lesson five

Question 1

viruses

Answer 1

• infectious particles
  -must be treated using different therapeutic strategies than
  other microorganisms because they are different in
  makeup and structure

Question 2

transmission of viruses

Answer 2

blood transfusion, mucus droplets, aerosols, fomites,
air (airborne), water, food, vectors

Question 3

Virus Size

Answer 3

• smaller than most bacteria
• always obligate intracellular parasites

Question 4

virion

Answer 4

complete infectious viral particle with nucleic acid surrounded by protein coat

Question 5

viral structure

Answer 5

• RNA or DNA and capsid (protein coat) comprised of capsomeres (protein molecules)
• complete unit: nucleocapsid
• some viruses have “lipid envelopes” outside of the
  nucleocapsid
• glycoproteins or spikes inserted in enveloped or capsid

Question 6

virus host range

Answer 6

• different viruses can infect every life form
• usually fairly specific host range or specificity

Question 7

bacteriophages

Answer 7

• viruses that infect bacterial cells and can transfer new genes from one bacteria to another
• can transfer genes for production of toxin

Question 8

classifying viruses

Answer 8

• viruses are grouped into families on basis of DNA or RNA genome composition
• RNA viruses are known for their ability to mutate quickly

Question 9

DNA viruses

Answer 9

1. Papillomaviridae (HPV)
2. Adenoviridae (adenovirus)
3. Hapadnaviridae (hepatits B virus)
4. Herpesviridae (HSV-1, HSV-2, HHV-3…)
5. Poxviridae (smallpox, monkeypox)
6. Parvoviridae (B-19)

Question 10

Viral infection: attachment and penetration into host cell

Answer 10

a) virus must attach to host cell, usually to receptors
b) two processes for penetration of the virus into the host cell: Fusion and Pinocytosis

Question 11

viral infection: replication of the genome

Answer 11

• DNA forms the genome of all organisms
• Transcription of the DNA gives rise to a RNA molecule that is almost an
  exact copy of the DNA
• protein is synthesized

Question 12

what is the goal of a virus

Answer 12

to replicate itself

Question 13

can viruses have two types of nucleic acid

Answer 13

• viruses have only ONE type of nucleic acid (DNA or RNA)

Question 14

DNA viruses replication

Answer 14

Host cell DNA polymerase may be used directly
to make more virus DNA (if replic. in host cell nucleus)
viral DNA → viral DNA

Question 15

RNA viruses replication

Answer 15

Virus must carry its own RNA polymerase
enzyme to produce RNA from viral RNA (no RNA
polymerase in host cells)
viral RNA → viral RNA

Question 16

retrovirus replication

Answer 16

carries its own reverse
transcriptase enzyme in the virus capsid:
viral RNA → viral DNA integrated into the
chromosome → viral RNA

Question 17

assembly of new virus

Answer 17

• Association of newly replicated RNA or DNA (nucleic acid) with newly made
  viral proteins results in new nucleocapsids

Question 18

release of new enveloped virus

Answer 18

envelope components are produced and inserted into the host cell plasma membrane, the viral particle then attaches to the plasma membrane and buds through

Question 19

fuzeon (antiviral drug)

Answer 19

stops entry (fusion) of HIV into cells

Question 20

acyclovir (antiviral drug)

Answer 20

stops replication of herpes viruses by interfering
with the viral DNA polymerase

Question 21

tamiflu (antiviral drug)

Answer 21

stops budding/release of influenza
virus from host cell

Question 22

acute or productive infection

Answer 22

• virus replicates, produces many virions
• host cell often killed= lytic infection

Question 23

latent infection

Answer 23

viral genome persists in host cell but does not replicate- provirus

Question 24

chronic infection

Answer 24

virus replicates without causing host cell lysis and can persist for long periods of time

Question 25

what virus causes acute chickenpox infection

Answer 25

Caused by an enveloped DNA virus, HHV-3, sometimes called “varicella"

Question 26

chickenpox acute infection symptoms

Answer 26

- fever, itchy rash - rash is spread on trunk and head - virus particles in rash can escape and infect - skin vesicles always present in different stages of lesion formation - When lesions heal, the virus travels up the nerve that ennervates the skin at the site of the lesion and makes a home in the peripheral nerve ganglion where it remains latent

Question 27

chickenpox latent infection

Answer 27

- virus is present but no replicating until triggered by external factors, then travels down nerve to skin and reactivates

Question 28

what is reactivation known as in HHV-3

Answer 28

shingles or zoster

Question 29

shingles or zoster

Answer 29

- reactivation of the virus as it travels back down the nerve to skin from the site of latency - begins as a local skin rash - characterized by confluent rash and pain - untreated rash lasts 2-5 weeks, infectious to those who have not had chicken pox

Question 30

chicken pox complications

Answer 30

- most common in immunocompromised is secondary bacterial infection - CNS disease: encephalitis, meningitis, myelitis

Question 31

zoster complications

Answer 31

- PHN (Post Herpetic Neuralgia) most common complication - 25-50% of patients >50 yrs develop PHN - Pain that persists for months or years - Can cause permanent nerve damage so important to get treatment (acyclovir) within 48-72 hours of symptoms appearing

Question 32

prevention of chickenpox

Answer 32

active immunization: - live attenuated vaccine passive immunization: - effective up to 3 days post-exposure - VZIG antibodies to the virus - normally for immunocompromised exposed children and neonates born to mothers with varicella

Question 33

chickenpox

Answer 33

lesions are in different stages of development

Question 34

smallpox

Answer 34

all lesions are in the same stage of development

Question 35

oncogenic viruses

Answer 35

- Some viruses can “transform” normal host cells to cancer cells - Not all “transformed” cells become cancerous e.g. wart virus: often benign tumours- Cancer-producing viruses can be RNA or DNA viruses

Question 36

PCR viral diagnosis

Answer 36

polymerase chain reaction - molecular biology technique used to detect the genes in an organism

Question 37

prions

Answer 37

- protein misfolding disease - self protein becomes changes and nonfunctional - prions are misfolded proteins that act as infectious agents in susceptible exposed animals

Question 38

human prion disease

Answer 38

always fatal

Question 39

human prion disease signs

Answer 39

- ataxia - Cortical visual symptoms - Progressive dementia - Myoclonus - Akinetic mutism average death time after onset :4 months