Exam 1: Viral Exanthums

Question 1

Exanthums

Answer 1

Disease manifestations on the external surface of the body.

Question 2

Skin Lesions

Answer 2

Question 3

Childhood

Viral Exanthums

Answer 3

1. Fifth disease
2. Rubella
3. Roseola
4. Measels
5. Chickenpox

Question 4

Fifth Disease
Overview

Answer 4

“Erythema Infectiosum”

• Caused by Parvovirus B19
  
  • Very small naked virus
  • ssDNA ⇒ both ⊕ and ⊖
  • Replicates within the nucleus
• Targets mitotically active erythroid precursor cells
• Cytolytic
• Blocks erythroid production for ~ 1 week

Question 5

Fifth Disease

Transmission & Epidemiology

Answer 5

• Parentaral transmission
  
  • Spread by respiratory droplets
  • Age group ⇒ 4-15 year olds
  • Late winter and spring
• Vertical transmission from mother to fetus

Question 6

Fifth Disease

Pathogenesis

Answer 6

Biphasic Course:

1. Initial phase
   
   • Colonizes nasopharnx or URT
   • Incubation period ~ 1 week
     
     • Prodromal flu-like sx with low-grade fever
     • Infectious
   • Erythrocyte production is blocked for ~ 1 week
   • Phase stopped by Ab
2. Secondary phase
   
   • Immune complex mediated
   • Rash
     
     • Starts on cheeks ⇒ slapped cheek
     • Spreads to downward ⇒ lacy rash
     • Resolves in 1-2 weeks
   • Adults can develop:
     
     • Arthralgias
     • Arthritis
     • Edema
   • Not infectious
   • Seronegative pregnant women at risk for fetal loss

Question 7

Fifth Disease

Diagnosis & Treatment

Answer 7

• Diagnosis
  
  • Clinical dx
    
    • Slapped cheek rash
    • Lacey rash on body
  • Serological testing
    
    • Parvovirus B19 IgM and IgG
      
      • Differentiate from Rubella rash
    • For pregant women with ⊕ contact
• Treatment
  
  • None
  • Self-limiting in immunocompetent children

Question 8

Fifth Disease

Complications

Answer 8

• Seronegative pregnant woman
  
  • Risk for fetal death from hydrops fetalis
  • Survive ⇒ fetal anemia
    
    • In utero transfusions have been done
  • No congenital abnormalities
• Hosts with sickle cell disease
  
  • Risk for reticulocytopenia
  • Aplastic crisis
• Immunosuppressed hosts
  
  • Progressive bone marrow suppression
  • Chronic disease

Question 9

Rubella

Overview

Answer 9

“Little red or German measles”

• Caused by Rubella virus
  
  • ss ⊕-sense RNA enveloped virus
  • Replicates in the cytoplasm & buds
  • A Togavirus but not transmitted by arthropod vector
  • Only 1 serotype
• Congenital infection ⇒ can be acquired during pregnancy from the mother

Question 10

Rubella

Transmission

Answer 10

• Spread by respiratory droplets
  
  • Infectious during ~18 day incubation period
  • Continued shedding from pharynx for 1-2 weeks post disease
• Vertical transmission
  
  • Seronegative mother to fetus
  • During first 20 weeks of pregnancy

Question 11

Rubella

Epidemiology

Answer 11

• Human reservoir ⇒ only host
• One serotype
• Late winter/early spring
• Outbreaks every 6-9 years

Question 12

Rubella

Pathogenesis

Answer 12

Postnatal infections:

• Colonization in URT
  
  • Replicates in lymphoid tissue
  • Prodromal phase ⇒ 1-2 weeks
    
    • Local lymphadenopathy & flu-like sx
• Primary viremia
  
  • Disseminates throughout body
• Also spreads via mononuclear phagocyte system
  
  • Generalized lymphadenopathy
• Secondary viremia
  
  • Erythematous maculopapular rash and arthralgia
    
    • Likely immune complex mediated
    • Lasts < 3 days
  • Transplacental transmission during this time

Question 13

Rubella

Clinical Manifestations

Answer 13

• Children
  
  • 20-50% asymptomatic
  • Lymphadenopathy, fever
  • 3 day maculopapular rash
• Adults
  
  • Arthralgia
  • Arthritis
• Complications
  
  • Rarely thrombocytopenia or encephalopathy

Question 14

Congenital Rubella Syndrome

(CRS)

Answer 14

• Vertical transmission from seronegative mother ⇒ fetus
  
  • Colonizes the placenta
  • Disseminates and replicates in many fetal tissues
• Minimally cytolytic
  
  • Affects growth, mitosis, chromosomes
• Congenital defects
  
  • > 50% during 1st month of gestation
  • 20-30% during 2nd month
  • 5% during 4th or 5th month
• Common anomalies
  
  • Growth retardation
  • Ophthalmologic
  • Cardiac
  • Auditory
  • Neurologic
• Infants shed virus
  
  • From nasopharynx for up to 6 months
  • From urine for up to 1 year

Question 15

Rubella

Fetal Damage Mechanisms

Answer 15

1. Interference with normal development
2. Inflammatory response to microbial Ag
3. Placental insufficiency
   
   • Low birth weight
   • Premature birth
   • Fetal death

Question 16

Rubella

Diagnosis

Answer 16

• In congenitally infected infants
  
  • Virus isolated from nasal specimens, blood, urine and CSF
    
    • PCR from urine
  • Serology
    
    • Rubella IgM presence suggestive
    • 4x increase of Rubella IgG in convalescent sample confirms
• Many states have implemented prenatal screening of pregnant women

Question 17

Rubella

Immunity

Answer 17

• Ab develops after 1st viremia
• Rash due to Ab/Ag complexes in skin
• Cell-mediated immunity resolves infection
• Natural infection leads to life-long sterilizing immunity
  
  • Ab blocks viremia
  • Can still shed virus from URT

Question 18

Rubella

Prevention

Answer 18

MMR vaccine

• Live attenuated virus
• Contraindicated for nonimmune pregnant women
• Primary purpose to prevent CRS

Question 19

Roseola

Overview

Answer 19

“Exanthum subitum”

• Caused by Herpesvirus 6 and 7
  
  • Large enveloped dsDNA virus
  • Transcription & translation coordinated in 3 phases
    
    • Immediate early proteins ⇒ DNA binding proteins
    • Early proteins ⇒ DNA pol, transcription factors
    • Late proteins ⇒ structural proteins
• Causes lytic, persistent, and latent infections
• Cell-mediated immunity important for control

Question 20

Roseola

Transmission and Epidemiology

Answer 20

• Transmission
  
  • Spread via saliva & respiratory droplets
  • Primary infection occurs in early childhood
    
    • Most people seropositive by age 4
• Epidemiology
  
  • Common in winter & early spring

Question 21

Roseola

Pathogenesis

Answer 21

• Acute infection ⇒ 6mo-2yr
  
  • 4-7 day incubation
  • High fever of 103-106 °F for 4 days
    
    • Febrile seizures
  • Diffuse lacy rash for 1-2 days
    
    • Develops as fever ends
    • Usually spares the face
  • Virus replicates in helper T-cells
    
    • Can lead to immunocompromise
  • Resolution with no complications
• Latency
  
  • Can remain in T-cells and monocytes
• Reactivation
  
  • May occur with immunosuppresion
  • Periodically found in saliva of most adults

Question 22

Roseola

Diagosis and Treatment

Answer 22

• Diagnosed clinically
• No treatment ⇒ provide supportive care
• No vaccinations