Human Herpes Viruses Flashcards
What kind of Genomic material is associated with the herpes viruses?
Large double stranded DNA genome.
How many herpes viruses are there that infect humans? Name them.
Herpes simplex virus 1 and 2 Varicella-zoster virus Cytomegalovirus Epstein-Barr virus Human herpes virus 6 and 7 and 8
Structure of a herpes virus particle?
Lipid belayer envelope
Tegument- amorphous layer of proteins
Icosahedral nucleocapsid
What is a characteristic of all herpes viruses?
Following primary infection > latent infection > virus may reactivate at any stage.
*reactivation associated with further disease normally
What kind of lesions do herpes simplex viruses 1 and 2 cause?
Painful vesicles on the skin at site of inoculation.
What is a vesicle?
Small, circumscribed elevation of the epidermis containing serous fluid.
What is HSV1 associated with?
Oro-facial lesions?
What is HSV2 associated with?
Genital lesions.
What two clinical patterns of disease do HSV show?
Primary infection
Reactivation
Characteristics of a primary infection?
Most are asymptomatic.
Or may present with a painful blistering rash.
How long does said painful blistering rash take to develop?
1-3 days post-exposure.
Characteristic of said vesicles?
They can spread to other areas of the skin and mucous membranes via auto-inoculation.
What are symptoms due to primary infection determined by?
The site of inoculation.
What five clinical presentations are associated with primary infection with herpes simplex virus?
Gingivo-stomatitis Eczema herpeticum Herpetic whitlow Conjunctivitis + keratitis Genital herpes
What is an ulcer?
A local defect or excavation of the surface of an organ or tissue produced by slouching off of necrotic inflammatory tissue.
Signs of Gingivo-stomatitis?
Vesicles inside mouth on the bucchal mucosa and gums as well as the lips and skin around the mouth.
- vesicles inside mouth ulcerated and become covered with grayish slough.
- lesions may be on head and neck.
Symptoms of Gingivo-stomatitis?
Fever
Cervical lymphadenopathy
How does one normally get Gingivo-stomatitis?
Kissing
How long do the vesicles of Gingivo-stomatitis take to heal?
Within 14 days.
*illness is self-limiting
What is eczema herpeticum?
Superinfection of eczema tours skin with HSV.
What is herpetic whitlow?
Inoculation of virus into the fingers.
*hazard of doctors, nurses and dentists
How do HSV affect the eyes?
Conjunctivitis. Also edema of lids.
Keratitis.
What is keratitis?
Inflammation of the cornea.
What is a herpetic lesion of the cornea called?
Dendritic ulcer.
*has a branching appearance.
How long do eye lesions due to HSV (conjunctivitis and keratitis) normally take to heal?
Lesions usually heal within 3 weeks.
What are features of a dendritic ulcer?
Pain
Photophobia
Which HSV virus is genital herpes due to?
Mainly HSV2 but 20-30% of cases are due to HSV1.
Features of genital herpes?
Vesicles in genital or peri-anal area.
*infection may be confined to the cervix in females
How long do the vesicles in genital herpes last?
14-21 days.
What is genital herpes associated with?
Aseptic meningitis.
What flows primary infection?
Latency.
Where does the virus go during latency?
Virus enters sensory nerve endings at the site of inoculation > travels up axon > latent infection in ganglion supplying that area of skin.
What is a ganglion?
Is a nerve cell cluster or a group of nerve cell bodies located in the peripheral nervous system.
Which ganglion/ganglia are involved in latent infection?
Genital area - sacral ganglia
Oro-facial area - trigeminal ganglion
How does the virus persist in the neuron?
In an episcopal (plasmid) form in the NUCLEUS of the neuron.
How does reactivation occur?
Virus travels down the axon > re-infect skin/mucous membrane in area supplied by that nerve.
Stimuli that may provoke reactivation?
Sunlight Stress Febrile illnesses Menstruation Immunosuppression
What are the clinical manifestations associated with reactivation?
Cold sores
Recurrent genital herpes
Aseptic meningitis
Keratitis
How do cold sores differ to Gingivo-stomatitis?
Lesions more localized.
Lesions heal faster. (7-10 days)
What often precedes eruption of cold sores?
Parasthesia.
How does recurrent genital herpes differ from primary infection of genital herpes?
Lesions less extensive.
Lesions heal faster.
*recurrence more common with HSV2
What syndrome is HSV2 rarely associated with upon reactivation?
Mollarets syndrome:
Aseptic meningitis associated with HSV2 reactivation.
Reactivation in cornea of eye via which nerve?
Ophthalmic branch of the trigeminal nerve.
How does recurrent keratitis differ to primary infection keratitis?
Dendritic ulcer heals faster.
Name three life-threatening syndromes caused by HSV.
Acute necrotizing encephalitis.
Neonatal infection.
Disseminated HSV infection in adults.
What is acute necrotizing encephalitis?
Infection of the brain by HSV.
What part of the brain is involved in acute necrotising encephalitis and what happens to it?
Temporal lobe.
Necrosis of said tissue.
Clinical features of acute necrotising encephalitis?
Fever.
Headache.
Confusion.
Alteration in personality.
At which stage of HSV infection can acute necrotising encephalitis occur?
Primary infection or following reactivation of latent virus.
Prognosis of acute necrotising encephalitis?
Mortality is high.
Neurological impairment in survivors is invariable.
Why is neonatal infection with HSV such a serious condition?
Neonate shave poor cell-mediated immunity and are therefore at more risk of disseminated infection.
How can neonate acquire a neonatal infection?
If they are exposed to HSV in the peri-natal period.
*is a rare condition
How may a baby be exposed to HSV?
During birth - only risk if primary infection.
If the baby is handled by people with herpetic lesions.
What three forms may neonatal infection take?
Cutaneous.
Generalized infection.
Encephalitis.
Features of cutaneous neonatal infection?
Lesions are confined to skin. GOOD PROGNOSIS
What happens in generalized infection in neonatal infection?
Virus disseminates throughout organs. POOR PROGNOSIS.
Clinical features of generalized infection in a neonate?
Jaundice. Hepatosplenomegaly. Thrombocytopenia. Pneumonia. Encephalitis.
What is encephalitis regarding to a neonatal infection?
Infection of brain tissue by HSV.
POOR PROGNOSIS.
Features of disseminated HSV infection in adults?
Sometimes occurs in apparently health adults.
Disease follows fulminant course > patients die before diagnosis is made.
Clinical manifestations of disseminated HSV infection in adults?
Fulminant hepatitis.
Pneumonitis.
Multi-organ failure.
Encephalitis.
Ways to detect HSV in the lab?
Direct detection:
- Electron microscopy/immunoflourescence
Cell culture:
- monitor for development of characteristic cytoplasmic effect
Serology:
- IgG = immunity (past exposure)
- IgM = marker of primary or recurrent infection (not reliable)
PCR:
- PCR of CSF best for detecting HSV encephalitis
Drug of choice for treating HSV infections?
Acyclovir
What is acyclovir?
A nucleoside analogue of guanosine.
*acts like nucleoside guanosine during DNA synthesis
Drug activity?
Active against replicating virus but not latent virus.
What formulations of acyclovir are available?
Oral.
Topical.
IV formulations.
