Unit 4 - Hepatitis Virus

Question 1

Describe the History of Viral Hepatitis.

Answer 1

Hepatitis—inflammation of the liver

• Classic symptom—jaundice
• Caused by a number of viruses and sometimes alcohol or prescription drugs

Hepatitis epidemics in history

• War: Crowding and unsanitary conditions of military encampments created an ideal environment for hepatitis A viruses to be transmitted.
• Camp jaundice and outbreaks recorded:
  
  • Napoleonic Wars
  • U.S. Civil War—camp jaundice
  • WWI—trench warfare
  • WWII—serum hepatitis (via vaccination) and infectious hepatitis (contaminated battle fields)

Question 2

What is hepatitis C and U.S. Military veterans?

Answer 2

8%–9% of Veteran Affairs (VA) medical center patients are positive for hepatitis C antibodies.

• Vietnam era of hepatitis epidemics
• Combatants survived multiple blood transfusions
• Intravenous heroin use
• Sharing of razors and other non-sterile instruments
• History of tattooing
• History of prostitution
• Blood/bodily fluid exposure to healthcare and combat personnel
• Receipt of contaminated immunoglobulin for hepatitis A prior to hepatitis C screening

Question 3

What is epidemiology?

Answer 3

• Yellow fever virus, herpes simplex viruses, cytomegaloviruses, and Epstein-Barr virus can cause hepatitis.
• A group of unrelated pathogens termed “hepatitis viruses” cause the vast majority of virally-induced hepatitis cases.
• The focus of this lecture is on the hepatitis viruses.

Question 4

What are the hepatitis Virus?

Answer 4

Each starts with a letter with the exception of the newly identified transfusion transmission virus (TTV) and SEN viruses.
Hepatitis A
Hepatitis B
Hepatitis non-A, non-B viruses
Hepatitis C
Hepatitis D
Hepatitis E
Hepatitis G

Question 5

What are the Clincial Features of hepatitis A?

Answer 5

• Most outbreaks associated with contaminated food or water supplies
• Shellfish may become contaminated with sewage and may concentrate and retain viruses.
• Major mode of transmission: fecal–oral
• Average incubation period: 30 days
• Adults experience signs and symptoms more often than children.
• Pregnant women at increased risk

Question 6

What are the onset symptoms of HAV?

Answer 6

Fatigue

Abdominal pain

Loss of appetite

Nausea and vomiting

Dark Urine

Jaundice

Question 7

What is Jaundice

Answer 7

• Yellow color in the skin, muscous memberanes, or eyes
• Occurs when liver is not functioning properly
• Yellow pigment is from bilirubina byproduct of old red blood cells.

Question 8

What is Hepatitis B (HBV)?

Answer 8

• Relatively rare in developed countries
• Endemic areas: major model of spread is mother (carrier) to infant (blood of infected mother enters fetus)
• Other high-risk groups
  
  • IV drug users
  • Hemodialysis patients
  • Persons with multiple sex partners
  • Institutionalized patients
  • Healthcare workers
• Average incubation period is 80 days.
• 30% of individuals have no signs and symptoms
• If symptoms occur, they are similar to hepatitis A but with joint pain.
• Chronic hepatitis B infections occurs in 5%–10% of cases.
• Chronic infections lead to:
  
  • Cirrhosis of liver
  • Hepatocellular carcinoma (HCC) or liver cancer

Question 9

What is Hepatocellular (Liver) Cancer (HCC)?

Answer 9

• HBV DNA sequences are found in HCC tumor DNA
• Integration of HBV DNA occurs in breaks in cellular DNA of hepatocytes (liver cells)
• Chronic HBV infections cause ongoing inflammatory responses and oxidative damage to chromosomal DNA of hpatocytes
• Death from chronic liver disease result in 15%-25% of individuals
  *

Question 10

What is hepatitis C?

Answer 10

Prior to 1989: Cases of hepatitis of unknown etiology (hepatitis A and B viruses ruled out)
These cases were referred to as “hepatitis non-A, non-B” viruses.
1989: Scientists found a new viral genome present in infectious plasma.
Eventually the new viral pathogen was identified, as it was visualized by TEM, etc.

Question 11

What is the major public health problem with heaptitis C?

Answer 11

• “Silent epidemic”- many infected people show few or no signs of disease for years, even decades.
• Contaminated hemophilia blood products.
• HCV infection is common in the developed world.
• 4 million people in United States
• Up to 170 million people worldwide

Question 12

What is HCV transmission?

Answer 12

• Incubation period: 6–7 weeks
• Spread almost exclusively through blood contact
• Individuals who received blood products before 1992 are at risk for contracting HCV.
• Donated blood screening for HCV did not begin until 1992.
• 80% of those infected are asymptomatic; if signs or symptoms are present, they resemble other hepatitis infections.
• Between 55% and 85% of infected persons experience a chronic infection, resulting in chronic liver disease.
• Chronic infection can lead to cirrhosis of the liver and HCC in 5%–20% of infected persons.
• April 2013: Oral surgeon in Oklahoma cited for sterilization violations
• 3,200 patients screened for HIV, HBV, and HBV
• 57 patients tested positive for HCV
• 3 patients tested positive for HBV

Question 13

What is Hepatitis D (HDV)?

Question 14

What is Hepatitis E (HEV)?

Answer 14

• HEV is endemic in the developing countries of Asia and Africa.
• HEV is rare in industrialized nations.
• Sporadic cases have been reported in the United States, France, Italy, and the United Kingdom
• Mode of transmission: similar to HAV (fecal–oral route)
• Person-to-person transmission rare
• Incubation period: 40 days (average)
• Outbreaks are often associated with fecally contaminated water supplies.

Question 15

HEV causes a more severe Illness than HAV

Answer 15

• HEV causes 1%–3% mortality (general population).
• HEV causes 15%–25% mortality in pregnant women.
• Some evidence that hepatitis E may be a zoonotic disease (from pigs)
• Human HEV isolates are genetically similar to pig HEV strains isolated from pigs in the United States.
• Pig HEV can infect non-human primates

Question 16

What hepatitis agents are not A-E?

Answer 16

Hepatitis G (HGV)

• Isolated from plasma of a surgeon in 1996
• Clinical significance unclear

Sentinel virus (SEN)

• Identified in 2000
• May be responsible for the 10% of transfusion-associated hepatitis with no known origin

Transfusion transmission virus or torque teno virus (TTV)

• Apparently identified in Japanese post-transfusion hepatitis patients in 1997

Question 17

What are the Lab Diagnosis of viral hepatitis infections based on?

Answer 17

• Symptoms (jaundice)
• Blood tests for liver enzymes
• Viral antibodies (e.g., IgM)
• Viral genetic material (e.g., RT-PCR or PCR

Question 18

What are the blood samples that are tested for Two Liver enzymes?

Answer 18

Aspartate aminotransferase (AST)
 Alanine aminotransferase (ALT)

These enzymes are normally found in the liver but spill into the blood if the liver is damaged, thus raising the enzyme levels in the blood.

Nucleic acid tests (PCR, RT-PCR) to detect viral genomes are only available in specialized laboratories.

Question 19

What is Viral hepatitis diagnosis?

Answer 19

• Patients with chronic hepatitis are harder to diagnose because these patients do not have nausea or jaundice until the liver damage is very advanced.
• Serology
• detection of IgM antibodies) is used to detect HAV, HBV, and HCV.
• Antibodies against HBV surface antigen (HBsAg) or HBV core antigen (HBCAg)

Question 20

What is the Screening of the Blood Supply for viral hepatitis agents?

Answer 20

American Red Cross began screening for:
1971: Hepatitis B surface antigen
1987: HBcAg antibodies
1986–2003: elevated alanine aminotransferase levels
1990: HCV antibodies
1999: nucleic acid test for HCV genomes
Blood is not screened for other hepatitis viruses.
U.S. blood supply is one of the safest in the world.

Question 21

What is the Pathogeneisis of Chronic hepatitis?

Answer 21

Chronic hepatitis
Active inflammation of liver (liver biopsy)
Persists for more than 6 months
Increased alanine aminotransferase (ALT) in serum
Hepatitis B, C, D, and G viruses cause chronic hepatitis infections.
Chronic liver damage may result in cirrhosis.
Formation of fibrous tissues, nodules, scarring that interferes with liver function and blood circulation
Late complication of chronic hepatitis is HCC.

Question 22

What is the Hepatitis Virus Life Cycle?

Answer 22

• Hepatitis viruses belong to 5 different families.
• Two of the hepatitis viruses are unassigned.
• Five of the eight viruses (hepatitis viruses A–E) have been well characterized.

Question 23

What is the Virus Structure for Hepatitis A-E?

Answer 23

Spherical shaped and icosahedral symmetry
28–50 nm in diameter
Enveloped (B, C, D) or non-enveloped (A or E)
Hepatitis B, C, and D are sensitive to many physical and chemical agents
Hepatitis A viruses are acid- and bile-resistant
Hepatitis A can remain infectious on inanimate surfaces for a month

Question 24

What is involved in Virus Replication?

Answer 24

Hepatitis viruses enter the bloodstream.
Carried to the liver
Infect the hepatocytes
As hepatocytes are damaged, liver cirrhosis and liver function are impaired.
Liver important in metabolism, filtration of toxins and waste, digestion (bile), and synthesis (amino acids, coagulation factors, etc.)

Question 25

Describe Hepatitis A.

Answer 25

* Very stable in the environment * **Naked** picornavirus * **+ssRNA** genome that is 7.5 kb in length * Viral genome and poly (A) tail at the 3′ terminus of the genome * 5′ end of the genome contains a non-translated region of hairpins and pseudoknots. * Hairpin structures act as internal ribosomal entry sites (IRES) that are necessary for cap-independent translation of the viral mRNA.

Question 26

What is involved in HAV mRNA Translation?

Answer 26

The +ssRNA viral genome acts directly as an mRNA for the synthesis of a large polyprotein. Similar to polioviruses (see Chapter 11) ## Footnote The polyprotein is processed by a viral 3C protease into structural and nonstructural proteins of the virus.

Question 27

What is involved in HAV genome Replication and Particle Assembly?

Answer 27

* A Viral RNA-dependent RNA polymerase encoded by the 3D gene synthesizes new - ssRNA intermediates used to create progeny genomic +ssRNAs * Newly assembled particles are transported to the surface of heptocytes and are exported

Question 28

Describe Hepatits B virus

Answer 28

Initial characterization of hepatitis B infections * Baruch Blumberg collected blood samples from hemophiliacs (**exposed to many donor serum proteins).** * 1963: Antibodies in the serum of a New York hemophiliac reacted with an antigen present in the blood of an Australian aborigine infected with hepatitis. * **Australia antigen was the hepatitis B surface** antigen (HBsAg). * Further experiments by David Dane led to the discovery of the **Dane particle** (complete infectious hepatitis B virus).

Question 29

What are the Three types of Hepatitis B Particles present during infection during Infection?

Answer 29

* Most abundant HBV particle in carriers is a spherical 17–25 nm particle. * Less numerous are non-infectious filamentous particles that are up to 200 nm in length. * Dane particles (infectious) are 42 nm in diameter, and enveloped. * Dane particle contains the viral DNA polymerase (RT), protein kinase C, and heat shock 90 protein associated with the viral genome.

Question 30

What is the HBV genome?

Answer 30

* Ciricular **_partially dsDNA_** * Full length strand is 3.2 kb * Shorter strand is 1.7 kb length * Uses a replication strategy common to retroviruses * replicate through an RNA intermediate via reverse transciption

Question 31

Describe HBV attachment and Entry?

Answer 31

* Host receptor is unknown; possibilities include: * Transferrin receptor * Human liver endonexin * Asialoglycoprotein receptor molecule * Hepatitis B grows poorly in cell culture—difficult to study molecular mechanisms of viral attachment and entry * After fusion and entry—uncoating step

Question 32

What is Uncoating/Genome Replication?

Answer 32

* During uncoating, viral cores are released into the cytoplasm. * Genome uncoats and enters the nucleus through the nuclear pores. * Host enzymes ligate the ends of the genome. * DNA synthesis is completed; gaps are repaired in both DNA strands. * Genome is now a closed circular plasmid-like dsDNA molecule called an episome. * The episome replicates independently of the host chromosome. * HBV DNA does not integrate into the host chromosome (not integrase activity).

Question 33

What is the HBV Episome?

Answer 33

Acts as a template for two classes of viral transcripts: * Viral pregenomic RNA transcripts * Genomic RNA transcripts transcribed by the host’s RNA polymerase II HBV genome has compact coding organization * 4 promoters * 2 enhancers * 4 partially overlapping ORFs translated into 7 proteins (see Table 17-4) * Several binding sites on genome recognized by transcription factors

Question 34

What is the coinfection of HBV and HDV?

Answer 34

* HDV is a defective virus. * Requires the presence of a “helper” HBV to assemble mature virions * The surface or outer coat of HDV consists of HBsAgs. * HDV is associated with chronic hepatitis. * HDV probably uses the same cellular receptor as HBV.

Question 35

What is the HDV genome replication?

Answer 35

* RNA genome has intramolecular basepairing. * During uncoating, the viral envelope is removed inside of an infected cell and is targeted to the nucleus. * The cellular RNA polymerase II and other host factors replicate the viral genome. * The HDV genome is a ribozyme- cleaves itself. * Genome replication occurs via a rolling circle mechanism similar to that of viroids (see Chapter 19).

Question 36

What is the hepatitis C virus (HCV)?

Answer 36

* Icosahedron-shaped, enveloped virus * +ssRNA flavivirus * Not much information known about HCVs’ ultrastructure * The only flavivirus that is not transmitted by arthropods * Similar to picornaviruses (e.g., poliovirus) except that HCV particles are enveloped * Viral nucleic acid cloned in 1989

Question 37

What is the HCV genome?

Answer 37

* 9.2 kb in length * Contains an internal ribosome entry site (IRES) * One long ORF that encodes a polyprotein precursor that is cleaved into nonstructural and structural proteins by cellular and viral proteases * Viral genome is translated by host ribosomes * NS5b gene encodes its own RNA-dependent RNA polymerase * Viral entry receptors: clathrin, CD81, SR-B1 * IFN resistance correlated with the HCV E1 and E2 proteins

Question 38

What is Hepatitis E genome (HEV)?

Answer 38

* +ssRNA genome * Clinically indistinguishable from HAV infection * HEV particles less stable than HAV * Non-enveloped, icosahedral-shaped * 32–34 nm in diameter * 7.2 kb genome (contains short 5′ and 3′ noncoding regions) * 3′ end contains a poly(A) tail

Question 39

Describe the HEV genome?

Answer 39

Lack of molecular biology information available No suitable cell culture system to propagate HEV Three overlapping ORFs ORF1 (non-structural proteins like protease and replicase) ORF2 (structural proteins; capsid) ORF3 (small phosphoprotein of unknown function)

Question 40

What is tht ePathophysiology of chronic hepatitis virus infections?

Answer 40

* The enveloped viruses (HBV, HCV, HDV, HGV) cause persistent and chronic infections. * These viruses possess immune evasion strategies. * HBV reactivation in livers from HBV-immune donors * HBV likely exists in hepatocytes in a latent form for a long time * Liver damage caused by HBV and HCV may result from an autoimmune reaction directed against hepatocyte antigens initiated by viral infection.

Question 41

What is the management and prevention of hepatitis A-E virus?

Answer 41

Hepatitis A management * No specific treatment * Supportive care Prevention: handwashing and proper sanitary disposal of human feces * Passive immunity (immunoglobulin) 85% effective in preventing disease if given with 2 weeks of exposure HAV vaccine: formalin-inactivated, cell culture produced whole-vaccines * Injections at 0, 6, and 12 months in individuals \> 2 yrs old * Live-attenuated vaccines being tested

Question 42

What is involved in HBV management and Prevention?

Answer 42

* Basic goal is to stop viral replication and prevent end-stage liver disease * Three licensed drugs to treat HBV * Interferon -2b (46% response rate; many side effects) * Lamivudine (RT inhibitor) * Adefovir dipivoxil (RT inhibitor) * Immunoglobulin used as an adjunct to HBV vaccine in preventing HBV transmission from an infected mother to fetus * 70-90% of infants born to HBeAg-positive mothers become infected at birth and develop chronic HBV

Question 43

What are the HBV Vaccines?

Answer 43

* Early vaccines were prepared by harvesting spherical particles from plasma of chronically infected individuals. * Particles purified and inactivated by heat, formaldehyde, urea, or pepsin * Subsequently, vaccine manufacturers used genetic engineering to express HBsAg in yeast. * Purified HBsAg self assembles into spherical particles resembling 17–25 nm particles found in the serum of people with chronic hepatitis. * Safe; noninfectious particle

Question 44

What are HBV Vaccine REcommendations by the CDC?

Answer 44

* Newborns should receive a birth dose before leaving the hospital * Children age 19 and under should recieve the HBV vaccine series * HBV accine is the first vaccine to prevent a cancer * Between 1990 and 2002 the incidence of heptatits B-related liver cancer decreased 67%.

Question 45

How is HCV managed?

Answer 45

85% of HCV infections progress to chronic liver disease No vaccine available HCV has a high mutation rate Current therapies to manage HCV infection: Pegylated interferon and Ribavirin (nucleoside analog) 75% cure rate, but takes up to 1 year and has debilitating side-effects Sofosbuvir (nucleotide analog); now in clinical trials 97-99% virus eliminated after 12 week treatment when combined with ribavirin Response to therapy is measured by levels of serum transaminases and detection of HCV RNA. Six main genotypes of HCV Certain genotypes respond better to treatment than others

Question 46

What is the breakthrough for a hepatitis C virus research?

Answer 46

1989: HCV discovered 2005: entire viral genome isolated and sequenced RNA inserted to human liver cell line (Huh-7.5 cells) Infectious particles produced for study

Question 47

What is HDV and HEV Management?

Answer 47

HDV infections maintained by reducing HBV replication * Interferon, lamivudine, adeovir * No immune globulin or HDV vaccine HEV infections usually self-limiting * Treatment is supportive * No immunoglobulin or HEV vaccine available * Focus on prevention