Smallpox Life Cycle

The Variola virus is an infectious pathogen that causes the disease smallpox. Smallpox is a contagious and serious disease that is often fatal. According to the Centers for Disease Control, toward the end of the 20th century, smallpox was virtually eradicated as a disease, due to a worldwide vaccination program.

Initial Infection and Incubation Phase

• Smallpox spreads by direct, long-term, face-to-face contact with an infected person or by contact with infected body fluids or contaminated objects such as clothing. Smallpox is rarely spread through airborne transmission and is not known to be transmitted by animals or insects. The incubation period lasts from seven to 17 days, during which infected individuals often show no symptoms and are not contagious.

Prodrome Phase

• Smallpox begins with a high fever between 101° and 104° Fahrenheit, headache, body pain, tiredness, and sometimes vomiting, usually lasting two to four days. At this time, infected persons are generally too ill to carry on normal activity. During this phase, they may be contagious.

Early Rash Phase

• This phase usually lasts for four days and is the most contagious phase of the illness. This rash first appears as small red spots in the mouth and on the tongue that will eventually produce open sores that spread the virus. Next, a rash will appear on the skin beginning on the face and spreading to the torso and extremities within 24 hours. During this time, the individual may experience a fall in the temperature of the fever and may feel better.

  On the third day, raised bumps will appear within the rash. About 24 hours later, the bumps will begin to fill with thick, opaque liquid. The bumps may exhibit bellybutton-like depressions that are typical of this phase of the disease. Fever may return and may remain until scabs formed over the bumps.

Pustular Rash Phase and Scabs Phase

• The bumps will eventually become raised pustules that are round and firm to the touch. The pustules usually last for about five days in this state. After five more days, the pustules will start to ooze. Scabs will eventually form. During these phases, the infected person is still contagious.

Resolving Scabs

• After a while, the scabs will fall off, leaving marks that will form scars on the skin. The scabs usually completely resolve after about six days, at which time, the person will no longer be contagious.

Treatment

• As of now, no known treatment for an active infection of smallpox exists, other than managing the symptoms. Because smallpox is extremely virulent, outbreak management should be started immediately upon identification of infection.

  Vaccines are available to provide immunity against smallpox. These can be administered up to four days after exposure to provide protective immunity.

Forms of the Disease

• Variola major and variola minor are the two main forms of the disease, both with similar signs and symptoms. Variola major is fatal in 30 percent of those infected, while Variola minor is fatal in less than one percent of the infected population. There are two rare forms of smallpox called hemorrhagic and malignant which are usually fatal.