What type of virus causes smallpox

Smallpox is an extremely contagious and deadly virus for which there is no known cure. The last known case occurred in the United States in and due to worldwide vaccination programs, this disease has been completely eradicated.

Smallpox is also known as variola. Since the time of ancient Egypt, smallpox has proven to be one of the most devastating diseases to humankind. Widespread smallpox epidemics and huge death tolls fill the pages of our history books. The first smallpox vaccine was created in However, the disease continued to infect and kill people on a widespread basis for another years.

The last known natural case occurred in in Somalia. By , the WHO declared that smallpox had been completely eradicated, although government and health agencies still have stashes of smallpox virus for research purposes. People no longer receive routine smallpox vaccinations. The smallpox vaccine can have potentially fatal side effects, so only the people who are at high risk of exposure get the vaccine.

Historical accounts show that when someone was infected with the smallpox virus, they had no symptoms for between seven and 17 days. However, once the incubation period or virus development phase was over, the following flu-like symptoms occurred:.

These symptoms would go away within two to three days. Thanks to the success of vaccination, smallpox was eradicated, and no cases of naturally occurring smallpox have happened since The last natural outbreak of smallpox in the United States occurred in Section Navigation.

Facebook Twitter LinkedIn Syndicate. One vaccine ACAM uses a live virus that's related to smallpox, and it can occasionally cause serious complications, such as infections affecting the heart or brain. That's why it's not recommended that everyone be vaccinated at this time. The potential risks of the vaccine outweigh the benefits, in the absence of an actual smallpox outbreak.

A second vaccine, a modified vaccinia Ankara vaccine Jynneos , has been found to be safe, and it can be used in people who aren't able to take ACAM, who have weakened immune systems or who have skin disorders.

Immunity or partial immunity after a smallpox vaccine may last up to 10 years, and 20 years with revaccination. If an outbreak ever occurred, people who were vaccinated as children would still likely receive a new vaccination after direct exposure to someone with the virus.

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Overview Smallpox is a contagious, disfiguring and often deadly disease that has affected humans for thousands of years. Smallpox Open pop-up dialog box Close. Smallpox These are smallpox lesions on the skin of the trunk.

Request an Appointment at Mayo Clinic. Share on: Facebook Twitter. By the fourth day of the rash, the spots transform into sores that fill with a thick, opaque fluid and have a dent in the center.

The crater-like sores turn into pustules pus-filled lesions , becoming sharply raised, round, and firm to the touch. These pustules may break open, oozing and becoming bloody. After about five days, the pustules begin to form a crust and then scab over. Most sores reach this stage by the end of the second week of the rash.

The scabs fall off after about one more week, leaving deep pockmarks. Smallpox is caused by the variola virus, which, along with the vaccinia virus, monkeypox virus , and cowpox virus, belongs to the genus Orthopoxvirus. There are two species of variola virus — Variola major and Variola minor.

The first can lead to life-threatening illness, while the second rarely results in death. Humans are the only known carriers of the variola virus. Other Orthopoxvirus viruses are normally transmitted to humans from infected animals.

Many illnesses can cause rashes. But it's highly unlikely that a person with a rash has smallpox. Minor diagnostic criteria lower likelihood include:.

Laboratory tests can rule out other potential diagnoses, such as chicken pox, and confirm a smallpox diagnosis. Though both smallpox and chicken pox cause fever and rash, the two diseases are not the same. Chicken pox is caused by the varicella zoster virus, a type of alpha herpesvirus not belonging to the Orthopoxvirus genus.

Though chicken pox can sometimes cause serious complications, the illness is often mild. Chicken pox rash often develops soon after other symptoms begin if there are any and looks like small blisters; the itchy lesions develop one after another, rather than all at once in a single area; and the lesions change rapidly, usually forming scabs within 24 hours.

Smallpox has an average incubation period of 10 to 14 days, during which the person has no symptoms. Initial symptoms last for two to four days and typically include high fever, headaches and body aches, and sometimes vomiting. The person may be contagious during this phase. A person is most contagious over the next four days, when a red rash appears and spreads, then turns into fluid-filled sores. It takes about six days for the scabs to fall off. At this point the person is no longer contagious.

In the past, smallpox treatment focused on relieving symptoms and preventing the spread of the disease by isolating the patient until all the smallpox scabs fell off. In , the U. The drug works by inhibiting the activity of a protein called p37, which ultimately prevents viral particles from leaving an infected cell and spreading to other cells. Research shows that tecovirimat is effective against the variola virus in laboratory settings in cell cultures and can treat diseases similar to smallpox in animals.

Studies also show tecovirimat is safe, with the most frequent side effects being headache, nausea, and abdominal pain. But since the drug was developed after the eradication of smallpox, it hasn't been tested on human subjects, causing some uncertainty about how well it would work in the unlikely event of an outbreak.

Other studies have shown that the antiviral drugs cidofovir currently used to treat an eye infection called cytomegalovirus retinitis in people with AIDS and brincidofovir an experimental drug also used to treat cytomegalovirus retinitis as well as adenovirus are effective against smallpox in lab settings and can treat smallpox-related diseases in animals.

Neither cidofovir nor brincidofovir have been tested on people with smallpox. Scientists continue to study the drugs' effectiveness and toxicity.

The CDC has stockpiles of tecovirimat and cidofovir in case of a public-health emergency. Healthcare workers no longer routinely administer smallpox vaccines to the general public. The CDC recommends smallpox vaccination only for laboratory researchers who study the variola virus or its close relatives. Still, the CDC has stockpiles of smallpox vaccine — enough to give one to every person in the United States if necessary.

The original smallpox vaccine contains live vaccinia virus, which is in the same Orthopoxvirus genus as the variola virus but causes a less severe illness.

Exposure to the vaccinia virus prompts the immune system to produce antibodies that are also effective against the variola virus. This method of gaining smallpox immunity was first developed by the English doctor Edward Jenner.

In , after observing that milkmaids who got cowpox never developed smallpox, he took material from a cowpox sore and inoculated it into the hand of his gardener's 9-year-old son. Then he repeatedly exposed the boy to the variola virus — and the child did not develop smallpox. Sometime in the s, the virus used to make the smallpox vaccine switched from cowpox to vaccinia.

The smallpox vaccine prevents infection in 95 percent of those who receive it, and is also able to prevent or lessen infection when given within a few days of exposure to variola virus. Since the eradication of smallpox, scientists have developed a newer version of the vaccine that uses attenuated weakened viral strains.

Unlike most other vaccines, the smallpox vaccine does not involve an injection or "shot. A doctor uses the needle to prick the skin usually in the upper arm multiple times in a few seconds. A successful vaccination causes a red and itchy lesion to develop at the vaccine site within three to four days.