12. Latent Viral Infections: Herpes Viruses - Audia

Herpes Virus

Characteristics (9)

1. Large dsDNA genome

2. Common structure (enveloped virus)

3. Infections are often asymptomatic

4. Establish latency - persist for life

5. Can reactivate from latency

6. Most reactivations are asymptomatic

7. Re-infections can occur

8. Most herpesviruses cause more than 1 disease

9. Interfere with immune response

Human Herpes Viruses

Genome Characteristics (3)

1. DNA Viruses

2. Double-stranded

3. Enveloped

What are the 3 Classes of Herpesviruses?

• examples of each (3, 3, 2)

Alpha:

• Herpes Simplex I (HSV-1)

• Herpes Simplex II (HSV-2)

• Varicella-zoster virus (VZV)

Beta:

• Cytomegalovirus (CMV)

• Herpesvirus 6

• Herpesvirus 7

Gamma:

• Epstein-Barr (EBV)

• Herpesvirus 8

Summary of Diseases

List diseases caused by the following Herpesviruses:

• HSV-1 (3)

• HSV-2 (3)

• VZV (2)

HSV-1:

• Keratoconjuctivitis

• Gingivostomatitis

• Encephalitis

HSV-2:

• Genital Herpes

• Neonatal herpes

• Meningoencephalitis

VZV:

• Chickenpox

• Shingles

Summary of Diseases

List diseases caused by the following Herpesviruses:

• EBV (3)

• CMV (4)

EBV:

• Infectious mononucleosis

• Burkitt’s lymphoma

• Nasopharyngeal cancer

CMV:

• Cytomegalic inclusion disease

• CMV mononucleosis

• Pneumonia

• Retinitis

Summary of Diseases

List diseases caused by the following Herpesviruses:

• HHV-6

• HHV-7

• HHV-8

HHV-6:

• Roseola

HHV-7:

• Roseola

HHV-8:

• Kaposi’s lymphoma

Overview of HSV Replication (8)

• Replication occurs where?

1. Binding (attachment)

2. Direct Fusion (entry)

3. mRNA synthesis

4. Protein Synthesis

5. DNA Replication

6. Glycoprotein Synthesis

7. Assembly

8. Release

Replication occurs in NUCLEUS

Important HSV Enzymes (3)

• what can be targeted*

1. DNA-dependent DNA polymerase

2. Thymidine kinase

3. Ribonucleotide reductase

Draw out Replication of Herpes Simplex Virus

Stage I

• what is released? (2)

Alpha proteins (transcription regulation)

Beta proteins (DNA polymerase)

What genes/transcripts are turned on? (2)

• in what order?

• function of each

1. Alpha proteins: immediate-early

   • Transcription regulation

2. Beta proteins: early

   • DNA polymerase

Draw out Replication of Herpes Simplex Virus

Stage II

Draw out Replication of Herpes Simplex Virus

Stage III

Assembly occurs where?

Nucleus! (buds from the nuclear membrane)

What are produced in Sensory Neurons?

• What do they do? (2)

microRNA precursors called Latency-associated transcripts (LATs)

• bind early transcripts and prevent/SILENCE their expression (early genes - alpha proteins, needed for viral replication)

  • prevents viral replication

Reactivation of Herpes Simplex Virus

• What can reactivate? (2, etc)

• What happens after? (3)

Stimuli:

• stress

• UV light, etc

Reactivation:

1. Viral replication

2. Transport along periphery sensory nerves

3. Replication in the epithelium with the production of vesicles

HSV uses what type of transport?

Retrograde transport

• ex.) lips to the nucleus and anterograde transport back to the site of infection.

Pathogenesis of Herpes Simplex Virus

General (2)

HSV-1

HSV-2

Immunocompromised → Dissemination

Diagnosis of HSV Infections (3)

• Examples of each (1)

Virus Isolation:

• Cytopathic Effect

Direct analysis of clinical sample:

• Tznack Smear - a scraping of the base of a lesion

  • Cowdry Type A nuclear inclusions

Immunofluorescence Staining

Epstein-Barr Virus

Epstein-Barr Virus

• Causative agent of what?

• Causally associated with what? (3)

• Causative agent of Infectious Mononucleosis

• Causally associated with:

  • Burkitt's Lymphoma

  • Hodgkin's Lymphoma

  • Nasopharyngeal Carcinoma

Epstein-Barr Virus

• Replicates in what cells? (2)

• Causes latent infection in what cells?

  • What else does it cause in these cells? (2)

• Replicates in B-cells or permissive epithelial cells

• Causes latent infection of B-cells

  • Stimulates and Immortalizes B-cells

What are the 2 EB nuclear antigens involved?

When does EBV become activated?

When infected B-cells undergo Lytic Replication

What allows EBV to enter Latency and evade host immune system?

Establishes Latency in what types of cells?

EB nuclear antigens:

• EBNA-1

• LMP-2a

Establishes in Memory B-cells

Overview of Epstein-Barr Virus (6)

1. Virus in saliva infects oral epithelial and B cells in lymphatic tissue where it initiates productive infection

2. Virus immortalizes B cells (proliferation)

3. T-cells kill and limit B cell outgrowth

4. Virus establishes Latency in memory B cells

5. T-cell response (lymphocytosis) contributes to symptoms of mononucleosis

6. Can be responsible for lymphoma in immunosuppressed persons and African children in malarial regions (African Burkitt’s lymphoma) and with nasopharyngeal carcinoma in China

EBV Antigens on the following:

• Burkitt’s Lymphoma (1)

• Hodgkin Lymphomas (2)

• Nasopharyngeal Cancer (2)

Burkitt’s Lymphoma:

• a B-cell tumor of face and jaw expressing EBNA-1

Hodgkin Lymphomas:

• many of these tumors express EBNA-1 and LMP-1

Nasopharyngeal Cancer:

• a tumor of epithelial cell origin expressing EBNA-1 and LMP-1

Epstein-Barr Virus

Pathogenesis (Picture)

⭐What should point you to EPV or Cytomegalovirus? (4)

1. Pharyngitis

2. Swelling of lymph nodes

3. Atypical lymphocytes (downey cells)

4. Heterophile antibody (+ in EBV, - in CMV)

Pathogenesis of EBV

Steps (3)

• 6, 1, 2

1. Infection:

   1. Saliva with EBV → Epithelial cells or B Lymphocytes in submucosa

   2. Transformed B cell

   3. EBV antigens expressed

   4. B-cell proliferation = mononucleosis

   5. Seeds lymphoid organs

   6. Lymph node, spleen, bone marrow

2. Immune Response:

   1. EBV-specific CD4, CD8, and B cells stimulated

3. Recovery:

   1. Cell-mediated and humoral immunity induced

   2. Oropharyngeal and replication suppressed

Epstein Barr Diagnosis (4)

• Symptoms (6)

• Complete Blood Cell Count (2)

Symptoms:

• mild headache, fatigue, fever

• Triad:

  • Lymphodenopathy

  • Splenomegaly

  • Exudative Pharyngitis

• Other:

  • hepatitis

  • ampicillin-induced rash

Complete Blood Cell Count:

• hyperplasia

• atypical lympocytes (downey cells)

Heterophile Antibody (transient)

EBV-antigen specific antibody

Epstein-Barr Virus

Effective Treatment/Vaccine

NO effective treatment or vaccine!

• best to be infected early in life — more benign

What are these? What virus?

Atypical T-cells (Downey Cells)

Epstein Barr Virus

Epstein-Barr Virus

When do antibodies (IgG) begin to appear?

months after clinical syndromes

IgM antibodies appear 10 days after clinical syndromes

Cytomegalovirus (CMV)

• The most common viral cause of what?

• Important as a ____ pathogen in immunocompromised patients

• Many cell types are ____

  • examples (3)

• Virus can establish latency in what? (2)

Most common viral cause of congenital defects

Important as a opportunistic pathogen in immunocompromised patients

Many cell types are permissive

• fibroblasts

• epithelial cells

• macrophages and others cells

The virus can establish latency in:

• mononuclear lymphocytes

• stromal cells of the bone marrow and others cells

Cytomegalovirus (CMV)

• What class of Herpesvirus?

Beta class

Epstein-Barr Virus (EBV)

• What class of Herpesvirus?

Gamma class

Cytomegalovirus (CMV)

• Transmission through what? (8)

• Significant fact about transmission

1. Oropharyngeal Secretions

2. Cervical and Vaginal Secretions

3. Spermatic Fluids

4. Urine

5. Breast Milk

6. Tears

7. Blood

8. Feces

Can be transmitted through PLACENTA to baby!

BODILY FLUIDS

Cytomegalovirus (CMV)

• Possible Pathways (3)

⭐Which Herpesvirus is Heterophile Ab negative? Which is not?

Heterophile Ab (+) → Epstein-Barr Virus

Heterophile Ab (-) → Cytomegalovirus

Cytomegalovirus (CMV)

Pathogenesis (draw out)

Cytomegalovirus (CMV)

• Immunity is mediated by what cells?

• What helps in clearing active infection and maintaining the virus in its latent state? (2)

  • What can cause reactivation?

• Immunity is mediated by T-cells

• NK cells and antibody participate in clearing active infection and in maintaining virus in latent state

• Impairment of immunity can result in reactivation

Cytomegalovirus (CMV)

• Histological hallmark?

• Diagnosis how? (3)

Histological Hallmark:

• cytomegalic cell - enlarged cell that contains a dense, central “owls eye” intranuclear inclusion body

Diagnostics:

• Antigen detection using immunofluorescence

• ELISA

• PCR

Treatment of Herpes Virus Infections

• Treatments (4, 3+2+1+1)

• What do they all have in common?

• Which drugs are readily absorbed from the gut?

  • What does this do?

1. Acyclovir: analog of Guanosine

   • phosphorylated by viral thymidine kinase, then further by cellular enzymes to be ACTIVATED

   • activated only in infected cells

   • Terminates synthesis because Acyclovir lacks 3’—hydroxyl group (Chain terminator)

2. Penciclovir: analog of Acyclovir

   1. phosphorylated more efficiently

   2. intracellular half-life is 10-fold longer but 100x less potent in its inhibition of viral DNA polymerase

3. Valaciclovir: Acyclovir analog

4. Famciclovir: Penciclovir analog

All use NUCLEOSIDE ANALOGS to mess up viral replication

Valaciclovir/Famciclovir are more readily absorbed from the gut → increases plasma levels over the parent compound

Herpes Virus Infections

What can treat latent infections?

Treatments for HSV-1 and HSV-2 (2)

• Characteristics of each (4, 1)

NOTHING

Ara-A (Adenine Arabinoside) (Vidarabine):

• Analog of Adenosine

• Phosphorylated by cellular kinases to triphosphate

• Competitive inhibitor of HSV DNA polymerase

• Disadvantages:

  • high toxicity

  • low solubility

Trifluorothymidine (TFT):

• incorporates causing errors

Clinical Uses

• Oral Acyclovir, Valacyclovir, and Famciclovir are effective treatments for what? (3)

• IV Acyclovir can be used to treat what?

• For genital HSV infections, when is treatment beneficial?

• Oral Acyclovir, Valacyclovir, and Famciclovir are effective treatments for:

  • oral mucosal lesions

  • genital lesions

  • keratitis

• IV Acyclovir can be used to treat HSV-1 encephalitis

• For genital HSV infections, treatment is beneficial in first outbreak if given early

  • treat themselves at first “tingle” of a new outbreak

Clinical Uses

• Oral Valacyclovir can be given to people when? Why?

• What OTC cream can be used?

  • What is it?

  • What does it inhibit?

• Oral Valacyclovir can be given to people when they have frequent genetical occurrences for 1 year or longer

• Docosanol (Abreva)

  • OTC cream

  • active ingredient is a 22 carbon alcohol

  • inhibits viral attachment

  • reduces symptoms when applied early (prodrome)

Cyclomegalovirus

Treatment

• structure?

• lacks what?

• characteristics (3)

Significant FACT

Ganciclovir:

• chemically slightly different from Acyclovir (additional hydroxymethyl group)

• lacks the thymidine kinase of other herpes viruses

• Characteristics:

  • CMV encodes a different kinase to phosphorylate Ganciclovir

  • Cellular enzymes convert Ganciclovir monophosphate to triphosphate

  • Triphosphate form of Ganciclovir inhibits CMV DNA polymerase more efficiently than it inhibits host cell DNA polymerase

ACYCLOVIR and analogues are NOT effective b/c CMV lacks TK gene!

Resistance to 2nd generation antivirals can occur by what 2 mechanisms?

Which is the most common resistance mechanism?

1. Thymidine kinase (or CMV viral kinase) undergoes mutation so that it no longer phosphorylates the drug

   • this is the most common resistance mechanism

2. DNA polymerase gene undergoes mutation so that they polymerase no longer recognizes the phosphorylated analogs

What drugs are useful in treating:

• Acyclovir-resistant HSV (2)

• Ganciclovir-resistant CMV (1 + 3)

Acyclovir-resistant HSV:

1. Adenine arabinoside (Ara-A)

2. Foscarnet

   1. binds directly to HSV DNA polymerase and inhibits its action

Ganciclovir-resistant CMV: Cidoforver

• drug not dependent on CMV kinase for its activity

• posses initial phosphate: cytidine analog

• inhibits CMV DNA polymerase directly

What can be taken when patient experiences tingling sensation?
What does this sensation indicate?

Acyclovir

• tingling sensation is a prodromal symptom that indicates the onset of a herpes virus outbreak

• Taking Acyclovir at this stage can help reduce the severity and duration of the outbreak