MICROBIOLOGY - Viral Infections Flashcards
What is the mechanism of action of aciclovir?
Inhibits DNA polymerase
What type of viruses are herpes virus?
double stranded DNA viruses
What are the main subtypes of herpes viruses?
alpha, beta, gamma
Alpha: HSV-1, HSV-2, VZV
what is the pathogenesis of herpetic disease?
Virus attaches to gD (host cell receptor) and through molecules such as nectin, herpes viral entry mediator and other glycoproteins, it facilitates viral capsid into the host cell, and fuses with host cell for endocytosis
Capsid is transported to nucleus using host cell DNA polymerase and virions are released from host cells to infect other nearby cells.
Virus replicates (via TLR-9) in epithelium and travels ciliary and ophthalmic nerves to the trigeminal ganglion via RETROGRADE TRNSPORT.
Has latency in the trigeminal ganglion, after reactivation, has ANTEROGRADE transport through neurons to original site of corneal infection
What is the structure of CMV?
Double stranded DNA virus
What is the pathogenesis of CMV? What is the histopathological sign?
Primary infection: CD8 T cell mediated and the virus becomes latent withn lymphocytes.
Owl’s eye inclusion bodies are specific histopathological sign.
Affects retina primarily at posterior pole
What virus is Kaposi’s sarcoma associated with?
- HHV-8
- HIV
What is the structure of adenoviruses? What are the serotypes?
double stranded DNA viruses.
3 and 7 serotypes - pharyngoconjunctival fever
8, 19, 35: keratoconjunctivitis
What are the virulence factors / pathogenesis of adenoviruses? (4)
- Disrupt MHC presentation by infected cells
- Suppress transcription encoding class I MHC
- Inhibition of cell lysis by TNF
- Interacts with retinoblastoma and p53 genes
Which virus causes corneal scarring with vitamin A deficiency?
Measles (parmyxovirus RNA)
What are the ocular manifestations of rubella? (8) are the non-ocular manifestations of rubella? (3)
What is its structure?
togavirus (single stranded RNA)
- Cataracts (pearly white)
- Microophthalmia
- Glaucoma
- Cloudy cornea (keratitis/raised IOP)
- Pigmentary retinopathy (most common - salt and pepper fundus)
- Fuch’s Heterochromic Uveitis (in adults)
- Keratoconus
- Strabismus
Non ocular: Cardiac abnormality, sensorineural deafness, encephalitis
What is the structure of HIV? What are the subtypes?
single stranded RNA virus containing reverse transcriptase (two copies)
Type 1: urban centres, homosexuals and IVDU
Type 2: African, heterosexual transmission
What is the pathogenesis of HIV infection?
- Binds to CD4 receptors on T-helper cells with CCR5 or CXCR4 as co-receptors
- gag gene encodes the core nucelocapsid polypeptides
- viral reverse transcriptase transcribes ssRNA to dsDNA - highly error prone so new strands made
- Complementary DNA becomes part of host genome (provirus)
- Multinucleate cells form after infection leading to cell death, destroying CD4 cells
- Decreased cell mediated immune response and decreased T cell dependent immunoglobulins.
What are the main changes seen in AIDS vs HIV? (3)
- Increase in p24 (core protein) and decrease in antibodies to core proteins - detects early HIV infection
- reduced CD4:CD8 ratio (<1)
- antibodies to gp41, gp120 and gp160 envelope glycoproteins - HIV produces different glycoprotein envelopes making it better at escaping host immunity.
What are the ocular manifestations of HIV?
- Extraocular movement complications
- Retinopathy (cotton wool spots, perivasculitis and retinal haemorrhages)
- Optic neuropathy
- Thin RNFL layer
- Mild colour vision loss, mild contrast sensitivity loss
- Mild visual field defects
What are the adenovirus serotypes that cause
1. epidemic keratoconjunctivitis
2. acute follicular conjunctivitis
3. acute haemorrhagic conjunctivitis
4. pharyngoconjunctival fever
- epidemic - 8, 9, 37
- acute follicular - 1, 2 ,3 ,4, 7, 10
- acute haemorrhagic - 11, 21
- pharynchoconjunctival - 3, 7
What is the most common neoplasia in HIV?
What is the most common CNS neoplasia in HIV/AIDS?
- kaposi sarcoma
- Non-Hodgkin B cell lymphoma
What are DNA viruses?
What are RNA viruses?
DNA: HECAP
HSV (double stranded) , EBV, CMV, Adenovirus, Pox (molluscum contagiosum)
RNA:TROP
Togavirus (rubella), Retrovirus (HIV), Orthovirus (Influenza), Paramyxovirus (Mumps, measles)
What are the structures of DNA viruses? What are the structures of RNA viruses? ie which ones are single stranded, double stranded enveloped or unenveloped
What are the ocular associations of rubella? What is its main differential
- Cataract
- Glaucoma
- Pigmentary retinopathy
- CLoudy COrnea (keratitis/raised IOP)
- Micro-ophthalmia
- Iris Dysplasia
- Fuch’s Heterochromic uveitis (in adults only)
Differential: Usher syndrome (deafness and pigmentary retinopathy
What are the ocular signs of subacute sclerosing panencephalitis? When do they occur? Whats its diagnosis?
Ocular manifestiations occur 2 years before neurological manifestations
Occurs as late complication of acquired measles infection
- Focal retinitis, RPE change
- Papilloedema, optic atrophy
- Minimal vitritis
Diagnosis: EEG abnormality, raised IgG in plasma/CSF
What is the main differential for congenital rubella?
Usher syndrome - both syndromes have deafness and pigmentary retinopathy
What are the most common ocular manifestations of congenital measles?
Profound vision loss 6-12 days after exanthem.
Findings: Retinal oedema, macular star, blurred discs. Later develop secondary pigmentary retinopathy (bony spicules)
What type of inclusions do RNA virus produce?
What type of inclusions do DNA virus produce?
RNA: cytoplasmic inclusions
DNA: intranuclear inclusions
What are the two vaccines offered against HZO/Shingles in UK?
- Zostavax - Live vaccine, one dose
- Shingrix - two doses
National program - 70-79 years old
What are the main causes of infectious scleritis? (5)
- Gram +ve cocci - staph/strep
- Mycobacteria
- HSV
- VZV
- Fungi
Which virus cause acute haemorrhage conjunctivitis (2)
- Picornavirus (Coxsackie A24 and enterovirus E70 - classic)
- Adenoviral
What is rubellas incubation period?
At what point is maximal infectivity for a rubella infection?
- Incubation period - 14-21 days
- 24 hours before patient develops a maculopapular rash.
HEP A
HEP B
HEP C
HEP E
Which substance can kill exogenous HIV?
strong acid and alikali or 10% bleach or 50% ethanol
Which HPV are associated with conjunctival carcinoma?
Which HPV are associated with conjunctival papilloma?
HPV carcinoma: 16 and18
HPV papilloma: 6 and 11
Which cellular infiltrate is implicated in herpes zoster ophthalmicus? Which nerve is it typically seen in?
Lymphocytic infiltrate appears around long and short ciliary nerves in HZO.
What type of cell is in a Kaposi sarcoma? Which layer does it involve?
Proliferation of spindle shaped cells and vessels in the dermis layer
Ring-Shaped corneal stromal infiltrate seen in herpes simplex keratitis is caused by?
Antigen-antibody complexes
What are the DNA viruses (7)
- Adenovirus
- Herpes SIMPLEX virus
- Varicella ZOSTER virus
- Epistein Barr virus
- Cytomegalovirus
- Molluscum contagiosum virus
- Vaccinia and variola virus
Whats the difference between ARN and PORN?
What is the difference between progressive outer retinal necrosis and ARN? (3)
- Usually impacts immunocompromised patients vs immunocompetent patients in ARN
- Typically minimal intraocular inflammation, AC and vitreous involvement in ARN, not in PORN.
- Large well-defined white retinal patches which can be peripheral or central
