What is the leading cause of liver disease? What could cause so many people to require liver transplants? Most people on the street today would think that the answer to those questions would be alcoholism. And, although alcohol does do its fair share of damage to livers around the world, there is a greater source causing chronic liver disease out there.
This term paper will attempt to shed light on the hepatitis virus. The correct pronunciation would be: (h-p ? t? t-s). There are several strains of the hepatitis virus with some being non-issues and others being incurable killers. This report focuses specifically on the Hepatitis C virus which falls under the incurable killer header. This strain of the viruses can never be taken lightly.
There are many ways for an individual to acquire the hepatitis C virus into their system; however, there is currently no cure once it has been introduced into the system. When someone contracts the disease associated to the hepatitis virus, consider that 75 to 85% of those infected individuals will develop chronic liver disease and of that percentage 1 to 5% of the infected individuals may die from liver related complications. This report will attempt to present some history of the virus; its molecular structure; the replication of genome; modes of infection and finally some treatment methodologies.
Around 1989, after Scientists finally understood that the human immunodeficiency virus was the major cause of AIDS, another break through occurred. "...a second virus which causes persistent infection -- hepatitis C, or HCV was identified." (Askari and Cutler) Prior to the hepatitis C virus being identified, the majority of cases regarding liver failure were called "cryptogenic," or in laymen terms - 'we ain't got a clue.' In hindsight, scientists now know what caused the so called cryptogenic diseases of the liver. The disease must have been infecting us humans for a long time. Today, of course, doctors know that hepatitis C was and continues to be the main cause of chronic cirrhosis, liver failure and liver cancer. Similar to many human immunodeficiency virus infections, the hepatitis C viral infection has been proven to lay dormant in carriers for many years without demonstrating symptoms. "What is striking about hepatitis C, in contrast to human immunodeficiency virus, is that about 2% of the United States population was already infected with hepatitis C when the virus was first discovered. HIV is 4-fold less common in this country." (Askari and Cutler)
Scientists now know that a number of viruses can cause acute viral hepatitis in humans. There have been five strains identified to date and they have been classified as hepatitis A through E. Apparently there are more strains yet to be discovered by the scientific community has at least ten other viruses currently under the radar. Hepatitis C causes an inflammation of the liver and is currently incurable. An individual can get the viral infection from various sources "including: viruses, toxic chemicals, alcohol consumption, parasites and bacteria, and certain drugs. Symptoms of hepatitis are nausea, fever, weakness, loss of appetite, sudden distaste for tobacco smoking, and jaundice."(The Columbia Encyclopedia) But, when we consider Hepatitis C, we must first understand the A and B. strains so as to aid in the explanation of how we got to where we are today with some semblance of order.
Hepatitis A, often called infectious hepatitis, has been known to occur during epidemics because the virus is prevalent in human feces. The A strain is easily transmitted through food that was prepared by an individual already infected with the virus who has not washed their hands. Those signs that we hopefully see in a restaurant's restroom that state 'All Employees Must Wash Their Hands' can be attributed to this type of virus. Of course active infections are also easily spread through physical contact but the disease usually is one that usually resolves itself. As of 1995, a vaccine made gamma globulin is available but is instituted only in very serious cases because one would need to get an injection by a physician.
Hepatitis B, often called serum hepatitis, is more difficult to get than the A strain because it is usually a passed through needles. Until the mid-1970's, Hepatitis B was known to be commonly transmitted to patients during blood transfusions. Today there are specific blood and plasma screening techniques that can identify the strain and therefore prevent these types of infections. Although effective, these screening tests can not totally eliminate the B. strain.
The problem is that intravenous drug users continue to spread the disease because they are in the habit of sharing contaminated needles. Other ways to get the B. strain include partner to partner sexual transmission and also from mother to baby during birth. "Some infected individuals, particularly children, become chronic carriers of the virus. Hepatitis B can progress to chronic liver disease and is associated with an increased risk of developing liver cancer." (The Columbia Encyclopedia) A vaccine, available since 1981, is recommended for all infants and others at risk for the virus. Alpha-interferon was approved as a treatment in 1992.
Hepatitis C is newly named. The virus used to be simply called non -- A or non-B hepatitis. Like its cousins, the C. strain can be transmitted through blood transfusions and of course by sharing dirty needles. But, the problem with this particular strain is that in many cases the medical community cannot actually identify a specific source of the disease. "Many of those infected have no symptoms but become carriers, and the virus may eventually cause liver damage. Blood banks routinely screen for hepatitis C" (The Columbia Encyclopedia) Hepatitis C has been identified as the main cause of liver disease and it has also recently become the most common form of chronic liver disease. There is no cure for the disease but doctors have recently begun treating the virus infection with Alpha-interferon. Another approach is the shot gun approach where a combination of a drug named ribavirin is used in conjunction with Alpha-interferon.
Some statistics relating to the viral infection demonstrate the trends of the nation. "Number of new infections per year has declined from an average of 240,000 in the 1980s to about 25,000 in 2001. Most infections are due to illegal injection drug use. Transfusion-associated cases occurred prior to blood donor screening; now occurs in less than one per million transfused unit of blood. Estimate'd 3.9 million (1.8%) Americans have been infected with HC V, of who m 2.7 million are chronically infected." (Viral Hepatitis C)
When scientists understand the structure of enzymes for a virus such as hepatitis C, they can then design and eventually create drugs with the sole intent of disabling those enzymes. Around mid-1991, Schering-Plough made the exciting announcement that it had actually identified the molecular structure of the hepatitis C virus and the key enzymes the virus used to grow and replicate. Those enzymes announced were the key enzymes of protease, helicase and polymerase. By the end of 1991, Schering-Plough introduced the new drug Intron A which was cousins of the multiple sclerosis cure all called interferon, attacked the hepatitis C enzymes which were identified only a few short months prior. The drug as predicted blocked the hepatitis C virus' ability to grow and replicate. Intron A went on to become the first drug approved in the United States by the food and drug administration for specifically treating hepatitis C
Replication of Genome
It is much easier to distinguish the hepatitis C virus as though it was a single organism. The problem is that the virus has a range of viruses all similar enough to be called the hepatitis C virus but different enough to be classified into minor subgroups. "Viruses are microscopic and no person could ever see them with the naked eye. Indeed, HCV is so small that there's been no confirmed actual sighting of it using any type of microscope yet developed." (Hepatitis) Scientists have a better way of classifying the virus.
They classify them by their 'genotypes' and 'subtypes.' Imagine a group of cats we call 'felines ' that have evolved over time into different types of cats. These levels would be the Genotypes. The subtypes would be a Siamese cat and a black cat. Both are cats but they are not totally equal.
Most scientists believe that the hepatitis C virus evolved over a several thousand years and that is why there are unique global patterns of genotypes and subtypes:
1a - mostly found in North & South America; also common in Australia
1b - mostly found in Europe and Asia.
2a - is the most common genotype 2 in Japan and China.
2b - is the most common genotype 2 in the U.S. And Northern Europe.
2c - the most common genotype 2 in Western and Southern Europe.
3a - highly prevalent here in Australia (40% of cases) and South Asia.