MMR Flashcards
Measles
One of the most contagious diseases, rash covering arms and stomach
Measles Virus Characteristics
Paramyxovirus (genus: morbillivirus), negative strand non-segmented RNA virus, enveloped
Measles virus characteristics
Lipid envelope studded with viral glycoproteins (H+F)
Nucleocapsid
Viral RNA, N(nucleoprotein), P (phosphoprotein), L (large protein).
Genome of measles virus
6 Genes encoding 8 proteins, P gene encodes multiple proteins.
What proteins does P encode?
P- phosphoprotein required for polymerase activity
V- accessory protein that blocks the innate immune response
C- accessory protein that blocks the innate immune response
Measles attachment
H protein binds to CD46 (regulator of complement activation), SLAM (signaling lymphocyte activation molecule), nectin 4 (necently discovered epithelial cell receptor).
Measles fusion
F protein mediates fusion between viral envelope and host cell membrane
Measles replication and transcription
Catalyzed by viral RNA-dependent RNA polymerase (L and P), takes place in cytoplasm
Measles budding
Mediated by M protein, takes place at the plasma membrane.
Measles clinical course
Latent period of 10-14 days after spread via respiratory aerosols, 2-3 day prodromal fever, cough, conjunctivitis, rhinitis, followed by characteristic maculopapular rash. Onset of rash coincides with immune response and initation of viral clearance, recovery is accompanied by lifelong immunity.
Where does measles enter and where does it replicate/spread?
Virus transmitted through respiratory droplets and enters through the respiratory tract. Initial infection is established in the macrophages and dendritic cells of the respiratory tract. These infected cells transport the virus to local lymphoid tissue where it is amplified leading to viremia. Virus spreads through the blood to a number of organs infecting epithelial cells, endothelial cells, and tissue macrophages. See chart in slides.
Syncytium
Virus spread in tissue creates a giant multinucleated cell.
Koplik’s spots
Pinpoint gray-white spots (grains of salt-appearance) that appear on mucous membranes, most noticeable on the buccal mucosa.
Measles rash
begins on face, spreads to extremities, fever and severe symptoms diminish and the rash progresses
Complications from measles
Bacterial superinfection (5-15%): otitis media, mastoiditis, sinusitis, pneumonia. Immune suppression caused by infection can lead to complications, such as TB reactivation. Disease can be very severe in immunocompromised or malnourished patients. Postinfectious or acute disseminiated encephalomyelitis is an autoimmune demyelinating disease that occurs in 1/1000. 20% mortality.
How to diagnose measles
Clinical diagnosis: maculopapular rash for 3+days, fever, cough rhinitis conjunctivitis.
Laboratory diagnosis: RT PCR, virus antigen isolation from epithelial cells of nasopharynx.
When does appearance of the rash occur?
When immune response occurs and viral clearance begins.
How to treat measles?
No specific treatment available.
Measles Vaccine
Approved in 1963, edmonston strain attenuated by several passages in chick embryo fibroblasts, administered together with mumps and rubella. 12-15mos, then booster at 4-6 years.
Why do we wait until 12-15 months to vaccinate?
because maternal antibody decreases vaccine efficacy.
Why are high rates of vaccine coverage necessary to avoid outbreaks?
Because measles is so damn contagious!
Mumps
Caused by the mumps virus and presents with swelling of the salivary glands, particularly the parotid gland.
Characteristics of the mumps virus
Paramyxovirus family, genus rubulavirus. Negative strand, nonsegmented RNA virus, enveloped. Has HN, F, M, NPL,
Mumps Pathogenesis
Enters respiratory tract, virus grows in salivary glands and local lymphoid tissue. Virus spreads to spleen and distant lymphoid tissue (7-10 days). Then viremia occurs, causing diffuse disease.
Clinical aspects of mumps
Fever, meningitis, rare encephalitis, approx 30% are subclinical
Mumps vaccine
Live attenuated virus, single serotype, administered together with measles and rubella.
Rubella
German measles, mild disease w/ red maculopapular rash.
Rubella virus characteristics
Togavirus, positive strand RNA virus. Icosahedral nucleocapsid
Congenital rubella syndrome
If contracted in early months of pregnancy, rubella is associated with a high rate of birth defects like deafness, cataracts, heart defects.
Rubella vaccine
single serotype live attenuated virus vaccine
