This lesson will cover the structure, mode of transmission and diseases associated with the Hepadnaviridae family of viruses, including the hepatitis B virus, hepatocellular carcinoma, cirrhosis and oncogenesis. We’ll also cover the hepatitis D virus and its effects on your body.
The Hepadnaviridae Virus Family
There are all sorts of nasty things that can damage your body. In the case of the liver, long-term alcohol consumption, drug abuse or toxins are among the many things that can damage the liver beyond repair. However, there are also some viruses that can do some liver damage as well.
What’s really cool about the virus family we’re going to talk about in this lesson, the Hepadnaviridae virus family, is that one type of virus in this family spells double trouble in three different ways.If that didn’t catch your attention for this lesson, then how about this: this virus, right now, affects more people than the entire population of the United States, has at some point in their life infected about two billion people worldwide and kills upwards of a million people every year.
Structure and Transmission
Hopefully, that was enough to grab your attention as we move into the details of this family as a whole.When it comes to this family’s genome, the viruses of this family have partially double-stranded DNA that is circular in shape. With respect to the structure of the viruses in the Hepadnaviridae family, they are icosahedral in shape, and they are enveloped. This means that because of their envelope, they are rather easily destroyed. This seems counterintuitive, since the envelopes we send in the mail are meant to protect what’s inside of them.
However, in the case of a virus, their envelope is very fragile, and one little puncture wound can cause it to tear apart, killing the virus inside. The things that can cause a puncture in the envelope are many, ranging from disinfectants to dry air. Think of it this way – when there’s dry winter air around, your skin can crack. Well, the envelope of a virus will also crack under dry air, and this will cause it to die. But, we don’t care; these are nasty viruses anyways.These nasty viruses spread using many different means to one end.
It can get you through contaminated blood transfusions, sexual intercourse, the re-use of contaminated needles or syringes and during childbirth.Basically, using one way or another, it spreads through contaminated body fluids, namely the blood. This is only one reason why being a vampire is a really bad idea!
The single most important virus in this family is the hepatitis B virus, or HBV for short. People who have had this virus for a long time in their liver cells, called hepatocytes, have a characteristic ground glass appearance to their liver cells when looked at under the microscope.
You might be wondering why we even look for HBV in the liver anyways. Well, it’s because HBV causes, not surprisingly, hepatitis B. And hepatitis B is a condition caused by the hepatitis B virus that causes severe inflammation of the liver.What happens is that your body’s immune system recognizes the fact that this virus has infected your liver cells.
Rightfully so, like any good defender, your immune system tries to kill the virus. However, part of our body’s defense mechanisms aren’t all that well-designed.You see, the cells involved in trying to kill off the virus spread about all sorts of enzymes and chemicals that cause inflammation. But, they do so indiscriminately. They cannot target the virus alone without hurting your own liver cells in the process. So, as your immune system tries to kill the virus via the inflammatory processes, it ends up killing your liver, and therefore you, in the end as well.
Bummer. Certain parts of the immune system are basically like a really drunk boxer who ends up punching everyone in his way, even his best friends.
Cirrhosis and Hepatocellular Carcinoma
As I mentioned all the way in the beginning of this lesson, this virus has three separate double-whammies that affect many people around the world. The first is that it not only causes inflammation of the liver, but it also causes cirrhosis, which is a disruption of normal liver function and structure as a result of prolonged liver damage.You may have heard this term before, as alcoholics are predisposed to getting this condition. Unlike many other organs of your body, the liver is actually able to regenerate if damaged, but it does so with very poor efficiency.
This causes the formation of discombobulated masses of liver cells that cannot function together. It’s almost entirely useless.In addition, the prolonged inflammation caused by our body’s immune response to the virus essentially cuts the liver apart. Your body tries to heal these wounds through a process called fibrosis, which is basically the formation of scar tissue. Think of it this way – if you cut your skin really deeply, you’d get a scar.
Well, this virus cuts deep and causes an ugly, painful and non-functional scar to appear in the place of functional liver cells.But wait! There’s more! I did say there are two more whammies coming up. If you thought getting a liver full of scars was bad enough, you better think again. Some viruses can cause cancer some of the time. That’s right, cancer! HBV is one of those viruses.
It causes something called a hepatocellular carcinoma, which is the most common form of liver cancer.The prefix hepato refers to the ‘liver;’ therefore, hepatocellular referrers to ‘liver cells.’ Now it should also make sense why this family is called Hepadnaviridae. It gets the hepa from hepato because it affects the liver so much.You might be wondering how in the world a virus causes cancer. I’ll be happy to indulge you. In general, a virus may use its genome to start a process called oncogenesis in the cell it infects.
Oncogenesis is defined as the creation of a tumor or cancer. What basically happens is that the genes inserted by a virus into a host cell’s genome can trigger changes that lead to uncontrolled growth of a previously healthy cell. This process is only one component in the formation of cancer.Nevertheless, don’t get confused between a tumor and a cancer. A tumor is just a swelling of any sort, and it can be benign, or relatively unharmful.
However, other tumors can be or eventually become malignant, or cancerous.With that in mind, another way by which a virus can cause cancer is by triggering the inflammatory process I mentioned before. Decades worth of inflammation caused by anything at all, not just a virus, can actually cause a cell, such as a liver cell, to become cancerous. It is presumed that the molecules that cause the inflammation lead a normal cell to incur lots of damage to its DNA, which over time leads to uncontrolled cell growth.
Hepatitis D and Vaccination
As if that wasn’t enough, the third and final double-whammy HBV causes is through something called the hepatitis D virus. This is a virus that increases the complications associated with hepatitis B. The hepatitis D virus is not part of the Hepadnaviridae family and is currently not assigned to any virus family, but it still causes a big mess.
In essence, the hepatitis D virus must infect simultaneously with HBV or infect after HBV has already established an infection in order to function properly. Over time, it will exacerbate the effects of HBV, leading to a higher likelihood of developing cirrhosis, cancer and liver failure.There is no vaccination for hepatitis D. However, hepatitis B can be prevented by getting a series of vaccines. This vaccine may be a really good idea because infection with the hepatitis B virus may infect a person chronically, that is, for a long time, and it is this chronic infection that causes a lot of the problems we discussed in this lesson.
Well, I hope that all of the information in this lesson hasn’t scarred you like this virus can scar your liver. Let’s go over the important points one more time.
The single most important virus in the Hepadnaviridae family is the hepatitis B virus, or HBV for short, which causes hepatitis B. Hepatitis B is a condition caused by the hepatitis B virus that causes severe inflammation of the liver.Don’t forget that the hepatitis D virus is a virus that increases the complications associated with hepatitis B. HBV alone or with the hepatitis D virus can cause cirrhosis, which is a disruption of normal liver function and structure as a result of prolonged liver damage, and hepatocellular carcinoma, which is the most common form of liver cancer.
It may cause the latter to occur by imposing its gene structure into that of our liver cells, causing a process called oncogenesis to occur. Oncogenesis is defined as the creation of a tumor or cancer.
After completing this lesson, you may be able to:
- Evaluate the structure of the Hepadnaviridae virus family and discuss how it is transmitted
- Give insight as to how hepatitis B affects the liver
- Pinpoint how and which Hepadnaviridae viruses can cause cirrhosis and hepatocellular carcinoma
- Know the definition of oncogenesis