Viral Skin and Soft Tissue Infections Flashcards
What are the three subfamilies of Herpesviruses? How many are considered human herpesviruses?
- Alphaherpesviruses
- Betaherpesviruses
- Gammaherpesviruses
8 are considered human herpes viruses
What three viruses fall in the alpha herpesvirus family?
Herpes Simplex Virus 1 (HSV-1)
Herpes Simplex Virus 2 (HSV-2)
Varicella-Zoster Virus (VZV)
What is the B virus?
A monkey alpha herpesvirus which can infect humans only by bite, and can result in fatal encephalitis
What three viruses fall in the beta herpesvirus family?
Cytomegalovirus (CMV)
Human Herpesvirus 6A and 6B (HHV-6A, HHV-6B)
Human Herpesvirus 7 (HHV-7)
What two viruses fall in the gamma herpesvirus family?
Epstein-Barr Virus (EBV)
Human Herpesvirus 8 (HHV-8)
What causes herpes labialis, and what age group does it affect most?
HSV-1 more often than HSV-2, “cold sores”
Affects children and adolescents most
What causes genital herpes?
HSV-2 > HSV-1
What is another common HSV-1 complication?
Keratoconjunctivitis, which can cause blindness
What are some of the rarer HSV-1 complications?
dermatitis, encephalitis, disseminated HSV (in immunocompromised)
Who is most likely to be infected with a systemic HSV-2 infection which is very dangerous?
Neonates, general herpes and encephalitis can be very severe
What is the definition of HSV latency?
Continued presence of viral genome in lysogenic cycle, in the absence of viral replication / particles. Latency always happens and lasts a lifetime
How does HSV latency initially occur?
HSV enters into nerve cells, is transported to the relevant sensory ganglion, and viral replication occurs in the ganglion for several days before latency occurs
When does HSV reactivation occur? What initiates it and where does it occur?
Spontaneously, often induced by sunburn, stress, menstruation, or immunocompromisation
Activated by a neuron-specific JNK kinase pathway
Virus replicates and travels back down the axon to cause infection by the site of primary infection
What is the structure of HSV and its genome?
Large, enveloped DNA virus with icosahedral capsid
Linear, ds DNA genome with about 80 genes
What is the process of HSV attachment to integration into genome?
Virion attaches via heparan sulfate on cell surface, and is either endocytosed or directly fuses with virion envelope.
Capsid is transported to nuclear pore via microtubules, and released into the nucleus
What are the three phases of HSV gene expression?
- Immediate early genes adapt cell for virus replication
- Early genes produce / replicate viral DNA
- Late genes include structural proteins
Where is the viral DNA packaged into capsids and then ultimately released?
In the nucleus, packaged into capsids.
Naked capsid passes into cytoplasm via temporary envelop of nuclear membrane, then is finally enveloped via Golgi apparatus
What are two key HSV-coded enzymes?
- DNA Polymerase
2. Thymidine Kinase (TK)
What is the mechanism of acyclovir?
Nucleotide analog to thymidine.
Phosphorylated by HSV’s TK to acyclovir monophosphate, then made into triphosphate by cellular kinases.
This acyclovir-trisphosphate functions to:
- inhibit viral DNA polymerase
- terminate nascent viral DNA strands
What is valacyclovir? Does this work on latent virus?
The prodrug form of acyclovir with higher bioavailability
Neither this or acyclovir will work on latent virus
What are complications of varicella?
Pneumonia, inflammation of brain or spinal cord, congenital birth defects
Where does latent VZV stay?
Dorsal root ganglia