare but have been reported. Person-to-person transmission has never been documented. The best protection against bovine tuberculosis is vaccination. There are two types of vaccine available: live and killed. The live vaccine protects cows by stimulating their immune systems to produce antibodies that fight off infection. It must be given together with an antibiotic so that it will be taken up by cells where it can cause no harm but instead stimulates a strong immune response. This approach does not work for humans. The killed vaccine contains parts of the M. bovis bacterium already weakened so that they do not cause problems for vaccinated animals but can still cause disease in unvaccinated ones. It should not be used in pregnant cows or cows about to give birth because it could cause premature delivery or affect the calf's health.