Micro-Pox/Parvo Viruses

Question 1

Parvovirus structure

Answer 1

1:1 +/- ssDNA linear small icosahedral unenveloped that replicates in the nucleus of RAPIDLY DIVIDING cells

Dividing req’d bc need access to host DNA pol

Question 2

Is parvovirus seropositivity common in the population?

Answer 2

Yes, ~ 50% by school age

Question 3

Parvovirus causes this disorder in kids

Answer 3

Erythema infectiosum

Question 4

Erythema infectiosum is caused by which parvovirus

Answer 4

B19

Question 5

How is parvovirus B19 spread?

Answer 5

direct contact with secretions which occurs BEFORE rash appears!

Question 6

Erythema infectious characteristics

Answer 6

‘Slapped cheek’ + lacy rash on trunk/limbs

Adults flu-like > rash
Kids more rash

Question 7

Describe the biphasic infectious cycle of parvo B19

Answer 7

Lytic phase

• Incubation 1 wk
• Next, viremia with dec Hgb levels
• Then flu-like S/S with virus in throat
• IgG antibody levels rise

Noninfectious immunologic phase

• By day 14-ish, virus difficult to isolate and rash appears (also arthralgia)
• Not contagious

Question 8

Generally speaking, which populations get parvovirus infections?

Answer 8

Kids - erythema infectiosum
SSD - aplastic crisis
Immunocompromised - chronic anemia
Pregnancy - severe fetal anemia and miscarriage

Question 9

Explain B19 effect on SSD pts

Answer 9

Lysis of erythroid precursor cells not tolerated well b/c already need rapid turnover; no RBC production during infection is devastating and causes severe anemia

Question 10

Explain B19 effect on immunocompromised

Answer 10

RBC precursor lysis goes on and on leading to anemia

Question 11

Explain B19 effect on pregnant ladies

Answer 11

Transplacental
Minority of infections cause severe fetal anemia, hydrops fetalis

More common during 1st half of prego

Question 12

How is B19 diagnosed?

Answer 12

Rash appearance

Question 13

How is B19 treated?

Answer 13

Supportive - flu-like/rash
Transfusion for anemia

No vaccine

Question 14

B19 is often confused with __

Answer 14

rubella

Question 15

What other four viruses commonly cause childhood rashes?

Answer 15

Chicken pox
Measles
Rubella
Roseola

Question 16

Which other viruses pose a problem for pregnant moms (that cause rash?)

Answer 16

Rubella and measles

Question 17

The pox virus is in the genus __ and molluscum contagiosium is in the genus __

Answer 17

orthopox; unclassified

Question 18

Describe the structure of the poxviridae

Answer 18

Complex-shaped, linear large dsDNA genome complexed with proteins visible under microscope

IC virus has core and lateral bodies which are surrounded by envelope, while EC virus has addit’l envelope

Question 19

Where do poxviruses replicate?

Answer 19

CYTOPLASM ALL DAY LONG even though DNA

Question 20

Explain poxvirus replication cycle

Answer 20

1. Uncoating: virus enters and releases core particle
2. Core particle contains DNA-dep RNA pol, capping and methylating enzymes, and polyA polymerase
3. Early mRNA synth occurs in core then mRNA travels to cytoplasm for translation
4. Uncoating II: DNA released into cytoplasm and replication begins
5. Late transcripts and proteins prod in cyto lead to virus assembly
6. Most virions remain IC; membrane is de novo, ‘crescents’ envelope the core structures; 1% get 2nd mem from Golgi and are released
7. EEV - extracellular enveloped virus - infectious agents

Question 21

Forms of smallpox and fatality?

Answer 21

Major - 25%

Minor - 1%

Question 22

What are some ways to distinguish smallpox from chicken pox?

Answer 22

All pustules at same stage (not true for chicken)
Pustules have little dimple in middle
Smallpox has febrile prodrome

Question 23

When is smallpox no longer contagious?

Answer 23

When ALL pustules are gone

Question 24

What is the cause of death in smallpox?

Answer 24

Toxic effects to vascular endothelium

Question 25

Molluscum contagiosum childhood form

Answer 25

Lesions on face, trunk, limbs
Spreads by skin contact!
Tropical

Question 26

Molluscum contagiosum young adult form

Answer 26

STD

Lower abdomen lesions

Question 27

Molluscum contagiosum dx?

Answer 27

Appearance, confirmed by cytoplasmic inclusions in eosinophils

Question 28

How long to molluscum contagiosum lesions stay?

Answer 28

2-12 mo

Question 29

Smallpox disease progression

Answer 29

Flu-like prodrome with high fever
Next, small red spots in mouth
Rupture - most contagious
Next, infected macros migrate to epidermis and cause lesions (toxemic phase)

Question 30

Vaccinia vaccine characteristics and timing

Answer 30

Live
Localized lesion disappear within 2 wks
3 days post-exp is protective, 7 days post-exp can lessen severity

Effectiveness drops at 3 yrs and gone at 20

Question 31

Four contributing factors to smallpox vaccine success

Answer 31

Humans as only reservoir
No healthy carriers (dead or immune)
No sub-clinical cases
Effective vaccine available

All 4 usually necessary for disease eradication through vaccination

Question 32

Vaccinia contraindications

Answer 32

prego/breast feed, immunocomp, eczema, severe acne, etc, under 18, heart disease

Question 33

Vaccinia complications

Answer 33

Severe adverse reaction > life-threatening complications* > death

*Progressive vaccinia > encephalitis > eczema-shock > MI

Question 34

How to reverse vaccinia reaction?

Answer 34

VIg - vaccinia immunoglobulin, and potentially cidofovir