How Do the Hepatitis B and C Viruses Work?

How do the hepatitis B and C viruses work?

How are viruses different from bacteria?

What is the difference between an acute and a chronic illness?

BY ANDREW F. BRANCA

Hepatitis is a disease of the liver that is caused by one of the tiniest types of “bugs”, or microorganisms, that can infect humans: a virus. The most common symptom of hepatitis is tiredness, or fatigue. there are several different types of hepatitis, each caused by a different hepatitis virus. In each case, the virus, once inside the body, begins to live in the liver cells and then takes them over.

What is a virus?

A virus is much simpler and much smaller than a human cell. It is, in fact, just made up of a compact string of genes (genes carry the coded information telling our cells what to do) in a coat of protein. Viruses carry only the tools they need to take over a cell. Among these basic tools for survival, the virus carries a blueprint so that it can make many more copies of itself once it has infected the cell. the protein coat around the virus – its capsule – also plays a critical role, as we will see.

Unlike a human cell, which contains complex biological machines to digest food, produce energy, and perform other functions, a virus exists mainly to reproduce. The virus reproduces by invading living cells. Once inside a cell it takes over the cell’s normal functions and uses the cell and its machinery just to produce more virus.

Not all viruses can enter all cells. The hepatitis viruses, for example, mainly infect liver cells. When a hepatitis virus bumps up against a cell that is a suitable target – usually a liver cell – the outer capsule sticks to the cell surface, and the viral genes are able to pass from the capsule into the cell.

Because the virus takes the cell’s energy away from producing the substances it needs to survive and uses it to make more virus instead, the cell’s life span is much shorter than average. Before it dies, however, the infected cell may have produced thousands of viruses, each of which will leave the dying cell and go on to infect another, healthy cell, repeating the cycle. The entire process, from the moment the virus attaches to the cell to the moment that the cell dies, releasing new virus, can be completed in a matter of hours. But because you have so many cells in your body, the process has to happen many times before you feel any symptoms.

The entire process, from the moment the virus attaches to the cell to the moment that the cell dies, releasing new viruses, can be completed in a matter of hours.

How are viruses different from bacteria?

Viruses are often confused with bacteria, the other tiny organisms that cause many common human illnesses, such as ear infections, sore throats, and infected cuts. Although both can infect people and cause disease, viruses and bacteria are very different. Bacteria, like human cells, are always active, absorbing nutrients, repairing damage, and preparing to grow and divide, among other normal activities.

Viruses, in contrast, are usually doing nothing at all unless they are actually causing infection. Viruses are also much smaller than bacteria Рso small that many of them actually infect bacteria, much as bacteria infect people. To give you an idea of how small viruses are, imagine that a virus is the size of a basketball; on that scale, the common bacteria Escherichia coli would be nearly as big as a basketball court, while a typical human cell would be as large as a football field!

Many bacterial infections are treated with common drugs called antibiotics, and once treated effectively, they are gone forever (unless you are infected again). You may have wondered why the hepatitis virus can’t be treated in the same way. Because a virus lives in the cell and uses it to reproduce more virus, most drugs that will kill the virus will harm the cell, too.

An example of a viral treatment is the drug interferon, which is used to fight hepatitis. While it has been tough to find treatments for viruses, we do have vaccines, or preventive drugs, that protect against infection by some viral diseases, such as hepatitis B, the flu, and polio.

What is the difference between an acute and a chronic illness?

Your doctor has probably told you that your hepatitis is either acute or chronic. an acute illness is one that develops quickly, has severe symptoms, and lasts for 6 months or less. A chronic illness is one that lasts longer than 6 months, and has symptoms that may disappear for a while, then recur. While some forms of hepatitis are acute, others are chronic.

Different kinds of hepatitis viruses

When hepatitis infection occurs, the liver is affected. Hepatitis simply means inflammation, or irritation, and enlargement of the liver. There are many viruses that can affect the liver, like hepatitis A, B, C, D, E, and G. Each of these diseases is caused by a different virus. Some of these do not cause serious infections, and may not even cause symptoms. (See Chapter 7.) Hepatitis A, B, and C are most likely to cause symptoms, and chronic hepatitis B and C have the greatest chance of causing long-term health problems. (There are vaccines available for hepatitis B and hepatitis A, a much less serious infection of the liver.)

Hepatitis viruses, like all viruses, are tiny invaders that enter cells, interfere with the cells’ normal activities, and force the cells to make more virus. As the hepatitis viruses work, they can kill many hepatocytes. Researchers think that besides the hepatitis viruses’ effects on liver cells, they also spur an immune attack that mistakenly targets liver cells, rather than the virus. It’s believed that the scarring caused by this immune system attach on the patient’s own body causes much of the liver damage in patients with these diseases.

The biggest differences between the hepatitis B and C viruses are in some of the ways they are spread (see Chapter 4), whether they become chronic, and in the way the hepatitis C virus mutates, or changes. A¬†mutation¬†is a permanent change in the virus’s genetic code, or makeup. Both the hepatitis B and C viruses mutate in the body, but the hepatitis C virus does this so many times that the body ends up fighting many slightly different forms (called strains) of the virus. This is why the body is so much better at fighting hepatitis B than fighting hepatitis C, and one reason why there is a vaccine for hepatitis B, but not for C. (See¬†Chapter 12.)

Hepatitis viruses, like all viruses, are tiny invaders that enter cells, interfere with the cells’ normal activities, and force the cells to make more virus.

Hepatitis B

Hepatitis B is caused by the hepatitis B virus. This virus has a ball-shaped capsule containing the virus’s genetic material, which invades the liver, as explained above. Hepatitis B is a serious form of hepatitis that affects more than 1 million Americans, with about 140,000 more becoming infected each year.

Hepatitis B virus causes the liver to become enlarged, irritated, and sometimes scarred. Hepatitis B has the ability to hide inside the body, so many people don’t know that they’ve been infected until they are tested specifically for hepatitis B. However, some infected people will have the flu-like symptoms that you would normally expect when you have a virus: loss of appetite, upset stomach and vomiting, fever, pain in the abdomen, and so on. this is called acute hepatitis. (Remember, an acute illness is short-lasting, while a chronic disease may last a long time, recurring often.)

Other symptoms of acute hepatitis B infection are very different from having the flu. For instance, your urine may become dark, which is a sign that your liver is functioning poorly. Your liver will not be as efficient in breaking down bilirubin, and so your eyes and skin may become yellowish, or jaundiced. You may feel very tired for weeks or months. This is another sign that your liver is not removing waste from your body as quickly as it should. Finally, an enlarged liver may cause a strange feeling in the right side of the abdomen that is described by many as a heavy and dragging sensation. Many people with hepatitis B have some symptoms; it is important to know, however, that some people will have no noticeable symptoms at all. (See Chapter 7 for a discussion of symptoms and how to deal with them.)

Most adults can fight off a hepatitis B infection without treatment. But a small percentage of people go on to become carriers (having few or no symptoms but able to infect other people) and a few more become chronically infected; that is, their infection stays active for more than 6 months. About 5% of adult cases and about 90% of cases in newborn babies become chronic. (See¬†Chapter 4¬†for information on how babies can be protected from hepatitis.) As the virus continually invades new cells and spurs the immune system’s reaction, more hepatocytes are damaged. The damage leads to scarring, and the constant presence of virus in the liver may lead to cirrhosis, and possibly liver cancer, particularly in patients who are untreated or have the disease for a long time. (See Chapter 2.)

Hepatitis C

Hepatitis C is caused by the hepatitis C virus, which is also a ball-shaped capsule containing the viral genes that invade the liver. Hepatitis C is a serious form of liver disease, affecting about 4 million Americans, with more than 150,000 or so becoming infected each year. Hepatitis C virus is similar to hepatitis B virus in that you can catch the disease and not feel symptoms. If you have symptoms, they may be similar to those described for hepatitis B in the previous section. The most common symptom of hepatitis C, however, is fatigue. If chronic hepatitis C is left untreated, it also can cause scarring of the liver (cirrhosis) as well as an increased chance of liver cancer, and even liver failure. Chronic hepatitis C is the leading cause of liver transplant in the United States. (See Chapter 6.)

Like hepatitis B, when the hepatitis C virus enters your liver, it begins to invade cells and grow. As it does so, increasing numbers of the cells are scarred and damaged. You may not feel any ill effects until so much damage has taken place that your liver no longer functions properly. This can take 10 to 40 years, depending on the speed at which the disease progresses and how well you take care of your liver. Alcohol use, HIV, and other factors can affect how fast the disease progresses but still, there is no way of knowing how each person’s disease will progress.

About 85% of patients with hepatitis C virus infection go on to suffer from chronic hepatitis. In the meantime, just like patients with hepatitis B, you should avoid alcohol because of the additional damage it can do to your liver (and remember, alcohol and acetaminophen [an ingredient in some over-the-counter pain relievers, and many drug combinations used for colds] taken together can cause a condition called fulminant hepatitis, which can lead to fatal liver failure. Clearly, you should never combine these two substances, and talk to your doctor about any medications you take).

All of this information about the hepatitis viruses can help you better understand how hepatitis is spread, which is the topic we will discuss in Chapter 4.

QUIZ

Q. What causes hepatitis?

A. Hepatitis is caused by a virus – one of the smallest types of “bugs” or microorganisms that can cause disease in people.

Q. Can viruses be treated with antibiotics?

A. No Antibiotics kill bacteria not viruses. Other drugs are needed to treat viruses.

Q. What is the difference between an acute infection and a chronic infection?

A. An acute infection is a sudden, extreme infection that lasts a short time, then goes away. A chronic infection lasts more than 6 months, and may recur many times, often without symptoms.

Q. What do viruses do when they infect cells?

A. They take over the cell and make it manufacture copies of the virus instead of letting it do the jobs it normally does.

ACTION STEPS

‚ÄĘ Make sure you understand what type of hepatitis you have (B, C, or another type) and whether it is an acute or chronic infection.

Ask how long you may have had the disease and what type of symptoms your doctor wants you to watch for.

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