1. Biological Terrorism
Smallpox
5/9/01

2. History Caused by variola virus Most deaths of any infectious disease
~500 million deaths in 20th Century
~2 million deaths in 1967
Known in ancient times
Described by Ramses
Natural disease eradicated
Last U.S. case – 1949 (imported)
Last international case – 1978
Declared eradicated in 1979
Photo: National Archives

3. Bioweapon Potential Features making smallpox a likely agent
Can be produced in large quantities
Stable for storage and transportation
Known to produce stable aerosol
High mortality
Highly infectious
Person-to-person spread
Most of the world has little or no immunity

4. Bioweapon Potential Prior attempted use as bioweapon
French and Indian Wars ( )
British gave Native Americans infected blankets
Outbreaks ensued, some tribes lost 50%
Allegations of use in U.S. Civil War
Alleged use by Japanese in China in WWII

5. Bioweapon Potential Current concerns
Former Soviet Union scientists have confirmed that smallpox was successfully weaponized for use in bombs and missiles
Active research was undertaken to engineer more virulent strains
Possibility of former Soviet Union virus stock in unauthorized hands

6. Bioweapon Potential Nonimmune population Availability of virus
<20% of U.S. with substantial immunity
Availability of virus
Officially only 2 stocks (CDC and Russia)
Potential for more potent attack
Combined with other agent (e.g. VHF)
Engineered resistance to vaccine

7. Bioweapon Potential Delivery mechanisms Aerosol
Easiest to disperse
Highest number of people exposed
Most contagious route of infection
Most likely to be used in bioterrorist attack
Fomites- any object or substance capable of carrying infectious organisms
Theoretically possible but inefficient

8. Epidemiology All ages and genders affected Incubation period
From infection to onset of prodrome
Range 7-17 days
Typical days

9. Epidemiology Transmission Airborne route known effective mode
Initially via aerosol in BT attack
Then person-to-person
Hospital outbreaks from coughing patients
Highly infectious
<10 virions sufficient to cause infection
Aerosol exposure <15 minutes sufficient

10. Epidemiology
Infectious Materials
Saliva
Scabs
Urine
Possibly blood

11. Epidemiology Mortality 25-30% overall in unvaccinated population
Infants, elderly greatest risk (>40%)
Higher in immunocompromised
May be dependent on ICU facilities
Dependent on virus strain
Dependent on disease variant

12. Epidemiology Factors that allowed smallpox eradication Slow spread
Effective, relatively safe vaccine
No animal/insect vectors
No sig. carrier state (infected die or recover)
Infectious only with symptoms
Prior infection gives lifelong immunity
International cooperation

13. Clinical Features Three stages of disease
Incubation- From time of infection to onset of symptoms
Average days (range 7-17)
Asymptomatic
Prodromal
Nonspecific febrile illness, flu-like
Eruptive
Characteristic rash

14. PICS

15. Classic Centrifugal Rash of Smallpox Involving Face and Extremities,
Including the Soles.
Photo: National Archives

16. Classic Centrifugal Rash of Smallpox Involving Face and Extremities.
Photo: National Archives

17. Classic Smallpox Rash, Demonstrating Same Development Stage (Pustular) of All Lesions in a Region
Photo: National Archives

18. Discrete Type of Classical Smallpox Rash
Photo: National Archives

19. Confluent Type of Classical Smallpox Rash
Photo: National Archives

20. Diagnosis Traditional confirmatory methods Newer rapid tests
Electron microscopy of vesicle fluid
Rapidly confirms if orthopoxvirus
Culture on chick membrane or cell culture
Slow, specific for variola
Newer rapid tests
Available only at reference labs (e.g. CDC)
PCR, RFLP

21. Prevention Vaccination policies Stability
Last mandated in U.S. in 1972
World travelers until 1979
Laboratory workers
Stability
Freeze-dried lasts decades
Current stock probably still potent

22. Prevention Supply Production 7-15 million doses in U.S. as of 1999
>20 years old
Stock controlled by CDC
Production
No current active production
the U.S. government has enough vaccine to vaccinate every person in the United States in the event of a smallpox emergency