9 - Viral infection and Prions*

Question 1

Requirements for successful infection

Answer 1

• Dose (enough virus)
• Access to target cells (susceptible, permissive)
• Absent or insufficient host immunity

Question 2

Viral pathogenesis

Answer 2

The complex interaction between virus and host that results in disease

Question 3

Pathogenicity

Answer 3

The comparison of the severity of disease caused by different microorganisms

Question 4

Virulence

Answer 4

Comparison of the severity of disease caused by different strains of the same microorganisms

Question 5

How can a virus enter through skin

Answer 5

• Abrasions (HPV)
• Inoculation with contaminated needles (HIV, Hepatitis B and C)
• Insect or animal bites (rabies)

Question 6

How can a virus enter through mucous membranes

Answer 6

• Respiratory tract (Influenza, Corona)
• Gastrointestinal tract (eg. Poliovirus)
• Conjunctiva (Adenoviruses)
• Genital tract (Herpes, HIV)
• Transplacental, congenital and vertical (HSV, Rubella, CMV)

Question 7

Virus dissemination after infection

Answer 7

• Localised at site of entry
• Spread from site of entry to one or more distant sites

Question 8

Disseminated viruses

Answer 8

Viruses that have spread beyond the primary site (if many organs are infected becomes systemic)

Question 9

What are the important target organs of infection

Answer 9

• Skin (measles)
• Lungs (pneumonia)
• Liver (yellow fever)
• CNS (polio, rabies)

Question 10

Example of transplacental infection

Answer 10

Zika virus

Question 11

Viral selective advantage

Answer 11

Drug stops replication of susceptible variants, favouring resistant variant to grow and dominate

Question 12

Viral classification suffixes

Answer 12

• Order (‘-virales’)
• Families (‘-viridae’)
• Genera (‘-virus’)

Question 13

How are viruses visualised

Answer 13

Using electron microscope. Does not require organism specific reagents (like in serological or biochemical identification)

Question 14

Host range

Answer 14

Spectrum of host cells the virus can infect (invertebrates, vertebrates, plants, fungi and bacteria)

Question 15

How is host range determined

Answer 15

by virus requirements for attachment to host cell

availability within host cell of factors required for replication

Question 16

Zoonotic diseases

Answer 16

Viruses that cross species barriers

Question 17

Smallpox

Answer 17

Caused by infection with variola virus. First human disease successfully eradicated by vaccination

Question 18

Influenza

Answer 18

• In 1918 after WW1 spread around the globe in a series of waves killing > 50 million people
• No vaccine effective against all influenza as new strains continuously emerge

Question 19

SARS-CoV

Answer 19

A novel coronavirus associated with severe acute respiratory syndrome.

Highly contagious, reservoir host identified as bats.

Question 20

What is a prion

Answer 20

Proteinaceous infectious particle.

Abnormal pathogenic agents that are transmissible and able to induce abnormal folding of prion proteins that are found abundantly in brain. Results in large vacuoles in the brain

Question 21

what are prions distinguished by

Answer 21

• Long incubation periods
• Characteristic spongiform changes associated with neuronal loss
• Failure to induce an inflammatory response

Question 22

Cruetzfeldt-Jakob disease (CJD)

Answer 22

• Dementia
• Rapidly progressive and always fatal
• Infection leads to death usually within one year of onset of illness (4-5 months)

Question 23

vCJD human form of BSE

Answer 23

• Varient of CJD
• Prominent psychiatric/behavioural problems, delayed neurological signs
• Infections leads to death usually around 13-14 months post onset of illness

Question 24

Name another disease caused by prions

Answer 24

Fatal familial insomonia

Question 25

name three diseases caused by prions in animals

Answer 25

• Scrapie in sheep
• CWD (chronic wasting disease)
• Mad cow disease

Question 26

Mad cow disease (BSE)

Answer 26

• Originated as a result of feeding cattle meat and bone meal that contained BSE infected products
• Cattle experience progressive degeneration of nervous system and must be sacrificed

Question 27

What does BSE stand for

Answer 27

Bovine spongiform encephalopathy

Question 28

Kuru

Answer 28

First identified transmissible spongiform encephalopathy

Transmitted orally via the consumption of infected meat/nervous tissue - endocannibalism