6. Tetanus What it is: A bacterial disease that causes lockjaw, breathing problems, muscle spasms, paralysis, and death. How you get it: The bacteria that causes tetanus is found in soil, dust, and manure. It can get in your body through a cut or open sore. Why it’s serious: 10% to 20% of tetanus cases are fatal. Deaths are more common in people who are older than 60 or who have diabetes.