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Smallpox, a potential problem
Julia Higgins
MSc Molecular Medical
Microbiology
Contents
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Introduction and History
Epidemiology and Transmission
Microbiology and Pathogenesis
Clinical Features
Methods to counteract pre-exposure and postexposure
• Potential as a Bioterrorist Weapon
• Conclusion
Introduction and History
Introduction
• Smallpox (Variola) feared
most devastating of all
infectious diseases
• WHO declared smallpox
extinct 1980
• Consequently no further
need for immunisation
programs
History
• Smallpox illness of
humans 3,000 years
• Edward Jenner, father of
smallpox vaccination 1798
• Smallpox largely
eradicated early 20th
Century
Epidemiology & Transmission
• Only officially exists in two laboratories in World:
CDC Atlanta USA & Koltsovo former USSR
• Transmission mainly via airborne route
• Only person to person, no animal reservoir or insect
vector
• Can be via direct contact of vesicle fluid, saliva and
respiratory secretions
• Contaminated linen and clothing
Microbiology & Pathogenesis
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Microbiology
Member of genus
Orthopoxvirus
Double-stranded DNA
virus
Virion brick-shaped
structure ~200nm
diameter
Uses host enzymes for
replication
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Pathogenesis
Infective dose believed to
be only few virions
Migration &
multiplication in lymph
nodes
Asymptomatic viremia
20 viremia followed by
fever
Clinical Features
• Incubation period ~ 12 days
• Flu-like symptoms
• Lesions to macules to papules to vesicles to
pustules
• Scabbing of pustules
Table 1: Comparison in onset, symptoms and rates of fatality in variations of Smallpox
Infections
Type
Infection
Incubation
Period
Diagnostic
Symptoms
Rate of
Fatality
Variola Minor
(alastrim)
12 days
Sparse rash
< 1%
Variola Major
(90% cases)
12 days
Maculopapular rash
30%
Malignant
Variant
Abrupt onset
Confluent lesions
Frequently fatal
Hemorrhagic
Variant
Considerably
less than
minor and
major variants
Dusky erythema
followed by
petechiae
Uniformly fatal
Smallpox lesions on skin of trunk. Picture taken in
Bangladesh, 1973. Public Health Images Library (PHIL) ID
# 284. Source: CDC/James Hicks
A Practical treatise on
smallpox : illustrated
by coloured
photographs from life
/ by George Henry Fox
; with the
collaboration of S.D.
Hubbard, S. Pollitzer,
and J.H. Huddleston.
Philadelphia :
Lippincott, c1902
Figure 1. Typical Temperature Chart of Patient With
Smallpox Infection
Temperature 0C
40.5
40
Rash
_ _ _ _ _ Scabbing
39.5
39
38.5
38
37.5
37
10
12
14
16
18
20
22
24
26
28
30
32
Days of Infectivity
Chart adapted from JAMA June 9th 1999
Measures to counteract preexposure and post-exposure
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Pre-exposure
Natural immunity from
previous exposure to virus
Routine vaccination –
Completely stopped in
1979 as recommended by
WHO.
Vaccination only effective
for 10 years
Previous vaccination
reduces effects of virus
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Post-exposure
Vaccine up to 4 days after
exposure to virus
No Antiviral therapy
except treatment of
symptoms
Compounds cidofovir and
adefovir
Cidofovir evidence of
promising results
Potential as a Bioterrorist Weapon
• Widespread immunity no longer in population
• Increase in immune disorders results in increased
fatality
• Only 90 million vaccines readily available
worldwide (15.4 million USA alone)
• Rate of transmission estimated at 10-20 new
infections per infected person
• Reports from Ken Alibek of successful programs
to produce smallpox in large quantities
Conclusion
• Worldwide need to produce sufficient supply of
vaccines to combat potential deliberate release
• Worldwide need to mass produce bifurcated needle to
administer vaccines
• Merck & Company to mass produce vaccines for USA
• Research to develop antiviral drugs to treat virus
• Because of the lack of immunity all the above need to
be addressed post haste in the event of an intentional
release
• As it stands the release of smallpox would pose a
potential danger