MEDFORD — A disease that afflicts as many as 4 million Americans is the most common cause of chronic liver disease, but it produces no symptoms in about 80 percent of its victims.

MEDFORD — A disease that afflicts as many as 4 million Americans is the most common cause of chronic liver disease, but it produces no symptoms in about 80 percent of its victims.

People who have liver failure associated with hepatitis C account for about half of the liver transplants performed every year in the United States, Dr. Aijaz Ahmed said during a presentation Tuesday at the Smullin Center at Rogue Valley Medical Center. The disease also kills 8,000 to 10,000 Americans annually.

The virus remains a challenge to physicians because there's no vaccine to prevent it, and it may not be diagnosed until it has caused liver damage. It progresses at different rates, and about 15 percent of people who are infected somehow manage to clear the virus from their body without treatment. The other 85 percent eventually develop chronic infection, and 20 percent of those will suffer from cirrhosis (severe scarring) of the liver.

"Some people get liver failure," Ahmed said. "Others don't."

Ahmed, an assistant professor of medicine at Stanford Medical School, spoke to a group of about 50 people who ranged in age from their 20s to their 70s, including some who have lived with the hepatitis C virus for more than half a century. He counseled people to take an active role in managing their disease to minimize stress on their weakened liver.

"Patients have to get their act together," he said. "Lose weight, no smoking and no drinking."

Ahmed came to Southern Oregon at the invitation of Dr. Martin Tice. He presented a continuing medical education program on hepatitis C as well as his public program.

Hepatitis C spreads when blood from an infected person enters the body of someone who isn't infected. Hundreds of thousands of people were infected in the 1970s and '80s before blood products were screened for the virus. It also spreads among intravenous drug users and people who engage in high-risk sexual contact.

Six types of the virus, and many subtypes, have been detected around the world. Genotypes 1, 2 and 3 are found worldwide; genotype 4 is found mostly in Africa and the Middle East; genotype 5 exists mostly in South Africa; and genotype 6 occurs mostly in Hong Kong and Vietnam.

In the United States, genotype 1 accounts for about 70 percent of all infections. Unfortunately, Ahmed said, genotype 1 is one of the more difficult types to treat. If the national infection rate (about 1 percent of the U.S. population) were extended to Southern Oregon, that would mean as many as 2,000 people in the Rogue Valley may have hepatitis C.

Ahmed said the most common symptom of infection is severe fatigue. Some people may produce dark urine, or suffer abdominal pain, loss of appetite or nausea. Very few have the jaundiced skin associated with hepatitis.

Physicians generally treat the virus with an extended multiweek course of antiviral drugs that eliminate it in some people, but not others. The medicines produce flu-like symptoms (nausea, diarrhea, aches and pains) among many patients, as well as depression or vision disorders, so the treatment is not undertaken lightly.

Many people still have little knowledge of the virus despite its prevalence. While it is spread by contact with infected blood, it's not typically spread by ordinary sexual contact or casual physical contact. In rare cases an infected mother can pass the virus to her newborn child.

Ahmed said people who are infected should never share their razor or toothbrush with anyone else.

"Every time we brush our teeth we bleed," he said. "We just don't see it."

Cuts or scrapes should be covered to prevent exposure to others, and any bloody bandages should be disposed of.

Ahmed said people with hepatitis C can be organ donors, but they can give their organs only to other people who are already infected with the virus. If the organ donor and the recipient had different types of the virus, one type usually takes over.

Reach reporter Bill Kettler at 776-4492 or e-mail