viral pathogenesis

Question 1

What are the requirements for successful infections?

Answer 1

dose
access to target cell
absent or insufficient host immunity

Question 2

Why is the knowledge of incubation periods important?

Answer 2

aids diagnosis and is essential tool in tracing spread of disease outbreaks

Question 3

What are the different lengths of incubation?

Answer 3

short (<1 week) - localised infections - Arboviruses

medium (7-21 days) - generalised infections - Measles

long (weeks to month) - Rabies

very long (years) - usually fatal - prion disease

Question 4

Why is knowledge of disease patterns important?

Answer 4

aids in disease management and public health response

Question 5

What are the different types of disease patterns?

Answer 5

Acute none persistent - rapid and self limiting
Latent - persistence of viral genome in the host cell
Persistent - asymptomatic
Persistent pathogenic
Insidious infections with fatal outcomes

Question 6

What is viral pathogenesis?

Answer 6

Complex interaction between virus and host that results in disease

Question 7

What is pathogenicity?

Answer 7

the comparison of the severity of disease caused by different microorganism

Question 8

What is virulence?

Answer 8

the comparison of the severity of disease caused by different strains of the same microorganism

Question 9

What are common sources of animal-to-human transmission?

Answer 9

rodents
bats

Question 10

Where can viruses invade a host?

Answer 10

entry through the skin
entry through mucous membranes (most)

Question 11

What are the skin entry routes?

Answer 11

abrasions
inoculation and contaminated needles
insect or animal bites

Question 12

What are the entry routes via mucous membranes?

Answer 12

respiratory tract
gastrointestinal tract
conjunctiva
genital tract
transplacental

Question 13

What happens after viruses reach the basement membrane?

Answer 13

directional release of virus particles from polarised cells at the mucosal surface

Question 14

How are virus particles released from polarised cells?

Answer 14

Apical release (no underlying penetration)
Basolateral release (penetrates underlying, may allow systemic spread)
Both released (= disseminated infection)

Question 15

What is haematogenous spread?

Answer 15

disseminate by entering bloodstream

Question 16

How can viruses be taken up?

Answer 16

by local lymphatic vascular system, replicate in endothelial cells or inoculation by a vector bite

Question 17

What is viraemia?

Answer 17

describes the presence of infectious virus particles in blood

Question 18

What is active viraemia?

Answer 18

produced by virus replication

Question 19

What is passive viraemia?

Answer 19

virus particles are introduced into the blood without viral replication at the site of entry

Question 20

What is secondary viraemia?

Answer 20

subsequent disseminated infections

Question 21

What are cellular factors for viral invasion?

Answer 21

Presence of appropriate receptors
Physical and molecular environment
Morphological changes in host cell caused by viral invasion (cytopathic effects)

Question 22

What are some cytopathic effects?

Answer 22

lysis
syncytium formation

Question 23

What is syncytium formation?

Answer 23

fusion of an infected cells with neighbouring cells leading to the formation of multi-nucleate enlarged cells or syncytia

Question 24

What are the different types of skin rash’s (exanthem features)?

Answer 24

enanthem
vesicular eruptions
maculopapular rash
purpuric rash
haemorrhagic rash

Question 25

What are Maculopapular rashes?

Answer 25

destruction of infected cell by CTL

Question 26

What is a purpuric rash?

Answer 26

thrombocytopenia

Question 27

What can cause a Haemorrhagic rash?

Answer 27

disseminated intravascular coagulopathy

Question 28

Where does dissemination of infection occur?

Answer 28

localised at the site of entry
spread from site of entry to one or more distant site

Question 29

What are the important target organs for dissemination?

Answer 29

lungs
liver
central nervous system

Question 30

What are some CNS viral infections?

Answer 30

aseptic meningitis
encephalitis
myelitis
paralysis

Question 31

What is aseptic meningitis?

Answer 31

inflammation of meninges

Question 32

What is encephalitis?

Answer 32

infection of the brain

Question 33

What are some symptoms of Encephalitis?

Answer 33

headache, fever, confusion, drowsiness, convulsions, seizures, hallucinations

Question 34

What is acute flaccid paralysis?

Answer 34

acute onset of flaccid paralysis in one or more limbs

Question 35

What causes acute flaccid paralysis (AFP)?

Answer 35

may be caused by anterior horn cell infection with wild or vaccine polio virus

Question 36

What can primary HIV disease lead to?

Answer 36

AIDS dementia complex (brain)
vacuolar myelopathy (spinal cord)
peripheral neuropathy (nerve)
meningitis (acute or chronic)

Question 37

What are the 7 stages of HIV replication cycle?

Answer 37

binding
fusion
reverse transcription
integration
replication
assembly
budding

Question 38

What is the measles infection pathway?

Answer 38

1. virus entry
2. primary replication
3. spread and cell tropism
4. cell injury and clinical illness
5. recovery from infection
6. virus shedding and transmission

Question 39

How can a virus shed?

Answer 39

from primary site of multiplication or from target organ

Question 39

How can a virus shed?

Answer 39

from primary site of multiplication or from target organ

Question 40

What is R0?

Answer 40

is the average number of secondary cases generated by one primary case in a susceptible community