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Over time, chronic hepatitis B virus and hepatitis C virus infections can progress to advanced liver disease, liver failure, and hepatocellular carcinoma. Unlike other forms, more than 80% of hepatitis C infections become chronic and lead to liver disease. When combined with hepatitis B, hepatitis C now accounts for 75% percent of all cases of liver disease around the world. Liver failure caused by hepatitis C is now leading cause of liver transplants in the United States.
The average human gut is home to perhaps 500 to 1,000 different species of bacteria.
Most childhood vaccines are 90–99% effective in preventing disease. Side effects are rarely serious.
Multiple sclerosis is a condition wherein the body's nervous system is weakened by an autoimmune reaction that attacks the myelin sheaths of neurons.
Cancer has been around as long as humankind, but only in the second half of the twentieth century did the number of cancer cases explode.