L22 - Smallpox Flashcards
how is smallpox spread
secretions from nose and mouth
= respiratory disease
how long after exposure do people develop symptoms
2 weeks
is smallpox related to chickenpox
No
= early rash is often confused with chickenpox
pathogen of smallpox
dsDNA virus = Variola
what is special about smallpox/variola
first disease to be controlled by vaccination
= completely removed from environment
progression of symtpoms for smallpox
Fever - 2 weeks after exposure
2-4 days after fever rash begins to develop
= rash devlops into smallpox
symtpoms - smallpox vs chicken pox
smallpox victims have pox on soles of feet and palms of hand
= very rare in chicken pox
pox is more in extremities and arms/legs than chicken
fever is BEFORE the rash in smallpox
name of family of viruses smallpox comes from
Poxviridae
= includes Vaccinia = the vaccine virus
also includes poxes for a range of animals:
- monkeypox
- camel pox
- cowpox
describe variolas structure
dsDNA virus
brick shaped with multiple lipid envelopes and a core
core holds linear DNA
lateral bodies outside of core
- hold viral proteins for infection
= virus structure is complex and poorly understood
replication cycle of smallpox
- Virus binds and invades into cytoplasm host
- uncoats outermembrane and inner core membrane surrounding genome
- production of early genes via pre-synthesied RNA polymerase
= DNA polymerase/replicative elements
- virus replicates at ‘Viral factories’ in cytoplasm
- once replicated late genes are expressed and new viral molecules formed
what is unique as a DNA virus about smallpox
rreplicates entirely in cytoplasm
= viral factories
describe the variolas genome
linear dsDNA genome
ends of nucletides contain inverted terminal repeat sequences
= tandem repeats and palindromic sequnces
Hairpin loops at very end of DNA formed by palindromic sequnces folding back on themselves
= covalent bonds
= protect from nucleases
what does variola carry with it for ‘early’ gene expression and what is amde in early gene expression for ‘late’ proteins
pre-synthesised RNA polmerase
= genome also holds genes for DNA polymerases
= substitute for host cells
what is variolation - before vaccination
deliberatley infecting sombody with parts of infected people
brief history of smallpox vaccination
Chinese and Indian cultures used variolation for a long time
Lady montague introduced variolation to UK in 1720s
Edward jenner began infecting ppl with cowpox
= found that they didnt get smallpox
roles of cell-mediated and humoral immunity in fighting smallpox
cell mediated:
clearing the infection and survival
humoral:
long term protection from reinfection
why was smallpox a good candidate for worldwide eradication
Humans are the only host - no animal resevoir
= once eradicated from us its gone completely
virus is a single stable serotype
= no antigenic shift or adaptations = no new vaccine needed
symtpoms were easily observable = receive treatment quickly
history of worldwide eradication of smallpox
1960s the WHO begain worldwide programme of vaccination
accidental infectioon in birmingham killing 2 ppl
1980 = declared smallpox free
how many labs in the world hold a strain of variola/smallpox
2
= there are only 2 places in the UK with high enough safety measures to contain it
= none in UK currently
pros and cons of destroying the last stocks of variolka virus
+ risk of bioterrorism and a largely unvaccinated population
- Pathogenisis of virus still not undertsood - could learn more
knowledge could be helpful IF bioterrorism was used
describe how the Modified Vaccinia Ankara (MVA) vaccine was developed
VAccinia strain was passaged into chicken cells over and over
over time virus lost 10% of genome
= affected virus ability to infect mammilian cells
the vaccine still produces strong immune response for protection BUT limited replication
