**SMALLPOX FACT SHEET**

**Smallpox Overview**

# The Disease

Smallpox is a serious, contagious, and sometimes fatal infectious
disease. There is no specific treatment for smallpox disease, and the
only prevention is vaccination. The name *smallpox* is derived from the
Latin word for "spotted" and refers to the raised bumps that appear on
the face and body of an infected person.

There are two clinical forms of smallpox. Variola major is the severe
and most common form of smallpox, with a more extensive rash and higher
fever. There are four types of variola major smallpox: ordinary (the
most frequent type, accounting for 90% or more of cases); modified (mild
and occurring in previously vaccinated persons); flat; and hemorrhagic
(both rare and very severe). Historically, variola major has an overall
fatality rate of about 30%; however, flat and hemorrhagic smallpox
usually are fatal. Variola minor is a less common presentation of
smallpox, and a much less severe disease, with death rates historically
of 1% or less.

Smallpox outbreaks have occurred from time to time for thousands of
years, but the disease is now eradicated after a successful worldwide
vaccination program. The last case of smallpox in the United States was
in 1949. The last naturally occurring case in the world was in Somalia
in 1977. After the disease was eliminated from the world, routine
vaccination against smallpox among the general public was stopped
because it was no longer necessary for prevention.

# Where Smallpox Comes From

Smallpox is caused by the variola virus that emerged in human
populations thousands of years ago. Except for laboratory stockpiles,
the variola virus has been eliminated. However, in the aftermath of the
events of September and October, 2001, there is heightened concern that
the variola virus might be used as an agent of bioterrorism. For this
reason, the U.S. government is taking precautions for dealing with a
smallpox outbreak.

# Transmission

Generally, direct and fairly prolonged face-to-face contact is required
to spread smallpox from one person to another. Smallpox also can be
spread through direct contact with infected bodily fluids or
contaminated objects such as bedding or clothing. Rarely, smallpox has
been spread by virus carried in the air in enclosed settings such as
buildings, buses, and trains. Humans are the only natural hosts of
variola. Smallpox is not known to be transmitted by insects or animals.

A person with smallpox is sometimes contagious with onset of fever
(prodrome phase), but the person becomes most contagious with the onset
of rash. At this stage the infected person is usually very sick and not
able to move around in the community. The infected person is contagious
until the last smallpox scab falls off.

+---------------+------------------------------------------------------+
| # Sma         |                                                      |
| llpox Disease |                                                      |
+---------------+------------------------------------------------------+
| **Incubation  | **Exposure to the virus** is followed by an          |
| Period**      | incubation period during which people do not have    |
|               | any symptoms and may feel fine. This incubation      |
| **(Duration:  | period averages about 12 to 14 days but can range    |
| 7 to 17       | from 7 to 17 days. During this time, people are not  |
| days)**       | contagious.                                          |
|               |                                                      |
| ***Not        |                                                      |
| contagious*** |                                                      |
+---------------+------------------------------------------------------+
| **Initial     | The **first symptoms** of smallpox include fever,    |
| Symptoms      | malaise, head and body aches, and sometimes          |
| *             | vomiting. The fever is usually high, in the range of |
| (Prodrome)*** | 101 to 104 degrees Fahrenheit. At this time, people  |
|               | are usually too sick to carry on their normal        |
| **(Duration:  | activities. This is called the *prodrome* phase and  |
| 2 to 4        | may last for 2 to 4 days.                            |
| days)**       |                                                      |
|               |                                                      |
| ***Sometimes  |                                                      |
| co            |                                                      |
| ntagious\**** |                                                      |
+---------------+------------------------------------------------------+
| **Early       | A **rash emerges** first as small red spots on the   |
| Rash**        | tongue and in the mouth.                             |
|               |                                                      |
| **(Duration:  | These spots develop into sores that break open and   |
| about 4       | spread large amounts of the virus into the mouth and |
| days)\        | throat. At this time, the person becomes **most      |
| *Most         | contagious**.                                        |
| contagious*** |                                                      |
|               | Around the time the sores in the mouth break down, a |
| **Rash        | rash appears on the skin, starting on the face and   |
| di            | spreading to the arms and legs and then to the hands |
| stribution:** | and feet. Usually the rash spreads to all parts of   |
|               | the body within 24 hours. As the rash appears, the   |
| ![](media/i   | fever usually falls and the person may start to feel |
| mage1.png){wi | better.                                              |
| dth="1.510416 |                                                      |
| 6666666667in" | By the third day of the rash, the rash becomes       |
| height        | raised bumps.                                        |
| ="1.78125in"} |                                                      |
|               | By the fourth day, the bumps fill with a thick,      |
|               | opaque fluid and often have a depression in the      |
|               | center that looks like a bellybutton. (This is a     |
|               | major distinguishing characteristic of smallpox.)    |
|               |                                                      |
|               | Fever often will rise again at this time and remain  |
|               | high until scabs form over the bumps.                |
+---------------+------------------------------------------------------+
| **Pustular    | The bumps become **pustules**---sharply raised,      |
| Rash**        | usually round and firm to the touch as if there's a  |
|               | small round object under the skin. People often say  |
| **(Duration:  | the bumps feel like BB pellets embedded in the skin. |
| about 5       |                                                      |
| days)**       |                                                      |
|               |                                                      |
| ***           |                                                      |
| Contagious*** |                                                      |
+---------------+------------------------------------------------------+
| **Pustules    | The pustules begin to form a crust and then          |
| and Scabs**   | **scab**.                                            |
|               |                                                      |
| **(Duration:  | By the end of the second week after the rash         |
| about 5       | appears, most of the sores have scabbed over.        |
| days)**       |                                                      |
|               |                                                      |
| ***           |                                                      |
| Contagious*** |                                                      |
+---------------+------------------------------------------------------+
| **Resolving   | The scabs begin to fall off, leaving marks on the    |
| Scabs**       | skin that eventually become pitted **scars**. Most   |
|               | scabs will have fallen off three weeks after the     |
| **(Duration:  | rash appears.                                        |
| about 6       |                                                      |
| days)**       | The person is contagious to others until all of the  |
|               | scabs have fallen off.                               |
| ***           |                                                      |
| Contagious*** |                                                      |
+---------------+------------------------------------------------------+
| **Scabs       | Scabs have fallen off. Person is no longer           |
| resolved**    | contagious.                                          |
|               |                                                      |
| ***Not        |                                                      |
| contagious*** |                                                      |
+---------------+------------------------------------------------------+

\*Smallpox may be contagious during the *prodrome* phase, but is most
infectious during the first 7 to 10 days following rash onset.

For more information, visit
[www.cdc.gov/smallpox](http://www.cdc.gov/smallpox), or call CDC at\
800-CDC-INFO (English and Spanish) or 888-232-6348 (TTY).

August 9, 2004