Micro-Pox/Parvo Viruses Flashcards
Parvovirus structure
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
Is parvovirus seropositivity common in the population?
Yes, ~ 50% by school age
Parvovirus causes this disorder in kids
Erythema infectiosum
Erythema infectiosum is caused by which parvovirus
B19
How is parvovirus B19 spread?
direct contact with secretions which occurs BEFORE rash appears!
Erythema infectious characteristics
‘Slapped cheek’ + lacy rash on trunk/limbs
Adults flu-like > rash
Kids more rash
Describe the biphasic infectious cycle of parvo B19
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
Generally speaking, which populations get parvovirus infections?
Kids - erythema infectiosum
SSD - aplastic crisis
Immunocompromised - chronic anemia
Pregnancy - severe fetal anemia and miscarriage
Explain B19 effect on SSD pts
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
Explain B19 effect on immunocompromised
RBC precursor lysis goes on and on leading to anemia
Explain B19 effect on pregnant ladies
Transplacental
Minority of infections cause severe fetal anemia, hydrops fetalis
More common during 1st half of prego
How is B19 diagnosed?
Rash appearance
How is B19 treated?
Supportive - flu-like/rash
Transfusion for anemia
No vaccine
B19 is often confused with __
rubella
What other four viruses commonly cause childhood rashes?
Chicken pox
Measles
Rubella
Roseola
Which other viruses pose a problem for pregnant moms (that cause rash?)
Rubella and measles
The pox virus is in the genus __ and molluscum contagiosium is in the genus __
orthopox; unclassified
Describe the structure of the poxviridae
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
Where do poxviruses replicate?
CYTOPLASM ALL DAY LONG even though DNA
Explain poxvirus replication cycle
- Uncoating: virus enters and releases core particle
- Core particle contains DNA-dep RNA pol, capping and methylating enzymes, and polyA polymerase
- Early mRNA synth occurs in core then mRNA travels to cytoplasm for translation
- Uncoating II: DNA released into cytoplasm and replication begins
- Late transcripts and proteins prod in cyto lead to virus assembly
- Most virions remain IC; membrane is de novo, ‘crescents’ envelope the core structures; 1% get 2nd mem from Golgi and are released
- EEV - extracellular enveloped virus - infectious agents
Forms of smallpox and fatality?
Major - 25%
Minor - 1%
What are some ways to distinguish smallpox from chicken pox?
All pustules at same stage (not true for chicken)
Pustules have little dimple in middle
Smallpox has febrile prodrome
When is smallpox no longer contagious?
When ALL pustules are gone
What is the cause of death in smallpox?
Toxic effects to vascular endothelium
Molluscum contagiosum childhood form
Lesions on face, trunk, limbs
Spreads by skin contact!
Tropical
Molluscum contagiosum young adult form
STD
Lower abdomen lesions
Molluscum contagiosum dx?
Appearance, confirmed by cytoplasmic inclusions in eosinophils
How long to molluscum contagiosum lesions stay?
2-12 mo
Smallpox disease progression
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)
Vaccinia vaccine characteristics and timing
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
Four contributing factors to smallpox vaccine success
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
Vaccinia contraindications
prego/breast feed, immunocomp, eczema, severe acne, etc, under 18, heart disease
Vaccinia complications
Severe adverse reaction > life-threatening complications* > death
*Progressive vaccinia > encephalitis > eczema-shock > MI
How to reverse vaccinia reaction?
VIg - vaccinia immunoglobulin, and potentially cidofovir
