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Smallpox is a viral disease characterized by a skin rash and a high death rate.
Smallpox is a disfiguring and potentially deadly infectious disease caused by the Variola major virus. Before smallpox was eradicated, there were two forms of the disease worldwide: Variola major, the deadly disease, and Variola minor, a much milder form. According to some health experts, over the centuries smallpox was responsible for more deaths than all other infectious diseases combined. Currently, there is no evidence of naturally occurring smallpox transmission anywhere in the world.

Causes, and risk factors

Smallpox was once found throughout the world, causing illness and death wherever it occurred. Smallpox was primarily a disease of children and young adults, with family members often infecting each other.
Risk factors for smallpox include being a laboratory worker who handles the virus (rare), or being in the environment where the virus was released as a biological weapon.
It is conceivable that smallpox could be deliberately reintroduced into the population. Smallpox could be released by aerosol, and it would spread easily because the virus remains very stable in aerosol form.
Smallpox is highly contagious from one person to another. It is most contagious during the first week, and is spread from saliva droplets. It may continue to be contagious until the scabs from the rash fall off. It may also be spread from bed sheets and clothing.
Researchers believe that the smallpox infection (if released in aerosol form, under favorable conditions, without sunlight) could remain viable for as long as 24 hours. In unfavorable conditions, the virus may only remain viable for 6 hours. There is clear evidence that shows that the virus can remain viable on bed linens and clothes for significant periods of time.


Smallpox is highly contagious. In most cases, people get smallpox by inhaling droplets of saliva, which are full of virus, during face-to-face contact with an infected person. When someone becomes infected, they do not immediately feel sick or shed virus to their household contacts. In addition, they have no symptoms for 10 to 12 days. After the virus has multiplied and spread throughout the body, a rash and fever develop. This is the "illness" portion of the disease, and it's when someone is most infectious.
Some risk of transmission lasts, however, until all scabs have fallen off. Contaminated clothing or bed linens also can spread the virus. Those caring for people with smallpox need to use special safety measures to ensure that all bedding and clothing from the infected person are cleaned appropriately with bleach and hot water. Caretakers can use disinfectants such as bleach and ammonia to clean contaminated surfaces.


Smallpox has two forms: 1) Variola major -- which is a serious illness with a mortality rate according to the CDC of 30% or more, in unvaccinated people, and 2) Variola minor -- a milder infection. The incubation period for smallpox is approximately 12-14 days. The symptoms are:
  • High fever
  • Fatigue
  • Severe headache
  • Backache
  • Malaise
  • Rash, raised and pink on the skin, starting centrally and spreading outwards. (First the mucosa of the mouth and throat, then face, forearms, trunk, and legs. Rash turns to pus-filled lesions that become crusty on the eighth or ninth day.)
  • Delirium
  • Vomiting and diarrhea
  • Excessive bleeding

A characteristic rash, most prominent on the face, arms, and legs, follows 2 to 3 days after the first symptoms. The rash starts with flat red lesions (sores) that develop at the same rate. After a few days, the lesions become filled with pus. They begin to crust early in the second week. Scabs develop and then separate and fall off after about 3 weeks.

Signs and tests
  • Virus can be seen by electron microscope and by culture.
  • Low white blood cell count initially, that increases later in the disease.
  • Low platelet count.
  • DIC panel can be positive in cases of hemorrhage.
  • Antibodies turn positive soon after the infection is complete

There is no proven treatment for smallpox. People with the disease can benefit from intravenous fluids and medicine to control fever or pain as well as antibiotics for any secondary bacterial infections that may occur. If an infected person gets the smallpox vaccine within 4 days after exposure to the virus, it may lessen the severity of illness or even prevent it. The majority of people with smallpox recover, but death may occur in up to 30 percent of cases. Those who do recover are often left with disfiguring scars.
If the smallpox vaccination is given within 1-4 days of exposure to the disease, it may prevent illness, or at least lessen the degree of illness associated with the disease. Treatment, once the disease symptoms have started, is limited.
There is no agent that has been specifically made for treating smallpox. Sometimes antibiotics are given for secondary infections that may occur. Vaccinia immune globulin (antibodies against a disease similar to smallpox) may help shorten the disease.
If a diagnosis of smallpox were made, exposed persons would need to be isolated immediately. The isolation would include not just the person who contracted the disease, but all other face-to-face contacts with that person.

  • Bacterial infections at the skin at the sites of the lesions
  • Pitted scars from pustules
  • Arthritis and bone infections
  • Pneumonia
  • Severe bleeding
  • Eye infections
  • Brain inflammation (encephalitis)
  • Death

To prevent the spread of smallpox, health care providers must
  • Isolate infected people
  • Vaccinate close contacts of infected people

The currently licensed smallpox vaccine, which consists of a laboratory strain of vaccinia virus, is highly effective in preventing infection. Medical experts believe the vaccine may lessen the severity of, or even prevent, illness in unvaccinated people if given within 4 days of exposure to the virus.
The smallpox vaccine helps the body develop immunity to smallpox. The vaccine is made from a "pox"-type virus related to smallpox. The smallpox vaccine contains live vaccinia virus-unlike many other vaccines that use killed virus. The vaccine does not contain the smallpox virus and cannot transmit smallpox.

Getting the vaccine

Health care providers do not use a hypodermic needle, usually used for vaccinations, to give the smallpox vaccine. Instead, they use a tiny, two-pronged needle that is dipped into the vaccine solution. When removed from the solution, the needle keeps a droplet of the vaccine. The needle is used to prick the skin, usually in the upper arm, a number of times within a few seconds. The pricking is not deep, but it will cause a sore spot and one or two droplets of blood.
If the vaccination is successful, a red and itchy bump develops at the vaccine site in 3 or 4 days.
  • In the first week, the bump becomes a large blister, fills with pus, and begins to drain.
  • During the second week, the blister begins to dry up and a scab forms.
  • In the third week, the scab falls off, leaving a small scar.
People who get the vaccine for the first time have a stronger reaction than those who are revaccinated.

Reactions and complications

Most people experience normal, typically mild reactions to the vaccine, which go away without treatment. The vaccine often causes a low fever, swollen glands in the armpits, as well as skin redness at the vaccination site.
The vaccine, however, can cause several complications, some life-threatening, particularly in people with immune deficiencies and skin disorders. Based on reactions to smallpox vaccines in the past, people vaccinated for the first time will have potentially life-threatening complications that require medical attention, including
  • Eczema vaccinatum (EV)-spread of vaccinia skin lesions to areas of the body once or presently afflicted by eczema.
  • Progressive vaccinia-uncontrolled spread of the vaccinia virus to adjacent and underlying tissues resulting in tissue death.
  • Postvaccinal encephalitis-spread of the vaccinia virus to the central nervous system that is probably made worse by an over-response to the vaccine by the immune system.
  • Myo/pericarditis-an inflammation of the heart that is probably also caused by an over-response to the vaccine by the immune system.


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