Lecture 1: Measles, Rubella, & Roseola

Measles Virus

Enveloped, negative-sense ssRNA virus

Measles Clinical Manifestations

Phase 1: Prodrome

Enanthem: Koplik’s spots on buccal mucosa

Coryza, persistent cough, conjunctivitis

High fever

Phase 2: Exanthem

Erythematous, maculopapular rash begins behind the ears and spreads toward the feet

Phase 3: Resolution

Rise in antibody titers and rash fades in the same order that it appeared, leading to life-long immunity

Acute encephalitis + death

Subacute sclerosing panencephalitis (SSPE) - fatal degenerative disease of the CNS— develops 7 to 10 years after infection

Measles Vaccine

Live Attenuated vaccine

Introduction of the Measles vaccine reduced childhood infectious disease mortality by ~30-50%

1st dose: 12-15 months of age

2nd dose: 4-6 years

Bonus dose for infants (6-11 mo.) traveling to endemic areas

Post-exposure within 72 hours

Maternal IgG against measles can neutralize live-attenuated vaccine virus before it infects target cells → reduce antigenic stimulation of B cells

Measles triggers

Immune Amnesia

Measles virus results in viremia and lymphopenia

Measles preferentially infects CD150-expressing memory lymphocytes → apoptosis

Immune system “forgets’ prior infections or vaccinations

Decrease in both naïve and memory B cell diversity that persisted

Measles Passive Immunization

Post exposure within 6 days: Immune globulin

Rubella

Enveloped, non-segmented, positive-sense RNA virus

Rubella Clinical Manifestations

Phase 1: incubation period

Phase 2: Prodrome:

Low grade fever

Headache, malaise, cough, conjunctivitis, coryza, Lymphadenopathy

Enanthem: Forchheimer spots on soft palate

Phase 3: Exanthem: Top-down rash-macular or maculopapular rash appears 1-5 days later

Congenital Rubella Syndrome (CRS)

Viremia during maternal infection leads to fetal infection via placenta and interferes with fetal organogenesis

Restricted development of precursor cells by the virus

Miscarriage & Stillbirth

Low birth weight

"Blueberry muffin" skin lesions

Heart defects

Eye defects

Hearing loss & CNS involvement

Learning disabilities

Rubella infection poses the highest risk to the fetus during the first month of pregnancy

Continues to occur in unvaccinated pregnant women with travel history

Vaccinate at least 28 days prior to pregnancy

Diagnosis of Primary Rubella

Serological detection of anti-rubella IgM by enzyme immunoassay - detectable 4 days post-rash onset

4X increase in Rubella-specific IgG

Diagnosis of CRS

Detection of IgM within the first six months after birth

Detection of Rubella RNA in amniotic fluid or fetal blood (RT-PCR)

Rubella Vaccine

Live attenuated vaccines: Meruvax II (as part of MMR)

Two doses: 12-15 mo, 4-6 yr

Contraindications: pregnancy, immunocompromised, & history of anaphylaxis to neomycin

Roseola

Caused by infection with Human Herpesvirus -6 or -7

Enveloped, linear dsDNA viruses that establish life-long infections

Roseola Clinical Manifestations

Phase 1:incubation period

Biphasic disease:

Phase 2: Acute onset of high fever (over 103 ̊F) and lasts 3-7 days - most contagious phase.

Phase 3: 12-24 hours after fever breaks, a rose-colored rash appears that lasts 1-3 days

Enanthem: Nagayama spots: Reddish macules and papules on the soft palate and uvula in subset of patients

Exanthem of maculopapular rash starts on the trunk, then spreads to the neck and extremities

Cough, runny nose, sore throat

Vomiting, diarrhea, anorexia

Pink eye

Lymphadenopathy

Febrile seizures triggered by a rapid spike in fever