Lymphotropic Herpesviruses

Question 1

Lytic:

Latent:

Answer 1

Lytic: virus production and cell lysis

Latent: Viral genome silent in cells

Question 2

Replication and Latency

Cytomegalovirus:

Epstein-Barr virus and Kaposi’s sarcoma virus:

Roseolovirus:

Answer 2

Cytomegalovirus: Macrophage

Epstein-Barr virus and Kaposi’s sarcoma virus: Plasma cell

Roseolovirus: T-lymphocyte

Question 3

Cytomegalovirus

• Rate of seropositivity associated with _______ _____ and ____
• Infected cells identified by:

Answer 3

• Socio-economic condition; age
• Owl eye; inclusion body

Question 4

Cytomegalovirus disease

Answer 4

• Asymptomatic in healthy adults
• Leading cause of congenital birth defects
• Symptomatic upon immunosuppression
• Long term persistent infection associations
  
  • atherosclerosis
  • Immunosenescence
  • Neuroblastoma

Question 5

TORCH

Answer 5

Congenital birth defects: TOxoplasmosis, Rubella, Cytomegalovirus, Herpes simplex

Question 6

Basic characteristics of CMV

Answer 6

• 230 kbp double stranded DNA genome
  
  • Expresses >750 different proteins
  • Encodes its own DNA replication machinery
• Icosahedral nucleocapsid
• Tegument proteins and RNA
• Envelope with glycoproteins

Question 7

CMV lytic replication cycle

Answer 7

1. Binding/penetration
2. Entry
3. Transcription
4. DNA replication (24-48 hours)
5. Encapsidation (48-72 hours)
6. Envelopment/Release (72-96 hours)

Question 8

Stages of gene expression

Answer 8

Immediate, early, late

Question 9

What is the assembly compartment?

Answer 9

Proteins released from the nucleus into a compartment in the cytoplasm where virion assembly occurs

Question 10

Cytomegalovirus Transmission

Answer 10

• Direct contact with virus-containing secretions
  
  • bodily liquids
• Inoculation onto a mucosal site
• Other routes
  
  • blood transfusion
  • organ transplants
  • transplacental transmission
• Shedding with or without symptoms

Question 11

Transmission most often occurs at _________

Answer 11

daycares

Question 12

CMV dissemination

Answer 12

• Cell associated
• Slow replication cycle
• Lytic replication
  
  • epithelial, dendritic, fibroblasts, smooth muscle…
• Latent infection
  
  • CD34+ hematopoietic progenitor cells, monocytes

Question 13

Frequency of CMV reactivation

Answer 13

1 in 10,000 of infected monocytes

Question 14

Immune responses to CMV

Innate response:

Humoral response:

Cell-mediated immune response:

Answer 14

Innate response: Macrophage, interferon and NK cells control but are insufficient to clear

Humoral response: Does not clear, but may limit reinfection or reactivation

Cell-mediated immune response: Important cytotoxic T cells kill CMV infected cells up to 10% of all CD* T cells in the body may be directed against CMV

Question 15

Common CMV viral antigens

Answer 15

gB, gH, pp65, pUL128-31

Question 16

CMV symptoms in healthy adults and children

Answer 16

• Usually mild disease but often unapparent
• Fever, fatigue, sore throat, headache
• Liver function abnormalities
• Lymphocytosis
• Lymphadenopathy
• Mononucleosis

Question 17

Diagnosis of CMV

Answer 17

• Serology
• Owl’s eye cells in urine or other tissues
• Culture virus from clinical material and detect with immunofluorescence
• Detection of viral DNA using PCR/NAT

Question 18

Serology of CMV

Answer 18

• IgM testing is highly variable
• IgG indicates recent or distant past infection
• Serial testing of IgG negative to positive can define positive infection
• IgG avidity increases with time and can distinguish between recent and past infection

Question 19

Treatment of CMV infection

Answer 19

• Ganciclovir - inhibits viral DNA polymerase
• Foscarnet - Inhibits the pyrophosphate binding site on viral DNA polymerase
• Cidofovir - Inhibit viral DNA polymerase
• CMV does NOT encode thymidine kinase so Acyclovir is less effective

Question 20

Congenital CMV

Answer 20

• Only 14% of women have heard of CMV
• Perinatal infections
  
  • infection at birth from cervical/vaginal secretions
  • Transmission via mother’s milk
  • Usually no clinical signs

Question 21

Symptoms of infection

At birth:

Permanent symptoms:

Answer 21

At birth:

• Petechial lesions
• Small size
• Hepatosplenomegaly
• Jaundice

Permanent symptoms:

• Hearing loss
• Vision loss
• Mild to severe mental retardation

Question 22

Diagnosis of Congenital CMV infection

Answer 22

• Screening pregnant women for CMV remains controversial
• Detection of virus in amniotic fluid is a definitive test
• Newborns who are symptomatic are candidates for ganciclovir treatment

Question 23

CMV infection in immunosuppressed

Answer 23

• Life threatening
• Transplant patients
• HIV patients (Retinitis)
• Monitored by PCR/NAT or IgG and managed with antivirals

Question 24

ß-Herpes virus: HHV-6B

Disease in children:

Replication

Detection:

Answer 24

Disease in children:

• 90% of children > 2 years old are seropositive
• High fever
• Rash occurs in 10%

Replication: Replicates in CD4+ T cells

Detection: Using PCR/NAT or serology

Question 25

Epstein-Barr Virus (HHV4) ## Footnote Seropositivity: Disease:

Answer 25

Seropositivity: \>95% by early 20s worldwide - Asymptomatic infection Disease: * Infectious mononucleosis * Post Transplant Lymphoproliferative Disorder (PTLD) * Lymphomas (B, T and NK-cell)

Question 26

Basic characteristics of EBV

Answer 26

* 172 kbp dsDNA genome * Nucleocapsid, tegument, and envelop with glycoproteins * Encodes about 70 proteins including DNA replication machinery * Immediate, early , and late gene expression

Question 27

Possible outcomes of EBV infection

Answer 27

* Replicate in b cells or epithelial cells * Latent infection in memory B cells * Stimulate and immortalize B cells

Question 28

EBV lytic replication cycle

Answer 28

* Transmission by saliva and blood * Limited to epithelium of pharynx and B cells due to restricted cellular receptor expression * Reactivation of latently-infected activated B cells

Question 29

EBV ## Footnote Latency type I/II: Latency III:

Answer 29

Latency type I/II: * Viral antigens in memory B cells * EBNA1 (Latency I and II) * LMP1 and LMP2A (Latency II) * RNA EBER 1&2 * Can lead to Burkitt's, Hodgin lymphomas, nasopharyngeal carcinoma Latency III: * Viral antigens made in proliferating B cells * EBNA 1, 2, 3A, 3B, 3C, LP * LMP 1, 2A, 2B * RNA EBER1&2 * Infectious mononucleosis, PTLD

Question 30

Immune Response to EBV ## Footnote Humoral Response: Cell Mediated: Disease:

Answer 30

Humoral Response: * Neutralizing antibody - no effect on virus shed Cell Mediated: * CD8+ T lymphocytes and NK clls - lysis of EBV infected cells * Loss of T cell function results in B cell proliferative disease * Mononucleosis from rapid proliferation of atypical T cells (**Downey cells)** Disease: Overactive immune response

Question 31

EBV mediated infectious mononucleosis ## Footnote Epidemiology:

Answer 31

* Usually age puberty - 25 years * Primarily exposure to EBV * 30-40% develop disease/symptoms * Transmission by saliva * 5-20% of B cells infected with EBV in first week

Question 32

Post Transplant Lymphoproliferative Disease (PTLD)

Answer 32

* Immunosupressie therapy activated infection * Incidence 1-33% transplants depending on organ * Arises in donor B cells or reactivation in recipient * Prognosis is often poor 40-70% mortality

Question 33

Diagnosis of EBV

Answer 33

* Serology - assess antibody status against EBV antigens * EBV mononucleosis - test for heterophile antibodies by agglutination of animal red blood cells * Paul Bunnell test - sheep rbc * Monospot test - horse rbc * PTLD - fluorescent in situe hybridization; PCR

Question 34

EBV-Associated Lymphoma

Answer 34

* Burkitts lymphoma * Nasopharyngeal epithelial carcinoma * B cell lymphomas * Hodgkin and non-Hodgkin lymphomas * Immunosuppressed patients and transplant patients

Question 35

Kaposi's Sarcoma Herpesvirus (HHV8)

Answer 35

* 165 kbp dsDNA genome * 0-5% prevalent in North America and \>50% in parts of Africa * Seropositiveity varies with geographic area and correlates with incidence of KS