Enteroviruses

Question 1

Features of enteroviruses

Answer 1

1. Picornavirus - small, non-enveloped, ssRNA (+)
2. Stable - insensitive to detergents, survive for months at 4C, survive exposure to 60C
3. Replicate in GIT
4. Prefers warm, moist environment - common in tropics, epidemic in summer months

Question 2

Examples of enteroviruses

Answer 2

1. Poliovirus
2. Coxsackie virus A & B
3. Echovirus - Enteric Cytopathic Human Orphan

Question 3

Classification of enteroviruses

Answer 3

• recently reclassified based on molecular properties
• Enterovirus A-D
• newly discovered viruses - enterovirus xx
• > 60 different serotypes
• important new enteroviruses: EV70 - Acute Haemorrhagic Conjunctivitis; EV71 - Encephalitis, HFMD; EV72 - Hep A virus - reclassified as hepatovirus

Question 4

Features of HFMD

Answer 4

• common, mild childhood infection

- caused by several different serotypes of enteroviruses - CA16, CA24, EV71

Question 5

Features of EV71

Answer 5

• infection manifests as childhood exanthem (rash); HFMD indistinguishable from CA16
• small proportion results in CNS infection
• common, highest seroconversion rate in children aged 2-5, slows down after
• neutralising Ab titre reduces with age - low reinfection rate
• vaccination in early phase clinical trials

Question 6

Incubation period of poliovirus

Answer 6

7-14 days

Question 7

Pathophysiology of poliovirus

Answer 7

1. Primary site of infection: lymphoid tissue assoc w oropharynx & gut (GALT)
2. Virus production - transient viraemia, may infect CNS
3. Replication in grey matter - esp motor neurones in anterior horns of spinal cord & brainstem - produces distinctive ‘plaques’ due to lytic replication of the virus & probably inflamm caused by an over-enthusiastic immune response

Question 8

Symptoms of poliovirus

Answer 8

1. 90-95% subclinical/asymptomatic
2. 4-8% abortive/mild infection - minor influenza-like illness, recovery within a few days, may have aseptic meningitis
3. 1-2% major illness - when it gets into CNS
   - commonly aseptic meningitis
   - involvement of ant horn cells - LMN - flaccid paralysis - causes muscle atrophy, releasing muscle tension on bone (bone growth depends on muscle tone) - affected limb will be shorter
   - involvement of medulla - resp paralysis & death (bulbar poliomyelitis)

Question 9

Treatment of poliovirus

Answer 9

Vaccination

1. IM poliovirus vaccine (IPV)
   - consists of formalin inactivated virus of all 3 poliovirus serotypes
2. Oral poliovirus vaccine (OPV)
   - consists of live attenuated virus of all 3 serotypes, serial passage in pri monkey kidney cells

can be eradicated!!

• cheap vaccine
• cannot survive long out of the body

Question 10

Comparison of poliovirus vaccines

Answer 10

• IPV is IM, req trained personnel vs OPV - PO
• IPV confers immunity but still acts as carrier vs OPV lifelong immunity, prevents carriage
• IPV no risk of vaccine associated paralysis vs OPV small risk of VAP (regain virulence, reversion to wild type)
• IPV vaccinates patients only

Question 11

Features of coxsackie & echoviruses

Answer 11

• Coxsackie A: mainly epithelial infections - herpangina, HFMD (CA16), conjunctivitis, encephalitis
• Coxsackie B: mainly muscular infections - Bornholm’s disease, myocarditis, encephalitis
• Echovirus: 30 serotypes, wide range of disease spectrum

Question 12

Diagnosis of coxsackie & echoviruses (3)

Answer 12

1. Virus isolation - cell culture from throat swabs, faeces, rectal swabs, CSF
2. Serology - rarely used due to cross reactivity, useful for sero-epidemiological studies
3. Molecular - RT-PCR, genetic seq for typing

Question 13

Treatment of coxsackie & echoviruses

Answer 13

1. No specific vaccine, some use IVIG to treat neonatal infections/severe infections in immunocompromised but efficacy is uncertain
2. Some susceptible agains Pleconaril