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Although you hear more about diseases like AIDS, hepatitis C is the most common blood-borne infection in the United States. It's passed on through intravenous drug use, blood transfusions and other blood products and through sexual contact. It affects more than 4 million Americans and is a leading cause of liver cancer and cirrhosis of the liver, causing more than 8,000 deaths a year.

One challenge associated with this infection is that it can be very persistent, causing chronic infections and remaining unresponsive to therapy.

Now researchers at UT Southwestern Medical Center at Dallas and The University of Texas Medical Branch at Galveston have found why the virus is so persistent. They've also found new drugs that may help fight it. The virus appears to block the immune response of infected cells, keeping the cells from being able to fight off the viral infection.

The researchers tested a class of drugs called protease inhibitors to both attack the virus and restore the cells' immune response. Protease is an enzyme needed by viruses. Blocking this enzyme keeps the virus from working. These drugs were already being tested to treat hepatitis C, but researchers were surprised to find that the drugs not only fought the virus but also kept the virus from blocking the normal immune response. Once the immune response was restored, cells cleared the virus rapidly. In the study, the virus was down to undetectable levels within days.

Researchers plan more trials of these new drugs.