Hepatitis: Etiology

00:00 So let's talk about the virology itself. First, hepatitis A virus. This is a spherical enveloped positive-sense RNA virus, one of the picornaviruses. When you talk about a positive-sense virus, that means that it already can function as messenger RNA and it can already infect the ribosomes of human cells. Humans are the only important reservoir and as I mention this is spread person to person by the fecal oral route and this virus remains infectious in the environment for long periods of time and as you might expect outbreaks are associated with food handlers. It used to be that the consumption of raw or rare shellfish was associated with large outbreaks of hepatitis A but no longer. Now hepatitis B virus on the other hand is a small DNA virus and there are huge, and I mean huge, quantities of this virus in the blood of people who are newly infected and they've not only got whole virus, which are these spherical structures that you see here, but there are also some filamentous structures. It's the whole virus particles that are the infectious particles but hepatitis B surface antigen is present on all of it and as you might expect if you are stuck with a needle that's been in a person who's got hepatitis B, you're very likely to be exposed to this virus. So contaminated syringes and needles are an important way of transmission. So think about, for example, IV drug users.

02:12 Hepatitis C virus is a spherical enveloped, positive-sense RNA virus and it's a member of the Flaviviridae. These viruses rather, I hate to call it, unstable but it mutates fairly rapidly and so you have dozens of what we call quasispecies detected over time which are different from the strain that might have infected the person, which is part of one of the challenges of why it's hard to treat. Now, hepatitis D virus is a small DNA virus and because it's a rather defective virus it's dependent on the presence of hepatitis B for replication. So if a person doesn't have hepatitis B, the patient can't have hepatitis D. Hepatitis E virus is a member of the Hepeviridae family, it's a hepevirus. It's also a single-stranded positive-sense RNA virus which can function as messenger RNA with our ribosomes. There are 4 genotypes, hepatitis E virus 1 through 4. Genotypes 1 and 2 you find in Asia, Africa and Mexico and have caused epidemic hepatitis there. It's transmitted by waterborne into the fecal oral route, kind of like hepatitis A.

03:48 Genotypes 3 and 4 found in Europe, North America and Asia and it is related to the swine viruses and can cause infection in swine and humans turn out to be an accidental host.