Viruses Causing Exanthums

Question 1

Measles

General Characteristics

Answer 1

• Caused by Rubeola virus
• Belongs to the family Paramyxovirus
• Single-stranded ⊖ sense RNA virus
• Enveloped
• Only one antigenic type
• Humans are the only reservoir

Question 2

Rubeola Virus

Structural Proteins

Answer 2

• Hemagglutinin (H) ⇒ important in viral attachment
• Fusion factor (F) ⇒ fusion of cells and viral entry
• Matrix protein (M) ⇒ located inside viral envelope, important in assembly of virion

Question 3

Rubeola Virus

Transmission/Epidemiology

Answer 3

• Respiratory droplet transmission
• Highly contagious and very virulent
  
  • 90% attack rate
  • 100% symptomatic ⇒ everyone gets disease, no latent infections
• Contagious from 1-2 days before onset of symptoms up to 4 days after onset of rash
• Peak incidence: Winter & Spring

Question 4

Rubeola Virus

Pathogenesis

Answer 4

• Incubation period 7-21 days
• Virus initially replicates locally in the respiratory epithelium
• Spreads through the lymphatics ⇒ liver, spleen and lymph nodes
• Period of replication there ⇒ primary viremia ⇒ conjunctiva, respiratory tract, urinary tract, secondary lymphoid organs, CNS
• Second viremia ⇒ endothelial cells in vessels
• Immune response to virus infected endothelial cells ⇒ maculopapular rash (DTH)
• Virus induces syncytia formation and multinucleate giant cells
  
  • Causes pathology
  • Hides from the immune response

Question 5

Measles

Histology

Answer 5

Virus induces syncytia formation and multinucleate giant cells.

Question 6

Measles

Clinical Manifestations

Answer 6

• Begins with cough, coryza, conjunctivitis, high fever
• Koplik’s spots ⇒ characteristic spots on buccal mucosa
  
  • Appears first day or two of the infection
  • Frequently disappears when maculopapular rash develops
• Characterized by maculopapular rash
  
  • Lasts ~ 5 days
  • Caused by T-cells targeted to infected endothelia cell lining vessels
• Child is usually very sick

Question 7

Measles

Complications

Answer 7

• Bacterial superinfection (respiratory infections)
  
  • Measles infection is immunosuppressive
  • Allows fulminant superinfections
• Post-infectious meningo-encephalitis
  
  • May occur 5-7 days after rash
  • Caused by the immune system reacting to virus in brain
  • Mortality 10-20%
  • Retardation 65%
• Subacute sclerosing panencephalitis (SSPE)
  
  • Progressive degenerative disease of CNS
  • Caused by defective measles virus assembly during infection
  • Occurs 2-10 years after primary measles infection
  • Usually fatal
• Progressive infectious encephalitis
  
  • Occurs in pts with defective CMI
  • Usually fatal
• Immunocompromised (T-cell deficient)
• Giant cell pneumonia with no rash

Question 8

Measles

Immunity, Treatment, and Prevention

Answer 8

• CMI in response to virus resolves disease
• Responsible for life long immunity
• Live attenuated measles vaccine (MMR)
  
  • Given at 12-15 mo
  • One boost given during elementary school
• IGIV can provide transient protection for exposed immunocompromised children
• No specific antiviral therapy

Question 9

Roseola

Overview

Answer 9

“Exanthum subitem”

• Caused by Human Herpesvirus-6
  
  • Herpesviridae family
  • Subtype: Beta-herpesviruses
  • Large dsDNA virus, enveloped
• Transcription and translation coordinated and regulated:
  
  • Immediate early proteins ⇒ DNA binding proteins
  • Early proteins ⇒ DNA pol, transcription factors
  • Late proteins ⇒ structural proteins

Question 10

Roseola

Transmission/Epidemiology

Answer 10

• Spread via saliva and respiratory aerosols
• Common in young children
• Most are seropositive by age 4
• Frequent cause of ER visits in young children d/t febrile seizures

Question 11

Roseola

Pathogenesis/Clinical

Answer 11

• 4-7 day incubation
• High fever for 3-5 days
• Rash for 1-2 days, due to T-cell response
  
  • Virus replicates in T-cells
  • Recovery with no complications
• Virus remains latent (probably in T-cells)
• Reactivation may occur with immunosuppression
  
  • Virus seen in AIDS pts
  • May contribute to pathogenesis of AIDS
  • Also contributes to transplant graft rejection

Question 12

Roseola

Management

Answer 12

Dx: clinical

Treatment/Prevention: none

Question 13

Erythema Infectiosum

Overview

Answer 13

“Fifth Disease”

• Caused by Parvovirus B19
• Small naked linear ssDNA virus
• Icosahedral capsid
• Extremely resistant to physical inactivation

Question 14

Erythema Infectiosum

Transmission/Epidemiology

Answer 14

• Respiratory secretions
• Parenteral transmission
• Age group 4-15 y/o
• Late winter and spring

Question 15

Erythema Infectiosum

Pathogenesis/Clinical

Answer 15

• Initially replicates in nasopharynx or URT
• 1st viremia to the bone marrow
• Replicates in mitotically active cells of erythroid origin
• 2nd viremia ⇒ viruses may cross placenta
• Biphasic disease
  
  • 1st phase ⇒ flu-like symptoms
    
    • Infectious period
    • Stopped by antibody
  • 2nd phase (symptomatic) ⇒ “slapped cheek” rash and arthralgia
    
    • Caused by immune complexes
• Individuals with chronic anemia (sickle cell) at risk for aplastic crisis
• Seronegative pregnant women at risk for fetal loss

Question 16

Erythema Infectiosum

Management

Answer 16

• Clinical dx ⇒ slapped cheek rash, lacey rash on body
• Parvo B19 IgM and IgG can be detected
• Evaluation of exposed pregnant woman
• Should be differentiated from rubella rash
• Treatment/Prevention – none