- Not by (direct / indirect) contact / droplet / airborne / fomites / environment - No natural (non-iatrogenic) person-person spread - Iatrogenic transmission (<1%) e.g. transplant, transfusion, medical equipment

L12 - Prion CNS infections and Antivirals Flashcards by Max Kam

Define Prion and its pathogenesis. What is it resistant to?

Infectious, misfolded “isoform” of a normal cell glycoprotein. No nucleic acid

Relatively resistant to heat (121oC, 15 min), UV light, ionizing radiation, formalin

Genetic or exogenous infection
» introduce Pathogenic prion
» prion turns normal proteins abnormal

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Difference between PrPc and PrPsc?

PrPc (c = cellular; normal) = protease-sensitive
PrPsc = Protease-insensitive: retains folding even in gastrointestinal tract

> > Catalyzes abnormal change in normal protein shape
PrPSc accumulates = disease

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Consequence of Prion accumulation in brain?

Spongiform encephalopathies

> > Loss of neurones
“Spongiform vacuolation” of brain without immune response

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Clinical presentation of Spongiform encephalopathies?

Rapidly progressive dementia, loss of memory and intellect, personality changes, unsteadiness / clumsiness, myoclonic jerks.

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Prion diseases manifest quickly. True or False?

False

Long incubation period (years).

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Prion transmission?

Not by (direct / indirect) contact / droplet / airborne / fomites / environment
No natural (non-iatrogenic) person-person spread
Iatrogenic transmission (<1%)***** e.g. transplant, transfusion, medical equipment

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2 types of CJD? Differences? Epidemiology?

1) Familial (genetic predisposition): older patients
2) Variant CJD (vCJD): younger patients

No difference between CJD and vCJD in sensitivity to disinfection / sterilization

Difference in the range of tissues that are infectious

Sporadic cause (85%): older (mean 63 years; 1 per million)

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List 4 ways prion disease can be transmitted iatrogenically?

1) Implantation of contaminated grafts: Dura mater, cornea
2) Hormones: human growth hormone, pituitary gonadotrophin
3) Contaminated medical instruments: electrodes in brain, neurosurgical instruments
4) Blood transfusion

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List some precautions that should be taken if a CJD patient requires surgical operation?

 Perform in operating theatre: Last in list, Environment should be readily cleanable

 Use disposable equipment in contact with CSF, blood

 Segregate tissue by decontamination requirement

 Reusable items require special sterilization procedures

 Avoid use of high-speed drill / other aerosol-generating procedures

 Tissue biopsies: consult pathologist in advance regarding fixation

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List some ineffective disinfectants for prions?

 Alcohol 
 Ammonia 
 Formaldehyde
 Glutaraldehyde 
 Hydrogen peroxide
 Iodine
 Phenolics

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List some effective disinfectants for prions (<1hour) ?

 Chlorine >1000ppm (ideally 20,000ppm; 2%) – high concentration hypochlorite*

 Sodium hydroxide 1M*

 Proprietary enzymatic, alkaline detergents (e.g. Steris, Prionzyme)

 96% formic acid (to preserve tissue)

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List some effective disinfectanting processes for prions (>1hour) ?

1) Immerse in 1M NaOH for 2 hours
2) autoclave 121oC for 30 min

*Autoclave (higher temperature, longer time):
 134oC for >18 min (prevacuum)
 132oC for 60 min (gravity)

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List 4 challenges that antivirals face in managing viral infections? (Can it kill viruses? How effective? Latency issues?)

Very few virus-specific “targets”: Mechanism of virus replication involves host cell
Often need to commence antiviral treatment early in illness in order to make a clinical impact
Blocks viral replication, but not virucidal
Cannot eliminate virus latency

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List the 6 stages of viral replication?

Attachment
Penetration/ fusion
Uncoating
Transcription, Translation
Nucleic acid replication
Viral assembly, release

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List 2 drugs that target viral attachment. Give virus name in clinical use.

Maraviroc (CCR5) = HIV

Sialidase (e.g. DAS181) = Influenza, parainfluenza

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List 1 drug that target viral penetration/fusion . Give virus name in clinical use.

Enfuvirtide

HIV

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List 2 drugs that target viral uncoating. Give virus name in clinical use.

 Amantadine
 Rimantidine

Influenza A (most viruses now resistant)

List 2 drugs that target viral transcription, translation. Give virus name in clinical use.

Ribavirin HCV, RSV

Interferon HCV, HBV

Give 3 subtypes and examples of antivirals against nucleic acid replication?

1) Nucleoside analogues (e.g. acyclovir, ganciclovir): competitive DNA polymerase inhibitor
2) Directly blocks viral DNA polymerase (e.g. Foscarnet)
3) RNA polymerase inhibitors (e.g.: Baloxavir marboxyl, T705 (favipiravir))

RNA polymerase inhibitors antivirals is given for which virus?

Influenza

Give 3 subtypes and examples of antivirals against virus assembly and release?

1) HIV protease inhibitor = Saquinavir, Indinavir, Ritonavir, Nelfinavir
2) HCV protease inhibitors, e.g.: Boceprevir, Telaprevir
3) Neuraminidase inhibitors, e.g.: Oseltamivir,* Zanamivir, Lananimivir = Influenza

MoA of Acyclovir?

Only act on virus-infected cell

Acyclovir > [Viral thymidine kinase] > ACV monophosphate > [cell enzyme] > ACV triphosphate (active)

selective inhibition of viral DNA polymerase

When to give IV acyclovir, when to give oral?

HSV1, HSV2 (oral, low dose)

VZV (oral, high dose)

CMV (intravenous)

HSV enephalitis = IV

List 2 viral mutations that cause resistance against acyclovir and 2 drugs to circumvent the resistance?

1) Mutant viral thymidine kinase enzyme: block
Acyclovir to ACV monophosphate conversion

> > use Cidofovir (= monophosphate nucleotide analogue, bypass TK)

2) Mutant viral DNA polymerase: No longer prefers acyclovir triphosphate
» use Foscarnet

What form of acyclovir has improved bioavailability? Pharmacokinetics? Spectrum the same?

Valaciclovir: = valine ester of acyclovir = pro-drug of acyclovir: - Increased absorption in GI = better oral bio-availability (1 g 3x/day) - Broken down completely to acyclovir instantaneously in blood Same spectrum as ACV

Indication for Ganciclovir? Route of admin?

Treatment, prophylaxis of CMV disease in immunocompromised Active vs HSV, VZV but no better than ACV with heavy renal/ CNS side effects IV or Intra-ocular for retinitis (oral = poor availability)

Major side effect of Ganciclovir and resistance?

Resistance : CMV enzyme UL97, Viral DNA polymerase Major side effect: myelosuppression (do not only target infected cells)

What form of Ganciclovir has improved oral bioavailability? MoA? Indication?

Valganciclovir Valine ester of ganciclovir rapidly converted to ganciclovir in intestinal epithelial cells. – CMV prophylaxis (once daily dosing) in transplant Pts – Therapy of non-severe CMV in organ transplant Pts – Treatment of CMV retinitis in AIDS

Foscarnet, Cidofovir can cover what virus that Acyclovir, Valaciclovir, Famciclovir cannot?

Acyclovir, Valaciclovir, Famciclovir: – HSV, VZV Foscarnet, Cidofovir: – CMV**, HSV, VZV

Foscarnet, Cidofovir advantage and disadvantage against Ganciclovir ?

Advantage = less myelotoxic Disadvantage = more renal toxicity

Mechanism of HIV replication?

RNA virus uses own reverse transcriptase to copy RNA genome into DNA (cDNA) >> integrated into host cell genome (proviral DNA) >> may remain latent / direct active viral replication

List 2 classes of Anti-retroviral drugs and give examples.

1. Nucleoside / nucleotide reverse transcriptase inhibitors (NRTI): Zidovudine, Lamivudine, Abacavir, Tenofovir 2. Non-nucleoside inhibitors of reverse transcriptase (NNRTI): Nevirapine, Efavirenz

MoA and side effect of Zidovudine?

MoA: ZDV is activated by both normal and infected cells: ZDV >> ZDV monophosphate >> ZDV triphosphate >> Inhibition of viral (and normal cell) polymerase & reverse transcriptase Side effects: - Non- specific inhibition of normal cell polymerase= myelosuppression - RNA virus resistance

Integrase inhibitor example?

raltegravir

Define HAART therapy.

Highly active anti-retroviral therapy Use multiple drugs blocking different sites of viral replication cycle = minimise development of drug resistance Typical 1st line: reverse transcriptase inhibitors + protease inhibitors

Indication of Ribavirin?

Respiratory Syncytial Virus Indicated in RSV in pre-engraftment stem cell transplant patients use by aerosol in patients at high risk

MoA of interferons?

Direct immune system: - Produce anti-viral protein - Block viral RNA transcription, protein synthesis - Augment immune response

Which type of interferon is used as an antiviral?

Type 1: alpha, beta Type 3: Lambda Type 2: Gamma – made by immune cells, modulates immune cells. Type 1: IFNa, B are used

MoA of Interferon-alpha. What is the purpose of Peg-IFN over normal IFN?

Alpha: Blocks viral RNA transcription, protein synthesis and augments immune response Peginterferon-α2a or 2b: interferon conjugated with polyethylene glycol/ PEG>> prolongs persistence of drug in blood

Clinical use of IFN therapy?

– Chronic hepatitis B (together with lamivudine) – Hepatitis C (together with ribavirin and new protease inhibitors- Boceprevir, Telaprevir)