Download Chapter 34 Poxviruses

Poxviruses
Chapter 34
Properties of Poxviruses
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Structure and composition
Largest viruses
dsDNA, 130-375 kb
Brick shaped
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Core
“dumbbell” core (contains nucleic acid)
Lateral bodies (unknown function)
Enveloped
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Resistant to inactivation
More than 100 polypeptides
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Many target the immune response
Replicate in cytoplasm
Tend to be highly species-specific
Some are being explored as gene therapy vectors
Envelope
Lateral
bodies
Classification
Family Poxviridae
Subfamilies
Genera
Members
Chordopoxvirinae
Orthopoxvirus
Variola, vaccinia, cowpox, monkeypox, camelpox
(vertebrates)
Parapoxvirus
Sealpox, parapox of deer, pseudocowpox
Avipoxvirus
Canarypox, fowlpox, pigeonpox, turkeypox, penguinpox
Capripoxvirus
Goatpox, sheeppox
Leporipoxvirus
Hare fibroma, myoma, rabbit fibroma, squirrel fibroma
Suipoxvirus
Swinepox
Molluscipoxvirus
Molluscum contagium
Yatapoxvirus
Tanapox, Yaba monkey tumor
Entomopoxvirinae
Capripoxvirus A
(insects)
Capripoxvirus B
Capripoxvirus C
Replication
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Attachment, penetration and uncoating
Membrane fusion
Viral core dissociates, releasing
Viral DNA
Viral enzymes
Virally-encoded RNA polymerase (prepackaged) synthesizes
early mRNA
Early proteins
DNA polymerase
Thymidine kinase
Recombinase?
Maturation
Structural proteins are synthesized
Virus synthesizes its own membranes
Some virus exits by budding, but most when the cell dies
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Smallpox
• Named smallpox to discriminate it from
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largepox (syphilis)
No animal reservoir
Two species
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Variola major (20% fatality; Genbank #VVCGAA)
Variola minor (1-2% fatality; Genbank #VMVY16780)
Smallpox has shaped civilization
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Earliest evidence: Egyptian mummies
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Introduced to the Americas by European explorers
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Ramses V (1157 BC)
British army used smallpox as a biological weapon
against the Pontiac Indians
About 40 million native Americans died from
European diseases, including smallpox
Native Americans have limited MHC
polymorphisms
Killed 300 million people in the 20th century alone
Total fatalities probably near 1 billion
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Control and Eradication
Vaccine
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Edward Jenner observed that milkmaids rarely contracted
smallpox
All had recalled earlier cowpox infections, which were nearly
universal in milkmaids
Cowpox only causes a mild infection in humans
Jenner hypothesized that the infectious agent of cowpox protected
against smallpox
He inoculated a nephew by scarification with cowpox crusts
termed variolation
Today’s vaccine is live attenuated vaccinia virus
Vaccinia’s genome looks similar to cowpox, but it is not
identical
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Smallpox
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In the 1950s, the Soviets proposed a global eradication
program to the United Nations
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Some have suggested that the Soviets had a vaccine-resistant
strain of variola, which could be used as a bioweapon
The World Health Organization (WHO) Intensified Smallpox
Eradication Programme program began in 1967
Smallpox was declared eradicated in 1980 (last case in 1977)
Only two nations are supposed to have smallpox viruses today
United States (CDC-Atlanta)
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Smallpox Pathogenesis
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Respiratory transmission
Incubation period 10-14 days
After day 7 or so, humans begin shedding virus
asymptomatically
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Principal reason for rapid spread
Outbreaks tended to be in clusters
Allowed the ring immunization containment strategy during the
eradication program
Clinical symptoms
Fever
Malaise
Centrifugally-distributed exanthems
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macules
papules
pustules
Clinical
progression of
smallpox
Smallpox Pathogenesis in an Animal
Model
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Problem: Smallpox virus was only known to infect humans
Can an animal model be developed to study pathogenesis?
No cases of smallpox since the 1970s
Modern science could learn much from studying the course of
infection and immune response in an animal model
Because of 9/11, CDC and USAMRIID Scientists were granted
permission by the WHO to infect cynomolgus macaques with
smallpox in an attempt to assess pathogenesis using contemporary
laboratory techniques
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Jahrling et al. PNAS. 101:15196-15200
Rubins et al. PNAS. 101:15190-15195
Required highest containment: BSL-4
Required >109 pfu iv for infection
Resulted in fulminant disease fatal in most monkeys
Jahrling et al.
with smallpox virus infection of
monkeys. (a) Hemorrhage on
the serosal surface of the distal
colon, monkey I-7, 6 days after
exposure. Note the diffuse
petechial hemorrhages and
hemorrhagic, colic lymph nodes.
(b) Mucosal surface of the distal
colon described in a. Note the
severe congestion, hemorrhage,
and hemorrhagic colic lymph
nodes. (c) Medial surface of the
right arm of monkey I-4, 9 days
after exposure. Smallpox
pustules are predominantly
discrete with occasional
coalescence. Pock lesions
developed synchronously and
were more numerous distally,
which is consistent with
centrifugal distribution. (d)
Palmar surface of the left hand
of a monkey 11 days after
exposure. Discrete and
coalescing pustules retained
integrity due to heavily
keratinized palmar and digital
epidermis. (e) Upper lip and
nostrils from a cynomolgus
monkey 11 days after exposure.
Note synchronous development
of pustules, some of which have
umbilicated. Pustules that
formed on the lightly keratinized
mucosal surfaces of the nostrils
Fig. 4. Immunofluorescence examination of tissues from nonhuman primates infected with variola. (a) Staining for
monocytes/macrophages (green) and viral antigen (red) indicated the presence of infected monocytes/macrophages (gold) in
the lymphoid tissues (lymph node shown) and in circulation. (b) In addition to monocytes/macrophages, virus-infected
endothelial cells (green) were readily observed. (c) Staining for monocytes/macrophages (green) and apoptosis (red) revealed
the presence of numerous tingible body macrophages in lymphoid tissues. The majority of apoptotic cells were not
monocytes/macrophages but instead were lymphocytes. A rare apoptotic monocyte/macrophage (arrow) is shown. (d) A
monocyte/macrophage with a clearly stained nonapoptotic nucleus (blue) is shown engulfing two separate apototicJahrling
bodies. et al.
Fig. 5. Concentrations of D dimers,
cytokines, and chemokines
sequentially obtained from variolainfected monkeys. (a) D dimers
(µg/ml) in sera of monkeys that
received graded doses of variola
strain India 1724 i.v. (b) IL-8
concentrations (pg/ml). (c)
Monocyte chemoattractant protein 1
concentrations (pg/ml). (d)
Macrophage inflammatory protein 1
concentrations (pg/ml). (e) IL-6
concentrations (pg/ml) in the sera of
three monkeys infected i.v. with
Harper strain (109 pfu). (f) Mean (±
1 SD) IFN- concentrations (pg/ml) in
sera of monkeys infected i.v. with
India 7124 and Harper strains (109
pfu).
Jahrling et al.
Host Genes Expressed During
Smallpox
Smallpox as a Biological
Weapon
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Variola viruses do not exist in nature
Some nations are suspected of having active
bioweapons programs
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North Korea
Syria
Iran
Israel
Russia
Some may have kept smallpox stocks hidden
The world is ill-prepared for smallpox
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Vaccination is no longer routine
Thus, a large susceptible population
Monkeypox
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2003 US Outbreak
72 Cases
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Wisconsin, Illinois, Indiana
Kansas, Missouri, Ohio
Introduced from Africa to US pet supplier
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Gambian giant rat
Prairie dogs
Infection was not fatal to humans
In Africa, disease is fatal in 1-10% of cases
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Democratic Republic of Congo - 10%
West Africa - 1-2%
The US strain was from west Africa
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Genomic comparisons revealed 5 genes mutant or
missing in West African strains compared to central
African strains
WA strains do not have D14L, a protein that disables
complement enzyme activity, while central African do