Neurotropic Viruses

Question 1

What are unique characteristics of herpesviruses?

Answer 1

Contain Thymidine Kinase and viral DNA Polymerase
Synthesis of viral DNA and capsid occur in the CYTOPLASM
Lytic vs Latent lifestyle

Question 2

How does HSV become latent in the host cell?

Answer 2

Circular DNA enters the nucleus and associates with nucleosomes/chromatin and has very little expression of genes.

Question 3

What are common reasons for reactivation of latent HSV?

Answer 3

• immune system suppression
• UV radiation
• stress/trauma –> immune suppression

Question 4

What typs of HSV are located where in the body?

Answer 4

HSV-1 — oral cavity

HSV-2 – gential region

Question 5

How is HSV transferred to other individuals?

Answer 5

Usually direct contact with an infected region. Virus shedding occurs in saliva and from lesions in mouth and genitals.

Question 6

What are the steps in primary infections of HSV?

Answer 6

1. Virus invades mucous epithelial cell - lytic cycle, and virions released deeper and able to infect sensory neurons.
2. After invasion of neuron retrograde transport to nearest ganglion to set up latency.
   - -Most common are trigeminal and sacral ganglion

Question 7

What happens when HSV is reactivated?

Answer 7

From the ganglion the virus reactivates sending virions anterograde down the neuron back to the original location of inoculation site to produce mature virions/lesions on epithelial surface

Question 8

What is a rare occurance of reactivation of herpes virus in immunocompromised and elderly individuals?

Answer 8

There is RETROGRADE transport from ganglion deeper into the CNS causing Herpes Encephalitis.

Question 9

What is the key enzymes capitalized upon when treating HSV?

Answer 9

Thymidine Kinase only expressed in herpes infected cells, which activates the anti-virals with limited toxicity.

Question 10

What is the nucleoside analog that is the drug of choice of treatment of HSV?

Answer 10

Acyclovir - The phosphorylated version is recognized by viral DNA Polymerase, but not host, since viral is more nonselective.
–Causes chain elongation termination–

Question 11

What is primary HSV-1 infection called and expressed as?

Answer 11

Herpes Gingivostomatitis - lesions around the oral cavity and can occur in the oral pharynx as well.
Herpes Libialis - secondary/recurrent infection

Question 12

What is the most common cause of neonatal herpes and what are the symptoms?

Answer 12

Most common is inoculation by birth canal.
Neonate is immunocompromised, thus it becomes systemic expressing lesions everywhere and penetrates the CNS. High Mortality rate, if survival, then neurologic deficits.

Question 13

What is a leading cause of blindness in the US?

Answer 13

Keratitis and Conjunctivitis, HSV in the eye with recurrent infections.

Question 14

Where is the infection in Whitlow?

Answer 14

Hand dermatitis and fingers. Highly contagious.

Question 15

What is unique about Varicella-Zoster virus?

Answer 15

Becomes systemic after infection and is able to aerosol virions from the respiratory tract to infect others.

Question 16

Where does VZV replicate and become latent?

Answer 16

Replicates in T-cells and epithelial cells and becomes latent in sensory ganglia.

Question 17

How does latency compare in VZV to HSV?

Answer 17

VZV latency virus produces more viral products, but recurs less than HSV.

Question 18

What are the symptoms of VZV?

Answer 18

Cough
Fever
Lesions - primarily on the trunk
Malaise

Question 19

What is the difference between primary infections in children and adults?

Answer 19

Children = mostly skin lesions, minimal secondary infections
Adults = Can get more severe secondary infections including pneumonia and CNS invovlement

Question 20

What occurs with reactivation of of VZV?

Answer 20

Reactivation from a single ganglion and dermatome expressing surface lesions producing intense pain.

Question 21

What is Postherpetic neuralgia?

Answer 21

The pain associated with herpes-zoster that can be present even without lesions or before they arise.

Question 22

What is the benefit of receiving the VZV live attenuated vaccine?

Answer 22

Has a live version of VZV that still becomes latent, but is a weaker virus than wild strain. If you become infected by wild strain can still develop symptoms, but they will be lesser version.
–Can still develop Herpes-Zoster late in life when you received the vaccine

Question 23

What is the “Shingles” vaccine?

Answer 23

The Shingles vaccine is a larger dose of the VZV vaccine for children to ideally reduce the risk of developing shingles by increasing immune response to the virus. Age 60+