Viral hepatitis Flashcards
Explain the structure of a virus
- All viruses contain nucleic acid, either DNA or RNA (but not both), and a protein coat (capsid) that encases the nucleic acid
- Smaller than cells of living things
Explain the lytic and lysogenic cycle of viruses
- Lytic: Binds to receptors on host cell and injects its DNA/ RNA into it. Other times, the virus can be taken in by the cell (endocytosis). The virus overtakes the hosts machinery and continually replicates within the cell. Eventually, the cell burst and the virus leak out to infect other cells (the host cell dies)
- Lysogenic cycle: The virus integrates its genetic material into the hosts DNA. The virus recruits repressor genes to stop expression of its genes. However, if the host is weakened in some way, these repressor genes will stop working. The host DNA will recognise it is damaged and try to repair itself by excising the viral DNA out, but this activates the virus. The virus is now ready to make copies of itself, lyse the cell and infect other cells.
List the 4 stages in the life cycle of a virus
- Viral entry: For the virus to reproduce it must enter cells of the host organism and use those cells’ materials. To enter the cells, proteins on the surface of the virus interact with proteins of the cell. A hole forms in the cell membrane, then the virus particle or its genetic contents are released into the host cell.
- Viral replication: Next, the virus takes control of the host cell’s replication mechanisms.
- Viral shedding: After a virus has made many copies of itself, the progeny leaves the cell. This is called shedding and is the final stage in the viral life cycle.
- Viral latency: Some viruses can “hide” within a cell, which means they evade the host cell defences. This hiding is deemed latency. During this time, the virus does not produce any progeny, it remains inactive until external stimulisuch as light or stress prompts it to activate.
Which hepatitis virus is the only one to contain DNA as its genetic material?
What does this mean for the other types of hepatitis viruses?
Hepatitis B is the only virus that contains DNA as its genetic material
What does this mean for the other types of hepatitis viruses?
Hepatitis A, C, D and V contain RNA as their genetic material
Which hepatitis viruses are transmitted through the oro-faecal- enteric route?
- Hepatitis A
* Hepatitis V
Which hepatitis viruses do not have a carrier state? (asymptomatic people)
What does this mean for other hepatitis viruses?
Hepatitis viruses that do not have a carrier state (asymptomatic people):
• Hepatitis A
• Hepatitis V
What does this mean for other hepatitis viruses?
• Hepatitis B, C and D do have carrier states (asymptomatic people)
Which hepatitis viruses eventually result in chronic inflammation?
What does this mean for other hepatitis viruses?
The hepatitis viruses that result in chronic inflammation are:
• Hepatitis B
• Hepatitis C
• Hepatitis D
What does this mean for other hepatitis viruses?
Hepatitis A and Hepatitis V only result in acute inflammation
Which hepatitis viruses eventually result in complications (carcinomas)?
What does this mean for other hepatitis viruses?
The hepatitis viruses that result in complications like carcinomas are:
• Hepatitis B
• Hepatitis C
• Hepatitis D
What does this mean for other hepatitis viruses?
Hepatitis A and Hepatitis V do not result in carcinomas
Which hepatitis viruses do not have a vaccine?
- Hepatitis C
* Hepatitis V
Out of the two, state which hepatitis is more common.
• Hepatitis B
• Hepatitis C
• Hepatitis B
Explain the structure of the hepatitis B virus. Mention: • Hepatitis B surface antigen (HBsAg) • Hepatitis B core antigen (HBcAg) • Hepatitis B e antigen (HBeAg)
The virus consists of:
1. DNA
- HBV DNA polymerase (creates DNA molecules during replication)
- Hepatitis B surface antigen (HBsAg):
• A protein on thesurfaceofhepatitis Bvirus
• Detected in high levels in serum during acute or chronichepatitis Bvirus infection
• Indicates that the person is infectious - Hepatitis B core antigen (HBcAg):
• Surrounds the nucleocapsid (encloses the viral DNA) - Hepatitis B e antigen (HBeAg)
• A pre-core protein which is released in the blood stream by HBV infected hepatocytes
Discuss how Hepatitis B infects the liver cells
- The virus virus enters the cell by binding to a receptor hepatocytes
- Once in the cell, the virus releases its DNA which enters hepatocyte nucleus
- In the hepatocyte nucleus, the viral DNA is converted to cccDNA (which is like their version of a relaxed chromatin structure DNA)
- cccDNA is transcripted to form mRNA and RNA
- Viral proteins such as HBsAg, HBcAg and the HBeAg proteins are transcripted and produced
- The virus is eventually assembled after transcription and translation
- These copies of the virus are released from the liver cell membrane into the bloodstream and from there can infect other liver cells and thus replicate effectively
- Sometimes its viral proteins may be released like their HBsAg/ RNA molecules
- Infected hepatocytes will express surface antigens to inform the immune system of its infection
Discuss how Hepatitis B is mainly transmitted
- High: blood, serum, wound exudates
- Moderate: semen, vaginal fluid, saliva
- Detectable: urine, faeces, sweat, tears, breast milk
Most common:
• Perinatal/vertical (transmitted from mother to child): high endemicity regions
• Blood or other body fluids: parenteral/percutaneous, sexual. Low endemicity regions
Discuss how Hepatitis C infects the liver cells
- Hepatitis C is taken into the cell where it releases its RNA
- Once it enters the cell, the RNA is translated and replicated (in the Endoplasmic reticulum ER)
- Viral proteins are made
- The viral proteins are assembled to form the virus
- The virus is then released from the cell
Discuss how Hepatitis C is mainly transmitted
Parenteral exposure • Injecting drug use • Blood transfusion prior to 1990 • Needle stick injury (3%) • Tattoos, body piercing, shaving etc
Other
• Mother to child: 2-5% (15% if HIV co-infection)
• Sexual (1-2%)
