Variola virus (Smallpox Virus)


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Thousands of years ago, variola virus (smallpox virus) emerged and began causing illness and deaths in human populations, with smallpox outbreaks occurring from time to time. Thanks to the success of vaccination, the last natural outbreak of smallpox in the United States occurred in 1949. In 1980, the World Health Assembly declared smallpox eradicated (eliminated), and no cases of naturally occurring smallpox have happened since.

Smallpox research in the United States continues and focuses on the development of vaccines, drugs, and diagnostic tests to protect people against smallpox in the event that it is used as an agent of bioterrorism.

What is Smallpox?

Before smallpox was eradicated, it was a serious infectious disease caused by the variola virus. It was contagious—meaning, it spread from one person to another. People who had smallpox had a fever and a distinctive, progressive skin rash.

Most people with smallpox recovered, but about 3 out of every 10 people with the disease died. Many smallpox survivors have permanent scars over large areas of their body, especially their faces. Some are left blind.

Thanks to the success of vaccination, smallpox was eradicated, and no cases of naturally occurring smallpox have happened since 1977. The last natural outbreak of smallpox in the United States occurred in 1949.

Signs and Symptoms
A person with smallpox goes through several stages as the disease progresses. Each stage has its own signs and symptoms.

1.Incubation Period collapsed
This stage can last anywhere from 7 to 19 days (although the average length is 10 to 14 days).

Contagious? No

The incubation period is the length of time the virus is in a person’s body before they look or feel sick. During this period, a person usually has no symptoms and may feel fine.

2.Initial Symptoms collapsed

This stage lasts anywhere from 2 to 4 days.

Contagious? Sometimes. Smallpox may be contagious during this phase, but is most contagious during the next 2 stages (early rash and pustular rash and scabs).

The first symptoms include:

High fever
Head and body aches
Sometimes vomiting

At this time, people are usually too sick to carry on their normal activities.

3.Early Rash collapsed
This stage lasts about 4 days.

Contagious? Yes. At this time, the person is most contagious.

A rash starts as small red spots on the tongue and in the mouth. These spots change into sores that break open and spread large amounts of the virus into the mouth and throat. The person continues to have a fever.

Once the sores in the mouth start breaking down, a rash appears on the skin, starting on the face and spreading to the arms and legs, and then to the hands and feet. Usually, it spreads to all parts of the body within 24 hours. As this rash appears, the fever begins to decline, and the person may start to feel better.

By the fourth day, the skin sores fill with a thick, opaque fluid and often have a dent in the center.

Once the skin sores fill with fluid, the fever may rise again and remain high until scabs form over the bumps.
4.Pustular Rash and Scabs collapsed
This stage lasts about 10 days.

Contagious? Yes

The sores become pustules (sharply raised, usually round and firm to the touch, like peas under the skin).

After about 5 days, the pustules begin to form a crust and then scab.

By the end of the second week after the rash appears, most of the sores have scabbed over.
5.Scabs Fall Off collapsed
This stage lasts about 6 days.

Contagious? Yes

The scabs begin to fall off, leaving marks on the skin.

Three weeks after the rash appears, most scabs will have fallen off.

6.No Scabs

Contagious? No.

Four weeks after the rash appears, all scabs should have fallen off. Once all scabs have fallen off, the person is no longer contagious.

Prevention and Treatment

There is no proven treatment for smallpox disease, but some antiviral drugs may help treat it or prevent it from getting worse. There also is a vaccine to protect people from smallpox. If there were a smallpox outbreak, health officials would use the smallpox vaccine to control it.
Smallpox Vaccine

Smallpox can be prevented by the smallpox vaccine.

If you get the vaccine:

Before contact with the virus, the vaccine can protect you from getting sick.
Within 3 days of being exposed to the virus, the vaccine might protect you from getting the disease. If you still get the disease, you might get much less sick than an unvaccinated person would.
Within 4 to 7 days of being exposed to the virus, the vaccine likely gives you some protection from the disease. If you still get the disease, you might not get as sick as an unvaccinated person would.

Once you have developed the smallpox rash, the vaccine will not protect you.

Currently, the smallpox vaccine is not available to the general public because smallpox has been eradicated, and the virus no longer exists in nature. However, there is enough smallpox vaccine stockpiled to vaccinate every person in the United States if a smallpox outbreak were to occur.

Antiviral Drugs

In laboratory tests, Tecovirimat has been shown to be effective against the virus that causes smallpox. In laboratory settings this drug was effective in treating animals which had diseases similar to smallpox. Tecovirimat has not been tested in people who are sick with smallpox, but it has been given to healthy people. Test results showed that it is safe and causes only minor side effects.
In laboratory tests, Cidofovir and Brincidofovir have been shown to be effective against the virus that causes smallpox. In laboratory settings this drug was effective in treating animals which had diseases similar to smallpox. Cidofovir and Brincidofovir have not been tested in people who are sick with smallpox, but they have been tested in healthy people and in those with other viral illnesses. Test results indicate that Brincidofovir may cause fewer side effects than Cidofovir, which can be toxic to kidneys.
Because these drugs were not tested in people sick with smallpox, it is not known if a person with smallpox would benefit from treatment with them. However, their use may be considered if there ever is an outbreak of smallpox.
Tecovirimat and Cidofovir are currently stockpiled by CDC’s Strategic National Stockpile, which has medicine and medical supplies to protect the American public if there is a public health emergency, including one involving smallpox.