DERS 05 - GIT Infections 2

Question 1

Answer the following about hepatitis B virus (HBV):

• Enveloped?
• Shape?
• Genome type?
• Stability?
• Structure?

Answer 1

• Enveloped, spherical, with a partial dsDNA genome
• Stable at low pH, freezing temps, and in the presence of detergents and moderate heat
• Envelop contains 3 glycoproteins/surface antigens: S, M, L
• Inner nucleocapsid containg genome and viral Polymerase
  *

Question 2

What is HBV’s primary method for evading the immune system?

Answer 2

The majority of the viral proteins produced aren’t used for making virions. Instead, they are released as is, vastly outnumbering the virions and acting as decoys

Question 3

Describe the unique genome of HBV and the proteins coded by it

Answer 3

It only codes for 4 mRNAs and 1 full-length pre-genomic RNA. The 4 mRNAs code for many proteins by use of different ORFs:

• ORF P - viral polymerase - has DNApol, RT, & RNase H activity
• ORF S - HBV surface proteins - HBsAG (S,M,L), and Pre-S (viral attachment)
• ORF C - HBcAG (nucleocapsid protein) and HBeAG (unknown function)
• ORF X - HBx protein - transactivator that helps establish in vivo infection

Question 4

Detail the HBV life cycle

Answer 4

1. Pre-S proteins attach to hepatocytes for endocytosis
2. After endocytosis, membrane fusion occurs, releasing the nucleocapsid, which enters the nucleus
3. Host DNApol converts the viral partial dsDNA into complete dsDNA, called cccDNA (covalently closed circular)
4. Host DNApols the 4 mRNAs and 1 pre-genomic RNA
5. Host machinery makes viral particles which self-assemble
   
   1. HBcAg forms capsid
   2. S, M, and L proteins (HBsAG) form envelope
6. vPol uses its RT activity and the pre-genomic RNA to make one negative sense cDNA
7. vPol RNase H activity degrades the pre-genomic RNA
8. vPol DNApol activity partially copies the negative sense cDNA, making the complete partial dsDNA viral genome

Question 5

Facts to know about HBV epidemiology

Answer 5

• HBV is worldwide
• It is classified into 8 genotypes (A-H) and subgenotypes which are prevelant in different parts of the world and require different treatment

Question 6

Facts to know about HBV transmission

Answer 6

Extremely infective - one virion is enough to establish infection

Transmission is via blood or unportected sex

Question 7

Are hepatitis B infections acute or chronic? Which populations to affect the most? What can an HBV infection lead to?

Answer 7

Both

• Acute (<6mo) infections typically affect adults
  
  • Acute infections almost always resolve
  • Fulminant hepatitis can develop, which is fatal
• Chronic infections typically affect infants and is usually contracted from the mother during birth (vertical transmission). Chronic infections can develop several ways:
  
  • Asymptomatic
  • Chronic persistent
  • Chronic active - develops into liver failure, cirrhosis, and hepatocellular carcinoma.

Question 8

What are the clinical features of an acute HBV infection

Answer 8

• Fever, rash, and arthritis is sometimes seen before any other symptoms
• Typically preicteric and icteric symptoms

Question 9

Describe the pathogenesis of HBV

Answer 9

1. HBV does its thing within the cell
2. MHC-I present viral antigens which CD8+ T cells recognize, resulting in them doing two primary things
   
   1. Kill the HBV infected cell
   2. Initiate nonspecific inflammatory response by releasing TNFα and Interferon gamma
3. This all causes disruptions in cell signaling and destruction of p53, which leads to more cell necrosis and possibly clonal expansion of a particular cell type, resulting in hepatocellular carcinoma.

Question 10

Describe how HBV is diagnosed

Answer 10

• Qualitative and quantitative detection of the viral antigens HBsAG, HbeAG, and HBcAG; and of antibodies against HBs an HBc
  
  • This is done using various immunoassays and qRT-PCR
• Blood work for ALT/AST/LDH/AP to measure extent of liver injury
• Liver biopsy

Question 11

What is the HBV window period and why is it important?

Answer 11

During an HBV infection, there is an abundance of HBsAG (the decoy particles). Because of this, the few Anti-HBs particles made become complexed with a lot of HBsAG, making it undetectable. There is a window period, during convalescence, where the HBsAg levels have fallen to the point where neither they nor the anti-HBs particles are detectable (because of the complexing)

This is important because while a positive HBsAg indicates infection, a negative result may be a FN. Therefore, the IgM anti-HBc is tested for to determine the presence of an acute infection (which is when the window period would be)

Question 12

Write out the test result for the following in a HBV susceptible, immune due to natural infection, immune due to HB vaccine, acutely infected, and chronically infected individual:

• HBsAg
• anti-HBc
• IgM anti-HBc
• anti-HBs

Answer 12

Question 13

Facts to know about HBV treatment and prevention

Answer 13

• Prevention
  
  • Subunit vaccines
  • Immune globulin given after infection but before Sx
  • Screening blood supply
  • Eliminate risky behavior
• Treatment
  
  • Interferon and/or
  • Antivirals-polymerase inhibitors (nucleoside/nucleotide analogs)

Question 14

What kind of genome does HDV have? List the proteins it has and what they’re used for.

Answer 14

• -ve sense ssRNA in a rod shape due to extensive base pairing
• HDV utilizes HBsAG proteins for its evelope, which means HDV infections cannot occur with HBV coinfection or chronic infection
• HDV nucleocapsid proteins are:
  
  • small delta antigen (S-HDAg), which helps control genome replication
  • large delta antigen (L-HDAg), which is required for virion assembly

Question 15

Describe the HDV life cycle in the level of detail we need to know.

Answer 15

1. HDV binds to hepatocyte receptor and is endocytosed
2. HDV is uncoated in the cytoplasm and the genome is translocated in the nucleus
3. Host RNApol 1 and 2 produce the +ve and -ve sense viral RNA
4. +ve sense strand is used to make the HDV viral antigens
5. The -ve sense strand complexes with the HDV viral antigens and moves into the cytoplasm
6. Virion production is complete when HBsAg particles form an envelope around the HDV capsid

Question 16

What are the clinical manifestations of HDV?

Answer 16

Depends on the type of infection

• Coinfection - similar Sx to HBV with the Sx being more severe at first - low risk of chronic HDV infection
• Superinfection - HDV infection of a chronically infected HBV patient - even more severe HBV Sx with a high risk of the development of chronic HDV infection
• Fulminant hepatitis - rapid development of acute liver injury with severe impairment of function

Question 17

How is HDV transmitted, diagnosed, treated, and prevented?

Answer 17

• Transmission is identical to HBV
• Diagnosis is done by testing for anti-HDAg, HDV RNA, and HDAg (acute phase)
• Treatment - none that are 100% effective but Interferon alpha helps
• Prevntion with HBV vaccination

Question 18

What are the HDV serology results used to diagnose coinfection and superinfection?

Answer 18

Coinfection - IgM anti-HBc & anti-HDV

Superinfection - IgG anti-HBc & anti-HDV

Question 19

What is a trematode? What are the aka? List the ones we need to know and the pathologies they cause.

Answer 19

A parasitic flatworm, aka fluke, that lays eggs

• Fasciola hepatica (liver fluke or sheep liver fluke) and Fasciola gigantica (giant fluke)
  
  • Hepatic fibrosis and necrosis, cholangitis (inflammation of the bile duct system), biliary obstruction, biliary cirrhosis
• Clonorchis sinensis and Opisthorchis sinensis (oriental liver fluke)
  
  • Cholangitis, biliary hyperplasia/obstruction, cholangiocarcinoma

Question 20

Describe the basic life cycle of Fasciola spp.

Answer 20

1. Eggs are shed in water, invade a snail, and develop into cercariae
2. Cercariae leave snail and encyst onto aquatic vegetation as metacercariae
3. Mammals ingest the metacercariae
4. Metacercariae excyst in the duodenum, migrate through the intestinal wall, peritoneal cavity, and liver parenchyma into biliary ducts where they develop into adult flukes
5. Adult flukes lay eggs that are shed in the mammal’s feces

Question 21

What are the clinical manifestations of Fascioliasis (a Fasciola spp infection)

Answer 21

There are 4 phases and only 15% of people become symptomatic

1. Incubation period (following ingestion) - days to months
2. Acute Phase (migration of larvae) - 2-4 months
   
   1. Generalized allergic/toxic reactions, fever, RUQ or generalized abdominal pain, hepatomegaly, loss of appetite, nausea, diarrhea
3. Latent phase (parasite maturation) - months to yrs - asymptomatic
4. Chronic Phase
   
   1. biliary colic, nausea, intolerance of fatty food, RUQ/Epigastric Pain, obstructive jaundice, pruritus, biliary lithiasis

Question 22

How is Fascioliasis diagnosed? How prevalent is the disease?

Answer 22

• Diagnosis - microscopy of ova in stool
• Disease is found worldwide, no continent is free from fascioliasis

Question 23

Describe the basic life cycle of Clonorchis sinensis/Opisthorchis sinensis

Answer 23

1. Eggs are shed in water, invade a snail, and develop into cercariae
2. Cercariae leave snail, enter fish, and encyst as metacercariae
3. Mammals ingest fish
4. Metacercariae excyst in the duodenum, migrate through the intestinal wall, peritoneal cavity, and liver parenchyma into biliary ducts where they develop into adult flukes
5. Adult flukes lay eggs that are shed in the mammal’s feces

Question 24

What are the clinical manifestations of C. sinensis?

Answer 24

• Mild infections are asymptomatic
• Severe Infections - fever, diarrhea, epigastric pain, hepatomegaly, anorexia, occasional jaundice, biliary obstruction, cholecystitis (gallbladder inflammation), cholelithiasis (gall stones), impaired liver function
• Chronic Infections - adenocarcinoma of bile duct

Question 25

Where is C. sinensis usually seen?

Answer 25

* Asia - korea, china, taiwan, vietnam, japan, asian russia * USA - asian immigrants/refugees

Question 26

Answer 26

E