L49: Medically Important Viruses

Question 1

Picornavirus (big family)

Answer 1

1. Enterovirus:
   - Rhinovirus (Respiratory route, URT infection)
   - Enterovirus (GI/faecal-oral route, systemic infection e.g. poliovirus)
2. Paraechovirus
3. Hepatovirus

Question 2

Pathogenesis of Enterovirus

Answer 2

• no lipid envelope
• Stability in environment: can survive external environment, gastric acidity and faecal enzyme
• Asymptomatic infection (Iceberg effect): multiply in intestinal lymphoid tissue, remain undetected and can still transmit from asymptomatic persons
• Flu-like illness: viraemia —> fever
• Full disease syndrome: organ dysfunction: poliomyelitis, meningitis, encephalitis, myocarditis
• DO NOT cause diarrhoea
• Once recover immunity is lifelong, no mechanisms for persistence

Question 3

Enterovirus 71

Answer 3

Hand,foot and mouth disease

Question 4

Polio vaccine

Answer 4

Type 1, 2, 3 (type 2 + 3 now eradicated)

Multivalent (Type 1, 2, 3)

1. Oral live attenuated (one live virus each time, at least 3 doses)
   - easy to administer, mucosal immunity —> block transmission
   - virulence reversion
   - now type 2 oral vaccine removed —> IPV only
2. Killed (3 dose: primary, secondary and booster)

Question 5

Pathogenesis of Herpesviridae

Answer 5

• double stranded DNA virus
• Enveloped
• Virus latency (within any level of spinal cord): Once infected —> always infected
• Viral genome: integrated / episomal
• Genome not completely expressed
• Viral antigens not visible on cell surface: evade host immune mechanism
• Trigger from latency to full replication (from time to time): Lysogenic cycle —> Lytic cycle —> can spread to others

Question 6

Herpes simplex type 1 vs Herpes simplex type 2

Answer 6

HSV1 (above waist)

• Often asymptomatic
• Mild oral lesions to severe stomatitis
• Herpetic whitlow
• macule vs papule
• vesicle vs pustule
• ulcer

HSV2 (below waist)
- genital herpes

Question 7

Primary infection and recurrence of HSV and VZV

Answer 7

Primary
HSV: mild pharyngitis, fever, genital herpes
VZV: chickenpox

Recurrence (depends on latency in which level of spinal cord)
HSV: cold sore, genital herpes
VZV: shingles / herpes zoster

Question 8

Pathogenesis of Influenza virus

Answer 8

• Type A, B, C
• RNA virus (single stranded, negative sense)
• segmented genome
• Haemagglutinin H1-H16: bind to sialic acid on host cells
• Neuraminidase N1-N9: cleaves Terminal sialic acid —> virus release
• Antigenic drift and Antigenic shift

Question 9

Antiviral drugs (4 classes)

Answer 9

1. Amantadine/ Rimantadine: Block virus uncoating
2. Oseltamivir, Zanamivir: Neuraminidase inhibitor
3. Baloxavir marboxil: cap-dependent endonuclease inhibitor (interfere with replication process)
   (4. Favipiravir: polymerase inhibitor)

Question 10

Symptoms of flu

Answer 10

Often caused by cytokines by host immune system (not the virus going to different body parts)

Question 11

Host immunity

Answer 11

• Cell-mediated response: helps recovery

- Humoral response: Antibody bind to Neuraminidase and Haemaglutinin —> neutralises infectivity

Question 12

Antigenic Drift vs Antigenic Shift

Answer 12

Drift: Minor antigenic change from MUTATION since RNA polymerase lack proof reading mechanism

Shift: Complete change of H and N antigen due to GENETIC REASSORTMENT: mixing of 2 viral genes (human and animals)

Question 13

Prevention of influenza

Answer 13

1. Vaccine: need to identify new antigenic drift variants
2. Antiviral: Oseltamivir / Zanamivir (Amantadine / Rimantadine not used anymore)
3. Hygiene