Herpesviruses

Question 1

Herpesviruses

Answer 1

Double-stranded DNA genome
A capsid surrounded by a tegument and an envelope.

Herpes simplex virus 1 (HSV-1)
Herpes simplex virus 2 (HSV-2)
Cause oral and genital herpes

Human cytomegalovirus (HCMV)

Varicella-zoster virus (VZV)
Causes chickenpox and shingles.

Epstein Barr virus (EBV)

Human herpesvirus 6A/6B (HHV-6A/6B)
Human herpesvirus 7 (HHV-7)
Kaposi’s sarcoma-associated
herpesvirus (KSHV/HHV-8)

Question 2

Herpesvirus lytic cycle.

Answer 2

Lytic cycle

Entry
Glycoproteins essential for binding and fusion.
1.Binding and fusion at cell membrane.
2.Viral envelope interact directly with plasma membrane and fuse with cell surface or endocytosis
3. Capsid with DNA released into cytoplasm of cells.
4. DNA virus is replicated in nucleus so capsid is transported through nuclear pore into the nucleus.

Expression of immediate early
genes (IE)
Transactivate viral
“early” gene expression (E)

Expression of
Early genes (E)
Establishment of viral DNA
replication

Expression of
Late viral genes

Structural proteins:
Capsid
Tegument
Glycoproteins

Assembly and Egress: New viruses are assembled in the nucleus, acquire an envelope, and are released via exocytosis or cell lysis.

Question 3

Herpesvirus Disease Associations
Latency

Answer 3

HSV-1/HSV-2: Cold sores, genital herpes (mucosa)
VZV: Chickenpox in children, shingles in adults.
HSV and VZV: Establish latency in sensory neurons

CMV: Severe systemic infections, retinitis.
CMV: Latent in monocytes and other cell types.

EBV: Infectious mononucleosis.
KSHV: Kaposi’s sarcoma, especially in HIV-positive individuals.
EBV and KSHV: Latent in B cells.

Question 4

Herpesvirus Latency
Reactivation:

Answer 4

Herpesviruses can establish latency, a state in which the virus remains dormant within the host cells without producing new virions.
Lytic gene expression is suppressed.

The viral genome persists intact so that productive infection can be initiated to ensure spread to new hosts.

Triggered by stress, immunosuppression, or other stimuli.
Leads to the reactivation of lytic replication and the recurrence of disease symptoms.