MICROBIOLOGY - viruses, testing methods, sterilization, antimicrobials (IAS50, 51, 60(antimicrobial type part) Flashcards
Virus genetic material? What is the genetic material covered by
How can the covering be destroyed
DNA or RNA, enclosed in capsid
capsid can be destroyed by heat or bleach (NaOCl)
Some viruses have lipid envelope - where is it derived from and how can it be destroyed
Cell membrane of host cell (essentially a phospholipid bilayer)
destroyed by soap, alcohol, detergent
Define defective viruses and give an example
Defective viruses: those that do not contain all the genes that code for proteins for viral replication so have to depend on helper viruses
eg hepatitis D requires hepatitis B antigen as its own surface antigen but does not have the gene and cannot produce it on its own - so hep D can only coexist with hep B
Lytic cycle?
1) virus attaches onto cells at receptors
2) virus penetrates cells, injecting genetic material (RNA into cytoplasm, DNA into nucleus)
3) viral protein synthesis and nucleic acid replication
4) assembly of nucleic acid and viral proteins to new virions
5) release of virions from cell (may lead to cell death)
Synthesis of viral nucleic acids, viral proteins for DNA and RNA virus?
DNA virus: viral DNA self replicates > transcription to mRNA > translation to form new viral proteins
RNA virus:
positive sense RNA: RNA replicates itself, directly undergoes translation to form new viral proteins
negative sense RNA: RNA undergoes transcription to +ve sense RNA by RNA-dependent RNA polymerase > translation (original viral RNA replicates itself)
Retroviruses: 1) reverse transcription to proviral DNA > 2) transcription to viral mRNA by transcriptase > 3) translation to viral proteins (original viral RNA replicated)
How do viruses with latent cycle cause recurring infections
Eg herpesviruses: virus genome in circular episomes integrated into host chromatin - so when immune system immunity becomes lower (eg stress) virus travels down nervous pathways to trigger symptoms
How do oncogenic or retroviruses exert effect
Viral genome integrated into host genome
Eg: HIV virus infects CD4+ cells and injects its genome into the cells - infected CD4+ cells produce the virus and immune system becomes compromised - so immediately receive antiretroviral treatment for 4 weeks upon exposure to try eliminate infected cells and the affected genome)
How to classify viruses:
1) DNA or RNA
2) No. of strands OR for RNA: +ve or -ve sense
3) Enveloped or unenveloped
DNA viruses - classify them and give examples
DNA viruses:
1) Double stranded, enveloped: e.g. hepadnaviruses, herpesviruses, poxviruses
2) Double stranded, unenveloped: eg e.g. adenoviruses, papillomaviruses, polyomaviruses
1) Single stranded, unenveloped: e.g. parvoviruses
RNA viruses: classify them and give examples
+ve sense RNA:
Unenveloped: e.g. caliciviruses, picornaviruses
Enveloped: e.g. coronaviruses, flaviviruses, togaviruses
-ve sense RNA:
Enveloped: e.g. arenaviruses, bunyaviruses, filoviruses, orthomyxoviruses, paramyxoviruses, rhabdoviruses
both +ve and -ve:
Double capsid: Reoviruses
RNA via DNA (retroviruses): enveloped
Define: incubation period, period of infectivity
Incubation period: The time interval between virus entry and the commencement of disease symptoms
Period of infectivity: The time interval in which there is virus shedding; dependent on the virus
Compare pathogenesis: localized infections and systemic infections
Localized: The virus multiplies at the epithelial surface at or near its site of entry to the body
Systemic:
Initially, the virus multiples locally at the site of entry.
It then spreads by blood (viraemia; chronic: e.g. hepatitis B, HIV) or other means (e.g. along peripheral nerves) to distant sites and localizes in target organs (tissue tropism).
It may lead to organ damage and hence major diseases
Viral culture/transport medium components?
Live cell culture/infected animal
transport medium need: pH buffer, pH indicator, antibacterials, proteins to maintain virus stability
Which form of PCR for RNA viruses
reverse transcriptase PCR
Groups of viruses causing skin rash?
Herpesvirus, enterovirus, vaccine-preventable virus
Herpesvirus classification?
Symptoms/morphology/transmission method for each?
HSV1, HSV2, VZV, cytomegalovirus
HSV1: cold sores, usually transmitted via oropharyngeal secretions
● primary infection and reactivation most commonly orofacial lesions
HSV2: usually sexually transmitted
● primary infection and reactivation most commonly anogenital lesions
VSV: varicella zoster virus
■ airborne transmission
■ primary infection: chickenpox
■ reactivation: herpes zoster (shingles)
ABOVE 3 ALL LATENT IN SENSORY GANGLIA
Cytomegalovirus:
latent in Haematopoietic progenitor cells
causes Infectious mononucleosis like syndrome, congenital CMV disease
severe/disseminated reinfections (reactivations) in immunosuppressed but asymptomatic otherwise
Infectious mononucleosis viral causes?
CMV, HIV, other herpesviruses
Enterovirus - name some examples and what diseases they cause that give skin rash symptoms
Enterovirus A71: Hand foot mouth disease
Parvovirus B19: erythema infectiosum (slapped cheek syndrome)
Name some vaccine-preventable viruses causing skin rash
How is mpox most commonly transmitted?
measles, mumps, rubella, mpox
mpox: MSM
Name 5 big groups of respiratory viruses?
Name 4 other groups of viruses that can also cause respiratory diseases?
Influenza A and B viruses, respiratory syncytial viruses, SARS-CoV-2, adenoviruses, rhinoviruses/enteroviruses
parainfluenza, HMPV (human metapneumovirus), MERS, other coronaviruses (eg HKU1, NL63, OC43, 229E)
SARS-CoV-2: how to test for it - for PCR, which genes are targeted?
why is it called coronavirus
What type of virus (based on genetic material classification) is it
What does transverse chest CT scan show for patients with viral pneumonia
Testing by RT-PCR, RAT
E (envelope), N (nucleocapsid protein), RdRp (polymerase)
Coronavirus because it has spikes on surface shaped like crowns
-ve sense RNA enveloped virus
focal ground glass changes
Respiratory syncytial viruses (RSVs):
Name 1 disease it can cause
What does it form in cell culture
Seasonality and peak?
Acute bronchiolitis (blockage of bronchioles) in young children
syncytium, multinucleated giant cells
All year seasonality, peak in summer
Influenza:
1) How many types? Which are more serious?
2) Structure (the 2 that make up naming of influenza viruses)? What are the components targeted by?
3) Define: drift and shift
1) 3 types, A/B/C, A and B more serious
2) H: hemagglutinin - for entry to cells (targeted by serum nAb)
N: neuraminidase for cell exit (target by antivirals)
(so HxNx)
3) Drift: slight mutations in existing influenza strains causing seasonal influenza
Shift: major changes, usually involving recombination with animal influenza, causing pandemics (eg avian H3Nx with human H2N2 leading to human H3N2)
Diseases caused by influenza?
Medication to treat influenza?
self-limiting URTI, LRTI, chronic illness exacerbation, encephalitis, myocarditis
In children taking aspirin: Reyes’ syndrome
Oseltamivir (NA inhibitor) / Zanamivir
