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The most destructive flu epidemic of all times in recorded history occurred in 1918, with approximately 20 million deaths worldwide.
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.
In most cases, kidneys can recover from almost complete loss of function, such as in acute kidney (renal) failure.
Multiple experimental evidences have confirmed that at the molecular level, cancer is caused by lesions in cellular DNA.
As the western states of America were settled, pioneers often had to drink rancid water from ponds and other sources. This often resulted in chronic diarrhea, causing many cases of dehydration and death that could have been avoided if clean water had been available.