INF2 - E. VARICELLA ZOSTER AND MEASLES VIRUS-COVERED Flashcards
1
Q
what does R0 denote
A
- number of people infected by one infectious person in a susceptible population
- if <1, no need for vaccine
2
Q
chickenpox and shingles
A
- caused by varicella zoster
- tropism for T-cells, epithelia and ganglia of CNS
- infectious 2 days before symptoms show
- primary infection = varicella (chickenpox)
clears in 1-2 weeks
calamine lotion on skin?
highly communicable: 90% become infected after exposure - latent infection = herpes zoster (shingles)
VZV stays in sensory nerve ganglia (innervate different parts of skin) and can reactivate
20% become infected after exposure
PEP - to high risk, Aciclovir?
3
Q
structure of VZV
A
- herpesviridae family and varicellovirus genus
- similar to HSV
- enveloped
- baltimore group 1
- dsDNA
- linear genome
- aka HHV-3
4
Q
how does VZV cause infection
A
- begins in epithelial cells of resp mucosa
- spread to tonsils and other lymphoid tissues
- spread by direct contact or inhalation of aerosolised fluid from acute varicella
- vesicular rash after 20-21 day incubation period (primary)
- infects sensory nerve cell (ganglia) in skin (latent)
- reactivated VZV - vesicular rash innervated by affected ganglia
5
Q
primary infection
A
- T-cells infected after replication in resp epithelial cells
- they enter lymphatic capillaries and systemic circulation
- T-cells transported around body, can transmit into skin
- lytic part of the cycle: rash, chickenpox
6
Q
lytic cycle
A
- VZV attaches to cell membranes of resp epithelium (and T-cell, ganglia) fuse and release uncoated capsid
- VZV DNA injected into nucleus
- expression of VZV proteins to make more capsid proteins and DNA replication
- nucleocapsids assemble, move to inner nuclear membrane
- bud acros to exit nucleus
- assembly and maturation in cytoplasm of host cell (ie - envelope and surface proteins)
- new virus particles transported and released from cell
7
Q
latent cycle
A
- infected ganglia cells
- viral replication stops at DNA duplication stage as:
no protein expression
no viral proteins found in nucleus
no new viruses made - no changes of cell morphology and no lysis
- reactivation - shingles
8
Q
symptoms of chickenpox
A
- rash on chest, back, face and entires body (4-7 days) - spots turn into itchy blisters
- harmless in healthy children
- skin infections and pneumonia (adults) - complications
- fever
- headache
- tiredness
- decreased appetite
9
Q
symptoms of shingles
A
- risk factors: increasing age and immunocompromised
- postherpetic neuralgia (intermittent nerve pain) is a common complication
10
Q
measles
A
- caused by measles virus (MeV)
- viral resp illness:
1. cough, coryza, conjunctivitis
2. koplik spots in buccal mucosa
3. maculopapular rash on body - infectious 4 days before symptoms show
- tropism for macrophages, lymphocytes, dendritic cells, epithelia (mucosal membrane in skin + mouth)
- very contagious
- 9/100 infected after exposure
- notifiable diaseas
- MMR vaccine
11
Q
measles virus structure
A
- paramyxoviridae family
- morbillivirus genus
- enveloped
- baltimore group 5
- ssRNA
- linear genome
- genome has 6 genes encoding important proteins to make new copies of itself
- viral polymerase (L) and surface proteins (H and F)
12
Q
genotypes
A
- many MeV genotypes (if sequenced ran, would be differences) but only one serotype (ie same surface proteins so antibodies for one genotype work against another)
- H1 most frequent (endemic in China)
- B3 and D8 most widely distributed
13
Q
infection with measles
A
- transmitted by direct contact with droplets or inhalation of aerosolised fluid
- initially targets tissue-resident DCs and macrophages in resp tract (express SLAM receptor)
- MeV multiples in regional lymphoid tissues - sys infection
- infected cells migrate and transmit MeV to epithelial cells
- use nectin 4 as receptor
- infection in epithelia and more viruses released into resp tract
- breathe, pass on infectious particles
14
Q
measles life cycle
A
- transmembrane glycoproteins (H and F) in lipid envelope mediate receptor binding and membrane fusion
- signalling lymphocyte activation molecules (SLAM) is host cellular receptor H protein of MeV binds
- ssRNA released: genome replication in cytoplasm then assembly and release
(as proteins expressed and made, new copies of genetic material made so they but off and infect new cells)
15
Q
symptoms of measles
A
- after it spreads to peripheral lymphoid tissues - prodromal phase starts
- malaise
- fever
- cough
- white lesions: koplik spots appear on buccal mucosa
- infected lymphocytes have disseminated MeV to peripheral tissues
- maculopapular skin rash (flat and raised parts) and conjunctivitis (can cause photophobia)
- rash starts behind ears or on face, spreads to trunk
- caused by immune mediated clearance of MeV-infected cells
