Morphology and biology of viruses

Question 1

What are the criteria for virus classification?

Answer 1

• Type of genome (DNA/ RNA, ds/ss)
• Replication strategy
• Structure and size of virion - envelope?
• Host rage
• Tissue tropism
• Pathogenicity
• Mode of transmission
• Physiochemical properties
• Antigenic properties

Question 2

What is the structure of herpes?

Answer 2

• icosahedral nucleocapsid
• dsDNA linear
• Enveloped

Question 3

What is the structure of HIV?

Answer 3

• Enveloped
• Viral gp120 and gp41
• 2 copies of RNA
• Reverse transcriptase
• Integrase
• Protease

Question 4

What is the structure of hep A?

Answer 4

• Picornaviridae family
• No envelope
• Icosahedral
• ssRNA
• +ve sense

Question 5

How is hep A transmitted?

Answer 5

• Children and young adults
• Mainly foecal-oral
• possible sexual but unlikely

Question 6

What is the structure of hep B?

Answer 6

• Hepadnaviridae family
• Enveloped
• 42nm
• Icosahedral
• Circular DNA, partially ds
• Complete virus and incomplete particles
• Tubular filaments and spherical

Question 7

How is hep B transmitted?

Answer 7

• Young babies - toddlers
• Percutaneous - needles
• Perinatal
• Sexual
• Found in body fluids

Question 8

What is the structure of hep C?

Answer 8

• Flaviviridae family
• Enveloped
• Icosahedral
• ssRNA
• Non-structral protein 1

Question 9

What are some risk factors for hep C?

Answer 9

• IV drug abuse
• Body piercings and tattoos
• Needle stick injury
• mother to baby
• sexual transmission

Question 10

How is Hep C transmitted?

Answer 10

• Any age
• Percutaneous
• possible for perinatal and sex

Question 11

What is norovirus?

Answer 11

• Common cause of infectious gastroenteritis -> diarrhoea
• Caliciviridae
• icosahedral
• non-enveloped
• ssRNA

Question 12

What is rotavirus?

Answer 12

• Reoviridae
• dsRNA - 11 segments
• Non-enveloped
• icosahedral
• Causes fever, vomiting, diarrhoea, abdominal pain
• Structural proteins - VP1-7
• non-structural - NSP1-6

Question 13

How does rotavirus replicate?

Answer 13

• Binds to cell with VP7 and VP4 - enters by endocytosis
• Uncoats
• Has VP6 channel, allowing dsRNA to move in and out of virus
• VP1-3 allow transcripton in virus, then sends it to ribosomes of cell to be translated - makes single shelled particles
• These double layered then go to the ER, where they acquire outer shell
• Then get released

Question 14

What is measles virus?

Answer 14

• Enveloped
• ssRNA
• -ve sense
• Paramyxoviridae
• Pleomorphic

Causes

• fever cough, runny nose, red eyes, sore throat
• White spots in mouth
• Rash on face, spreads downwards

Question 15

How is measles transmitted?

Answer 15

• highly contagious

- Transmitted by coughing/ sneezing

Question 16

What is mumps virus?

Answer 16

• Paramyxovirus
• Pleomorphic
• Enveloped
• Helical nucleocapsid
• ssRNA linear genome

Causes
- fever, headache, muscle aches, tiredness, loss of appetite, swollen and tender salivary glands on both sides

Transmitted
- Droplets

Question 17

What is rubella virus?

Answer 17

• Acute viral disease causing fever and rash
• Spread through coughing and sneezing
• Togavirus family
• enveloped
• ssRNA
• icosahedral

Question 18

What is congenital rubella?

Answer 18

• Birth defects if acquired by pregnant woman

- Deafness, cataracts, heart defects, foetal brain damage, liver and spleen damage

Question 19

What is adenovirus?

Answer 19

• Adenoviridae
• No envelope
• Icosahedral
• dsDNA, linear
• Respiratory illness, or gastrenteritis, conjunctivitis, cystitis, rash

Question 20

What is papillomavirus?

Answer 20

• no envelope
• Icosahedral
• circular dsDNA
• Papovaviridae
• Different serotypes - some cause infections in the genital tract
• Cervical cancer

Question 21

What is parvovirus?

Answer 21

non-enveloped

• ssDNA
• Nucleocapsid icosahedral
• Pavovirus B19 can attach to erythrocyte progenitor cells and inhibit erythropoeisis
• shortens life span of RBCs
• mostly in children
• Slapped cheek rash
• may have low-grade fever

Question 22

What is the structure of influenza?

Answer 22

• Orthomixoviridae
• Enveloped
• Has HA, NA, and an ion channel (matrix protein 2, M2)
• Also M1 protein associated with ribonucleoprotein in middle, and the envelope

Question 23

What are the influenza subtypes?

Answer 23

• A - most serious. Animals and birds. Genetic cross-over leads to pandemic
• B - humans - minor outbreaks but not pandemic
• C - mild, only affects humans. Endemic, symptoms similar to the common cold

Question 24

What is the replication cycle of influenza?

Answer 24

• Virus binds to sialic acid via HA - endocytosis
• Virus envelope fuses with the endosome, low pH triggers uncoating
• Viral nucleic acid capsid contains RNA and is released into cytoplasm
• Viral RNA is copied in nucleus - -ve sense so must be transcribed twice
• Once transcribed, mRNA is synthesised and translated in the cytoplasm
• Early viral proteins are transported back into the nucleus as they are needed for transcription and replication (telomerase and ribosomes)
• RNA segments are assembled in the nuclear capsid
• Assembly and budding of new virions out of the plasma membrane

Question 25

What is the current strategy for dealing with influenza?

Answer 25

• Global influenza network (GIN - part of WHO) - estimate the strain of virus before the following season and recommend vaccines
• There are errors in the estimate, time constraints. Third world don’t have resources for this. There can still be antigenic drift, so even if we have the perfect vaccine this can still be inefficient.