12 - Viral Pathogenesis

Question 1

Requirements for successful infection

Answer 1

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

Question 2

Short incubation period

Answer 2

• <1 week
• Localised infections
• Arboviruses (viruses transmitted by mozzies)

Question 3

Medium incubation period

Answer 3

• 7-12 days
• Generalised infections
• Measles

Question 4

Long incubation periods

Answer 4

• Weeks to months
• Rabies

Question 5

Very long incubation periods

Answer 5

• Years
• Usually fatal
• Prion diseases

Question 6

Latent

Answer 6

Persistence of viral genome in the host cell and periodic virus reactivation

Question 7

Viral pathogenesis

Answer 7

complex interaction between virus and host that results in disease

Question 8

Viral pathogenesis stages

Answer 8

• Entry and primary replication
• Viral spread and cell tropism
• Cell injury and clinical illness
• Recovery from infection
• Virus shedding and transmission
• Host immune response

Question 9

Pathogenicity

Answer 9

the comparison of the severity of disease caused
by different microorganisms

Question 10

Virulence

Answer 10

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

Question 11

Viruses endemic in rodents

Answer 11

Hemorrhagic disease viruses (e.g. Lassa, Junin, Sin Nombre)

Question 12

dead end host

Answer 12

Effect host but not transmitted between hosts

Question 13

Entry through the skin

Answer 13

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

Question 14

Entry through mucous membranes

Answer 14

• Respiratory tract (Influenza)
• Gastrointestinal tract (faecal-oral route, Poliovirus)
• Conjunctiva (Adenoviruses,)
• Genital tract (HSV, HIV)
• Transplacental (congenital, vertical: HSV, Rubella)

Question 15

Apical release

Answer 15

virus does not usually invade
underlying tissues

Question 16

Basolateral release

Answer 16

virus has access to underlying tissues and this may allow systemic spread

Question 17

Which release causes disseminated infection

Answer 17

Release from both apical and basal surfaces

Question 19

Haematogenous spread

Answer 19

• Viruses taken up by the local lymphatic vascular system, replicate in endothelial cells or
  inoculation by a vector bite.
• Access almost every tissue in the host

Question 20

Viraemia

Answer 20

Presence of infectious virus particles in the blood

Question 21

Active viraemia

Answer 21

produced by virus replication

Question 22

Passive viraemia

Answer 22

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

Question 23

Secondary viraemia

Answer 23

subsequent disseminated
infections, appearance of a high concentration of
infectious virus in the blood

Question 24

Cellular factors of viral invasion of the host

Answer 24

• Presence of appropriate receptors
• Physical and molecular environment must enable initial replication cycle (temperature, pH)

Question 25

Lysis

Answer 25

- Virus-encoded proteins may shut down synthesis of cell macromolecules - accumulation of viral proteins may inhibit host cell function. - Cell death is followed by lysis and release of viral particles

Question 26

Syncytium formation

Answer 26

- fusion of an infected cells with neighbouring cells leading to the formation of multinucleate enlarged cells (syncytia) - allows viruses to pass from cell to cell, instead of being released via lysis

Question 27

Ananthem

Answer 27

Rash on mouth mucosa

Question 28

Vesicular eruptions

Answer 28

Viral replication in the skin (herpes)

Question 29

Maculopapular rash

Answer 29

destruction of infected cell by cytotoxic T lymphocytes (measles)

Question 30

Purpuric rash

Answer 30

Thrombocytopenia (Dengue)

Question 31

Haemorrhagic rash

Answer 31

result of disseminated intravascular coagulopathy

Question 32

Disseminated

Answer 32

Spread of virus beyond primary site

Question 33

Systemic

Answer 33

Infecting many different organs

Question 34

Important target organs of dissemination

Answer 34

- Lungs - Liver -CNS

Question 35

Lungs

Answer 35

- Most respiratory infections are localised - Some are generalised (measles)

Question 36

Liver

Answer 36

- Target for hepatitis viruses - Infected during generalised infections (e.g. yellow fiver)

Question 37

CNS

Answer 37

- Access from bloodstream during viraemia (e.g. Polio) - Via peripheral nerves (Herpes, Rabies)

Question 38

Dissemination pathway of herpes

Answer 38

1. Virus inoculated 2. Viral replication in muscle 3. Virus binds to nicotinic acetylcholine receptors at neuromuscular junction 4. Virus travels within axons in peripheral nerves (retrograde axonal transport) 5. Replication in motor neurons of the spinal cord and local dorsal root ganglia and rapid ascent to brain 6. Infection of brain neurons with neuronal dysfunction 7. Centrifugal spread along nerves to salivary glands, skin, cornea

Question 39

Aseptic meningitis (not caused by pyogenic bacteria)

Answer 39

- Inflammation of the meninges - Viral infection is the most common (enterovirus)

Question 40

Encephalitis

Answer 40

- Inflammation of the brain - Headache, confusion, seizures, hallucinations - Can be fatal - Enterovirus, HSV, rabies, arboviruses

Question 41

Acute flaccid paralysis

Answer 41

- acute onset of flaccid paralysis in one or more limbs - Caused by anterior horn cell infection with wild or vaccine polio virus

Question 42

What can primary HIV disease lead to

Answer 42

- AIDS Dementia complex (brain) - Vacuolar Myelopathy (spinal cord) - Peripheral Neuropathy (nerve) - Meningitis (acute or chronic)

Question 43

Zika virus

Answer 43

- Spread by mosquitos - Most cases asymptomatic, mild flu like symptoms - Increased risk of Guillain-Barré Syndrome - Vertical transmission causing microcephaly and other congenital brain abnormalities - Sexual transmission and blood-transfusion (WHO)

Question 44

Reproduction number (R0)

Answer 44

- The average number of secondary cases generated by one primary case in a susceptible community - The higher the R0, more persons infected from one primary case

Question 45

Viral shedding

Answer 45

- Viruses shed from an infected host can infect new susceptible hosts - May be shed from primary site of multiplication or from target organ - Healthy individuals may shed viruses continuously (e.g. HSV in saliva)