About smallpox virus

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. Smallpox sores covered the body.

What is Smallpox? Signs and Symptoms. Prevention and Treatment. History of Smallpox. Vaccine Basics. For Clinicians. Although similar in name and in the formation of a rash, blisters, and scabs, variola belongs to a different virus family than the virus that causes the common childhood illness chicken pox.

Variola is a member of the Poxvirus family of viruses. A close relative of variola within the Poxvirus family, called vaccinia, does not cause smallpox and is used as a vaccine for smallpox in fact, the word vaccine comes from vaccinia virus. Vaccinia is also used in the laboratory to study this type of virus, because it is less hazardous to work with than the smallpox virus.

A virus related to variola called monkeypox virus recently made headlines when an outbreak occurred in the Midwestern region of the United States in This disease, also characterized by a rash and blisters, was the first monkeypox outbreak in the Western Hemisphere. Monkeypox virus sickened about 70 people. The cause was traced to prairie dogs that had been infected by imported African rodents at a pet distribution center. Fortunately, this disease was not as deadly as smallpox.

People generally become infected with the smallpox virus by breathing in virus droplets following exposure to infected individuals or by direct contact with infected fluids or contaminated objects. An unusual property of the smallpox virus is that it only infects humans and not animals and insects this property was instrumental in the eradication of smallpox.

After exposure to the virus, it usually takes one to two weeks before a person becomes ill and a rash and fever develop. At this point, the person is highly contagious and remains contagious until all scabs fall off after about three weeks. People who recover from the infection are often left with permanent scars and sometimes blindness. By some estimates, smallpox has been responsible for more deaths over the centuries than all other infectious diseases combined.

A worldwide immunization program was instituted decades ago and has led to the elimination of smallpox as a human health threat. This has been one of the greatest success stories in medicine. In the United States, the last confirmed case of smallpox occurred in , and worldwide the last recorded case of naturally occurring smallpox occurred in Somalia in