Picornavirus

Question 1

Picornaviruses - PERCH

Answer 1

Poliovirus
Echovirus
Rhinovirus
Coxsackievirus
HAV

Question 2

Structure of Picornavirus

Answer 2

Non-enveloped

+ stranded ssRNA, linear

All are enteroviruses (fecal-oral spread) except for Rhinovirus, which is acid labile

Question 3

Polio vaccine (Sabin)

Answer 3

Oral, live-attenuated vaccine - trivalent vs. serotypes 1, 2, and 3

Induces mucosal immunity (IgA) as well as systemic (IgG/IgM)

1 / 2.5 million associated with Vaccine-Associated Paralytic Polio (VAPP)

Not used in the US; contraindicated for immunocompromised patients

Question 4

Polio vaccine (Salk)

Answer 4

Injectable, inactivated, trivalent vaccine effective vs. serotypes 1, 2, and 3; exclusive use in US with 3 doses at ages 2, 4, and 12 months

Induces systemic IgG / IgM response; poor mucosal (IgA) response

Absence of live virus precludes possibility of reversion; can be given to immunocompromised patients

Question 5

HAV Vaccine

Answer 5

Oral, live/attenuated vaccine

Induces mucosal immunity (IgA) as well as systemic (IgG / IgM)

1 / 2.5 million result in Vaccine-Associated Paralystic Polio (VAPP) via reversion

Not used in US; contraindicated in immunocompromised

Question 6

Hand, Foot, and Mouth Disease

Answer 6

Caused by Coxsackie A infection

Presents in young children with fever, anorexia, malaise, sore throat, and vesicles on hands and feet; self-limiting

Question 7

Diseases associated with Enterovirus infection

Answer 7

Asceptic meningitis
Myocarditis (esp. Coxsackie B - dilated cardiomyopathy)
Hemorrhagic conjunctivitis
Acute flaccid myelitis (Enterovirus D68)
Non-specific fever / rash (esp. in summer months)

Question 8

Poliovirus - Pathogenesis

Answer 8

Infection occurs via ingestion of contaminated food or water; primary replication occurs in the pharynx, small intestine, and lymphatic tissue; primary viremia seeds infection to skeletal muscle where secondary replication occurs

CNS infection occurs via secondary viremia across the BBB or via retrograde axonal transport of virus up skeletal motor neurons

Causes destruction of motor neurons in the anterior horn of the spinal cord

Question 9

Poliovirus - Presentation

Answer 9

90-95% asymptomatic / inapparent

5% minor URI

1-2% asceptic meningitis

0.1% flaccid paralysis

Question 10

What was the WHOs original goal for eradication of polio?

Answer 10

Goal set in 1988 to eradicate polio by 2000

Question 11

Polio eradication strategy

Answer 11

1. Routine immunization with OPV
2. Additional doses of OPV during National Immunization Days
3. Acute flaccid paralysis surveillance
4. Polio-free certification after 2-3 years without detection of circulating WT virus
5. Laboratory containment of OPV and WT strains
6. Stop OPV 3 years after certification

Question 12

National Immunization Days

Answer 12

Immunization of every child < 5 years with 2 doses OPV regardless of prior vaccination status

Catches kids who haven’t been vaccinated and boosts immunity in prior vaccinees

Question 13

How is surveillance of AFP performed?

Answer 13

Isolation and culture of virus from stool sample of affected patient; culture must grow cytopathic strain

Ab or ELISA assay of virus isolated from cytopathic culture to determine serotype

PCR distinguishes OPV vs. WT strain

Question 14

Current status of polio eradication

Answer 14

2012: 222 global cases reported

WT OPV-2 and OPV-3 have been eradicated

Goal to end vaccination - 2019