viruses

Question 1

what are viruses

Answer 1

-simple acellular infectious pathogens
- incapable of self replication and metabolic activity
-obligate intracellular parasites

Question 2

describe the viral genome

Answer 2

-consists of DNA or RNA (can not be both)
- the DNA or RNA can be linear or circular
-RNA can be ‘+ve sense’ (can synthesise proteins) or ‘-ve sense’ ( needs to covert to +ve sense to allow synthesis of proteins

Question 3

describe the viral components

Answer 3

genome: nucleic acid
capsid: protein coat
nucleocapsid: complete unit of nucleic acid and capsid
- may also contain essential or accessory enzymes to facilitate initial replication
can be naked or enveloped

Question 4

define virion

Answer 4

fully assembled infectious extracellular particle
(intracellular viral structures are not always fully assembled)

Question 5

describe the capsid structure

Answer 5

composed of caposomeres- several different polypeptides grouped together
distinctively symmetrical - helical or icosahedral

Question 6

describe enveloped viruses

Answer 6

• characterised by a phospholipid bilayer derived from the host cell
  plasma membrane, Golgi apparatus, ER, nuclear membrane
  -composed of lipids, viral proteins and glycoproteins
• host cell membrane proteins replaced by virally encoded glycoproteins (spike proteins)

Question 7

what are viral attachment proteins

Answer 7

• viruses that express glycoproteins which facilitate host cell entry.
  -alongside capsid proteins in naked viruses or anchored in the phospholipid bilayer of developed viruses
• different viruses express different glycoproteins which attend to specific host cell receptors.
• these spike glycoproteins confer virus antigenicity

Question 8

viral tropism

Answer 8

• most viruses infect only specific types of cells and tissue in one host
• viral tropism: ability of a given virus to productively infect a:
  -particular cell (cellular tropism)
  -tissue (tissue tropism)
  -host species (host tropism)

Question 9

modes of transmission

Answer 9

-oral transmission (hepatitis A)
- droplet transmission (influenza)
- direct inoculation (yellow fever)
-sexual transmission (HIV)
-direct skin contact (herpes)

Question 10

nucleocapsid composition pt2

Answer 10

-nucleocapsid can either be naked or enveloped
-both contain viral attachment protein
- viruses can be classified using: size, genetic material, capsid structure and symmetry, naked or enveloped.

Question 11

what are bacteriophage

Answer 11

complex viral structure
viruses that infect bacteria

Question 12

list respiratory illnesses and its cause

Answer 12

resp illnesses can arise from rhinovirus, influenza, coronavirus and parainfluenza
-common cold, bronchiolitis, croup, viral pneumonia

Question 13

coronavirus

Answer 13

large family of viruses including SARS-CoV, MERS-CoV and SARS-CoV-2
-good example of zoonis: and infection which is passed from non human to human host
-this can expose humans to novel viruses

Question 14

Influenza

Answer 14

• Type A+B - human disease
  -Type B+C - limited genetic diversity
• Type D - only infects cattle
• ## sudden onset of fever, chills, headache, muscle pain, extreme fatigue, dry cough, sore throat, blocked nose.

Question 15

Influenza A

Answer 15

-zoonotic infection (between species)
-broad host range
- viral sub-types distinguished according to surface proteins
>HA- Haemagglutinin (17 subtypes)
>NA- Neuraminidase (9 subtypes)

Question 16

Human Herpesviruses

Answer 16

-cold sores, chicken pox and shingles
- all herpesviruses persist for the lifetime of the host
-establish a latent (non replicating) state
- may be reactivated under certain conditions

Question 17

Measles

Answer 17

-flu like illness, fever, cough, conjunctivitis
- rash, spots inside the mouth
-encephalitis

Question 18

Mumps

Answer 18

-swelling of face, ears, headaches and fever
-viral meningitis

Question 19

Rubella

Answer 19

-rash, aching joints, fever
-can cause congenital rubella syndrome
-80-90% of infections in early pregnancy cause miscarriage or stillbirths

Question 20

MMR vaccination coverage

Answer 20

anti- vaccination movements perpetuate misinformation about safety of vaccines
- highlights the importance of clear, evidence-based science communication

Question 21

HIV/AIDS

Answer 21

• human immunodeficiency virus
• single stranded +ve sense RNA retrovirus
  -spreads through the body fluids where the body immune cells are found (CD4+ cells)
  -acute infection: flu like illness
• clinical latency: HIV inactivity or dormancy
  AIDS: CD4 count bellow 200 cells/mm^3

Question 22

Opportunistic Pathogens

Answer 22

• epstein-barr: virus infection (hairy leukoplakia) raised white lesions of oral mucosa
• fungal infection: oral candidates
  -HHV-8 Virus- Kaposi’s sarcoma Brown pigmented lesions
  -Fungal infection_ Pneumocytis pneumonia
  extensive infiltrate in both lungs

Question 23

Zika virus

Answer 23

• outbreaks in pacific, region South+Central America, Caribbean, Africa
• spread by infected mosquitos and sexual intercourse
  -commonly asymmetrical, symptoms: fever, rash, headache, joint pain, conjunctivitis and muscle pain
  -passed from pregnant women to foetus (congenital Zika syndrome- microcephaly) + associated with Guillian-Barre syndrome

Question 24

Ebola virus

Answer 24

zoonotic origin
- human and non human primates (monkeys, gorillas and chimps)
-5 known Ebola viruses species, 4 cause disease in humans
-fast symptoms onset including nausea, blood in faeces and bleeding from ears, eyes, nose and mouth
-transmitted by direct contact

Question 25

stages of viral replication

Answer 25

1. attachment/absorption 2. penetration 3. uncoating 4.replication/synthesis 5. assembly 6. release

Question 26

viral genetic replication

Answer 26

- viruses can exhibit single stranded DNA and circular DNA genomes -these can be transcribed into mRNA by viral RNA polymerase -viral mRNA genomes have many types of replication

Question 27

DNA VS RNA viruses replication

Answer 27

DNA: replicates in the nucleus RNA: replicates in the cell cytoplasm

Question 28

Cellular outcomes of viral infections

Answer 28

- virus release and host cell destruction aka cell lysis (polio) - exit by budding (influenza) - exist in host cell cytoplasm and release by exocytosis (herpes) -incorporated into the genome (retroviruses and hep B) -oncogenic viruses, stimulate uncontrolled cell growth and can lead to cancer (HPV)

Question 29

retrovirus case, HIV

Answer 29

- enveloped retrovirus virus -+ve sense ssRNA viral genome encodes 9 genes -HIV expresses 72 transmembrane glycoprotein antigens -also expresses a matrix and capsid protein - enzymes, reverse transcriptase, integrase and protease are found within the nucleocapsid.

Question 30

HIV infection stages

Answer 30

1. HIV infects T lymphocytes and monocytes (macrophages) through the interaction of gp120 and the CD4 receptor 2. After attachment. the nucleocapsid penetrates the cell membrane 3. The ssRNA genome is replicated as dsDNA 4. HIV integrase incorporates viral DNA into the host DNA 5. Viral DNA is transcribed and translated by the host, and HIV proteases process mature HIV proteins 6. Mature HIV virions are formed from the host plasma membrane.

Question 31

Virale genome variation

Answer 31

-viral genome can vary between replication cycles (in host) or between hosts as the virus passes through a host population - the do this due to evolutionary pressure from host immune systems and antiviral drugs - 3 molecular mechanism that can cause viral genome variation: mutation, recombination and gene switching/ reassortment

Question 32

Rna vs Dna viruses mutation (viral genome variation)

Answer 32

rna viruses mutate faster than DNA viruses SS mutate faster than DS smaller viral genomes mutate faster than larger viral genomes - this generates both advantageous ada deleterious genomic changes

Question 33

viral mutations

Answer 33

-insertion, deletion and substitution occur frequently in viral genomes - RNA dependent RNA polymerase has no proof reading or correction ability (compared to DNA polymerase) - small mutations within antigenic genes allow viruses to evade host immune systems, called antigenic drift, drives the need for viral genome surveillance

Question 34

gene recombination and reassortment

Answer 34

- if two stains of a virus infect a host recombination and/or reassortment can occur -both methods result in extensive genome variation called antigenic shift

Question 35

Gene recombination vs reassortment

Answer 35

recombination- exchange of entire genes between two strains reassortment- exchange of entire segments of genome between strains

Question 36

Influenza

Answer 36

-exhibits both antigenic drift and antigenic shift has 8 segments of -ve sense single stranded RNA -susceptible to insertion, deletion and substitution mutations -able to infect and co-infect multiple species -leads to zoonotic spread of new strains

Question 37

antigenic shift and drift in influenza

Answer 37

antigenic shift of entire segments of influenza genome can occur during co-infection -antigenic drift of the HA and NA glycoproteins causes the repeat outbreaks of seasonal flu