Red Viral Rashes Flashcards
Vesicle lesion defn
blister, fluid filled, <1cm
Bulla defn
blister >1cm
Macule defn
Slightly raised reddened skin rash, <1cm
Pustule defn
pus filled blister deep under skin, painful, <1cm
Viruses that cause red macular rashes
Measles, Rubella, B19, HHV6,7
Viral serology - what are you looking for?
Look for convalescent increase in AB - must be 4 fold (ie 1/2 to 1/32 dilution). Take before and then after (ie two weeks apart)
Measles virus descriptions
Rubeola. -ssRNA. Only one serotype, only in humans. Not latent or persistent. Two surface glycoproteins (H and F), M protein under envelope
Classic measles symptoms
Fever, malaise, anorexia, conjunctivitis, photophobia, myalgia. Koplik’s spots (appear on buccal mucosa: gray or other spots diagnostic of measles prior to rash). Characteristic rash. Intense inflammation of lymphoid tissue and mucosa of the respiratory tract. Tracheobronchitis and pneumonia common
What is the characteristic rash progression of measles?
Maculopapular rash, behind ears, then face, upper arms and trunk, then legs by 3rd day.
Gestational Measles
risk of pneumonia during the 3rd trimester. No fetal abnormality but premature delivery and spontaneous abortion
Congenital measles
Rash present at birth or in first 10 days. Mortality 30%
Measles in the immunosuppressed
Severe, frequently fatal often no rash (b/c no immune system!). Giant cell pneumonia (syncytia). Sub-acute encephalitis: mortality >85%
Pathogenesis of measles
Cellular receptor is CD46 (C3b binding protein on many cells). Infection of vascular endothelial cells causes increased permeability and edema. Formation of multi-nucleated cells (F protein), syncytia with inclusion bodies in host cells – results in host cell death (necrosis), can lead to more bacterial infections
Measles causes immunosuppression
Lasts several weeks after rash. Virus infects Dendritic cells and monocytes. Circulating T cells decreased. Cytokine response is thrown off so you increase TH2 more when you need TH1, less macrophage activity
Immunity to measles
Generally good for life afterwards. ABs last for life.
Incubation period and infectiousness of measles
8-12 days incubation. Airborne transmission.
Susceptibility to measles
Male, pregnant or malnourished. Much more lethal in developing countries.
Complications of measles
Otitis media, pneumonia, diarrhea, encephalitis most common. Keratitis in kids with vit A deficiency (corneal ulceration and blindness). Secondary bacterial infections. Acute post-infectious encephalitis is the most common neurological complication of measles. SSPE: sub-acute sclerosing panencephalitis – rare delayed complication, presents 6-8 years after, fatal in 1-3 years)
Tx and prevention of measles
Isolate cases to prevent spread. Tx is symptomatic: bed rest, hydration, antipyretics, vitamin A. No good antiviral. Passive immunoprophylaxis with Ig for contacts is doable. Vaccination is key!
Measles vaccine
95% effective. Combined measles, mumps, rubella and varicella vaccine (MMRV): First dose at 12-15 mo, Second dose at 4-6
Rubella virus description
aka German measles. Enveloped virus. 1 serotype, human only. E1 (hemagglutinin), E2 glycoproteins. Concern is over effects on fetus.
Rubella symptoms in children/teens
Usually rash with no warning in kids. Adults and adolescents 1-5 days prodrome. Lymphadenopathy, conjunctivitis, other classic symptoms. Erythematous maculopapular rash appears after 16 days, first on face then spreads to trunk and extremities. Rash lasts 3 days
Congenital rubella
Severe effects on child. 80% deafness. If mother is infected it is very likely. The earlier in pregnancy the worse the defects
Transmission of rubella
Droplet and vertical. Shed lots after 10-18 days
Tx and diagnosis for rubella
Clinical. no antiviral.
B-19 virus characteristics
Parvovirus. aka “slapped cheek syndrome/erythema infectiosum/5th disease”. Non enveloped ssDNA virus. only in humans. Common in kids, but usually ok. Tropism for erythrocytic precursors. No vaccine
Pregnancy and B-19
High risk of spontaneous abortion.
B-19 transmission
can be transmitted vertically from mother to fetus, or by the respiratory routes and by transfusions. Possibly direct contact or droplet
Disease caused by B-19
Usually asymptomatic. Mild rash on face, trunk.
Transient aplastic crisis
Caused by B-19. Lytic infection of RBC precursors, temporary shutdown of RBC production. Can cause anemia, most serious in fetus.
B-19 pathogenesis
B-19 requires actively dividing cells (needs cellular functions expressed only during S phase). B19 attaches to host cells by means of the P antigen.
B-19 development
Fever for 5-7 days, rash 15-17 days.
HHV-6,7 - pathogenesis and name of disease
Replicates in CD4+ cells, NK cells. Causes roseola aka exanthema subitum in infancy
HHV-6,7 - progress of disease
Abrupt high fever (to 40°C) lasting 2-3 days. Drop in temperature coincides with rash. Rash lasts 1-2 days. Drowsiness, irritability. Rash first on neck, behind ears and back, then spreads to scalp and torso. 2-7 days illness
