Microbiology Recall: Enveloped Dna Viruses

Front 1

What are three clinically relevant families of enveloped dsDNA viruses?

Back 1

1) Hepadenaviridae
2) Herpesviridae
3) Poxviridae

Front 2

What type of nucleic acid do Hepadna viridae contain in their genome?

What is their capsid geometry?

Do they contain an envelope?

Back 2

Incomplete circular dsDNA

Icosahedral

YES

Front 3

What is the main human pathogen of the Hepadnaviridae?

Back 3

Hepatitis B virus
Not all viruses causing hepatitis in humans are members of Hepadnaviridae.

Front 4

What is the viral DNA structure of HBV?

Back 4

Long, negative strand with a complementary short, positive strand.

Front 5

What are two unique characteristics of HBV replication?

Back 5

1) Use of an RNA intermediate
2) Use of revere transcriptase to create a template DNA strand inside the progeny capsid.
Hepadnaviridae are the only DNA viruses to replicate via an RNA intermediate.

Front 6

What enzyme creates the RNA intermediate?

Back 6

RNA polymerase II from the host cell.

Front 7

Where in the cell is the RNA intermediate synthesized?

Back 7

In the nucleus

Front 8

Where in the cell is the DNA template created by reverse transcriptase?

Back 8

In the cytoplasm

Front 9

What are the steps of HBV replication?

Back 9

1) Incomplete circular viral DNA moves into the nucleus
2) The virus produces complete circular DNA in teh nucleus
3) Viral DNA is transcribed into messenger RNA (mRNA) by host RNA polymerase II.
4) mRNA migrates to the cytoplasm where it is translated into proteins using host enzymes.
5) mRNA is reverse transcribed into a template strand by viral-encoded reverse-transcriptase enzyme
6) Template strand migrates into progeny capsid and is used to create a complementary DNA strand by host DNA-dependent DNA polymerase to form circular dsDNA progeny genomes.

Front 10

What is the Dane particle?

Back 10

Infectious HBV particle.

Front 11

What are the four proteins encoded by HBV?

Back 11

1) Hepatitis B surface antigen (HBsAg) encodes dy gene S.
2) Hepatitis B core antigen (HBcAg) encoded by gene C.
3) Protein X encoded by region X
4) Reverse transcriptase/DNA polymerase encoded by region P

Front 12

What is hepatitis B e antigen (HBeAg)?

Back 12

A truncated form of HBcAg associated with the HBV nucleocapsid that circulates in the serum

Front 13

What is the significance of HBeAg?

Back 13

Presence of HBeAg indicates increased transmissibility.

Front 14

What are three modes of HBV transmission?

Back 14

1) Blood-to-blood transmission (IV needles, infected blood transfusion)
2) Sexual transmission
3) Perinatal transmission, including breastfeeding.

Front 15

What is the risk of becoming infected with HBV, hepatitis C virus (HCV), or human immunodeficiency virus (HIV) from a needle stick with contaminated blood?

Back 15

20% chance of HBV infection
2% chance of HCV
0.2% chance of HIV infection

Front 16

What are the signs and symptoms of acute HBV infection?

Back 16

Jaundice, fatigue, nausea, vomiting, abdominal and joint pain, pruritus.

Front 17

What are the signs and symptoms of acute HBV infection?

Back 17

Elevated serum aminotransferases ([AST]/[ALT]), bilirubin, and alkaline phosphatase.

Front 18

What is the prognosis for a patient with acute hepatitis B?

Back 18

90% of patients clear infection
9% progress to chronic hepatitis
1% develop fulminant hepatitis and death

Front 19

What are three ocmplications of chronic HBV infection?

Back 19

1) Chronic hepatitis
2) Cirrhosis
3) Hepatocellular carcinoma

Front 20

Why is hepatocellular carcinoma common in chronic carriers of HBV?

Back 20

Chronic hepatocyte damage secondary to the immune response to the virus causes chronic cellular regeneration and an increased opportunity for mutagensis

HBV is not oncogenic by itself

Front 21

Coinfection with what virus increases the risk of chronic and fulminant hepatitis in people infected with HBV?

Back 21

Hepatitis D virus

Front 22

What type of virus is Hepatitis D virus?

Back 22

A defective RNA virus dependent on HBV for replication and its protective envelope.

Front 23

Who is at greatest risk for chronic carriage of HBV?

Back 23

Individuals infected as infants
90% of infected infants will progress to chronic HBV infection if not treated with vaccine and hepatitis B immune globulin.

Front 24

Is there a vaccine for HBV?

Who is it administered to?

Back 24

YES; a recombinant HBsAg
Routinely given in three doses to all children and those at high risk for exposure (health care workers)

Front 25

What type of nucleic acid do Herpesviridae contain in their genome?

What is their capsid geometry?

Do they contain an envelope?

Back 25

Linear dsDNA

Icosahedral

Yes, they are enveloped viruses

Front 26

What unique structure lies between the envelope and capsid in Herpesviridae?

Back 26

The tegument

Front 27

What is the tegument?

Back 27

A proteinaceous material containing virus-encoded enzyme and transcription factors.

Front 28

How does the tegument contribute to the pathogenicity of the virus?

Back 28

One of the tegument proteins is involved in activation of immediate early HSV-1 gene expression.

Front 29

Where does replication of a herpesvirus occur?

Back 29

In the nucleus

Front 30

What are the three phases of herpesvirus gene expression?

Back 30

1) Immediate-early
2) Early
3) Late

Front 31

What do immediate-early genes code for?

Back 31

Initiation of gene transcription in addition to a variety of regulatory functions.

Front 32

What do early genes code for?

Back 32

Enzymes that are necessary for replication of viral DNA including DNA polymerase, helicase, and thymidine kinase.

Front 33

Why do herpesviruses require production of viral DNA polymerase?

Back 33

They often infect nonreplicating cells (G0), i.e., cells that do not contain the cecessary enzymes for replication, e.g., neuronal cells.

Front 34

What do late genes code for?

Back 34

Structural proteins and proteins involved in assembly and maturation of viral progeny

Front 35

Where do Herpesviridae assemble?

Back 35

In the nucleus

Front 36

How do Herpesviridae acquire their envelope?

Back 36

Part of the envelope is acquired from the nuclear membrane, which is unlike most enveloped viruses that acquire their envelope form the plasma membrane.

Front 37

What concept is a major characteristic of herpesviridae?

What is this?

Back 37

Latent viral infections

A persistent infection with replication-competent virus that does not produce viral progeny.

Front 38

What are the three classes of the herpesvirus family?

How are these classes differentiated?

Back 38

1) Alphaherpesvirinae
2) Betaherpesvirinae
3) Gammaherpesvirinae

By their biologic characteristics, not by their morphology

Front 39

What are three clinically relevant Alphaherpesviruses?

Back 39

HSV-1
HSV-2
VZV

Front 40

Where do Alphaherpesviruses establish latency?

Back 40

Nerve ganglia

Front 41

What are three clinically relevant Betaherpes viruses?

Back 41

CMV
HHV-6
HHV-7

Front 42

What are the characteristics of the growth cycle of Betaherpesviruses?

Back 42

A slow repliction cycle resulting in formation of multinucleated, giant host cells.

Front 43

Where do Betaherpesviruses establish latency?

Back 43

Nonneural tissues, mainly macrophages and glandular tissue.

Front 44

What are two clinically relevant Gammaherpesviruses?

Back 44

EBV
HHV-8 (Kaposi sarcoma-associated herpesvirus)

Front 45

Where do Gammagerpes viruses establish latency?

Back 45

Mucosal epithelium, where they also induce proliferation of lymphoblastoid cells.

Front 46

What type of nucleic acid do Poxviridae contain in their genome?

What is their capsid geometry?

Do they contain an envelope?

Back 46

Linear, dsDNA with a large coding capacity.

Complex; it is neither icosahedral nor helical

YES, they contain a double envelope

Front 47

Where does replication of poxviruses occur?

How is it able to do this?

Back 47

Cytoplasm
Poxviridae are the only DNA viruses that replicate eentirely in the cytoplasm.

the virus encodes all enzymes necessary for replication, including a DNA-dependent RNA polymerase

Front 48

How large are the poxviruses?

Back 48

They are the largest viruses in size and are visible under the light microscope.

Front 49

What are three clinically relevant viruses of the Poxviridaa family?

Back 49

Variola
Vaccinia
Molluscum contagiosum

Front 50

What disease is caused by variola infection?

Back 50

Smallpox

Front 51

How does smallpox present clinically?

Back 51

Sudden onset of fever and malaise, followed by papular rash beginning on face and spreading to the extremities.

Front 52

What is the vaccine for smallpox?

Back 52

Live-attenuated vaccinia virus.

Front 53

How effective is the vaccine for smallpox?

Back 53

It was so effective that smallpox was the first infectious disease to be declared eradicated worldwide.

Front 54

What makes the smallpox vaccine so effective?

Back 54

1) Smallpox has only one stable serotype
2) There is no animal reservoir
3) the antibody response is prompt, so eposed people are protected
4) Subclinical disease is very rare; therefore most people infected with the virus are easily identified.
5) There is no carrier state.

Front 55

What disease is caused to vaccinia?

Back 55

Cowpox or 'milkmaid's blisters'

Front 56

How does molluscum contagiosum present clinically?

Back 56

Small, pink, wart-like benign tumor of skin or mucous membranes.