Farm and Home Biosecurity
Consumer/General Public
Smallpox: Questions and Answers
Smallpox was once worldwide in scope, and before vaccination was practiced,
almost everyone eventually contracted the disease. The last naturally acquired
case of smallpox occurred in 1977. The last cases of smallpox, from laboratory
exposure, occurred in 1978. In the United States, routine vaccination against
smallpox ended in 1972. Since the vaccine is no longer recommended, the vaccine
is not available. An emergency supply of vaccine is maintained by the CDC and
can be released if necessary.
What are the Symptoms?
Smallpox is caused by variola virus. The incubation period is about 12 days
(range: 7 to 17 days) following exposure. Initial symptoms include high fever,
fatigue, and head and back aches. A characteristic rash, most prominent on the
face, arms, and legs, follows in 2 – 3 days. The rash starts with flat red
lesions that evolve at the same rate. Lesions become pus-filled and begin to
crust early in the second week. Scabs develop and then separate and fall off
after about 3 – 4 weeks. The majority of patients with smallpox recover, but
death occurs in up to 30% of cases.
How is it spread?
Smallpox is extremely infectious. The disease is spread from one person to
another by infected saliva droplets that expose a susceptible person having
face-to-face contact with the ill person. Persons with smallpox are most
infectious during the first week of illness, because that is when the largest
amount of virus is present in saliva. However, some risk of transmission lasts
until all scabs have fallen off. Although the scabs contain large amounts of
viable virus, epidemiological and laboratory studies indicate that they are not
particularly infectious. Contaminated clothing or bed linens can also spread the
virus. There are no known animal or insect reservoirs or vectors.
What about Vaccination?
Vaccination against smallpox is not recommended to prevent the disease in the
general public and therefore is not available.
In people exposed to smallpox, the vaccine can lessen the severity of or even
prevent illness if given within 4 days after exposure. Vaccine against smallpox
contains another live virus called vaccinia. The vaccine does not contain
smallpox virus.
Routine vaccination against smallpox ended in 1972. The level of immunity, if
any, among persons who were vaccinated before 1972 is uncertain; therefore,
these persons are assumed to be susceptible.
How is smallpox diagnosed?
Smallpox infection can be rapidly confirmed in the laboratory by electron
microscopic examination of vesicular or pustular fluid or scabs.
What is the Treatment?
No antiviral substances have yet proved effective for the treatment of
smallpox. Patients with the disease can benefit from supportive therapy
(intravenous fluids, medicine to control fever or pain, etc.) and antibiotics
for any secondary infections that occur.
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