Smallpox

Topic Overview

What is smallpox?

Smallpox is a contagious infection caused by the variola virus. Smallpox can be deadly, so if an outbreak happens, it is vital to stay away from infected people. Get vaccinated if you have been around someone who has smallpox. And if you have symptoms, seek medical care.

The telltale signs of smallpox are severe illness with a high fever, then a body rash. Symptoms appear about 12 days after the person is infected.

Before there was a vaccine, smallpox used to cause death all around the world. Thanks to widespread use of the vaccine, the last natural case of smallpox occurred in 1977. And in 1980 the World Health Organization (WHO) declared that the spread of smallpox was stopped and that the disease had been wiped out.

Because there is a slight risk of serious reactions and even death from the smallpox vaccine, routine smallpox immunization ended in the United States in 1972.

Smallpox virus is known to exist in labs at the Centers for Disease Control and Prevention (CDC) in the U.S. and at the Institute of Virus Preparations in Siberia, Russia. But it may also be in other labs. Some people worry that terrorists could release the virus and spread smallpox to many people.

What are the symptoms?

The first symptoms of smallpox include a high fever, fatigue, a headache, and a backache. It takes about 12 days for these symptoms to show. Then after 2 to 3 days of illness, a flat, red rash appears. It usually starts on the face and upper arms, and then it spreads all over your body. Over the next 2 to 3 weeks, the flat, red spots become firm and dome-shaped and fill with pus. Then they scab over. Scabs fall off 3 to 4 weeks after the rash first appears, and they leave pitted scars.

You may mistake a severe chickenpox rash for a smallpox rash at first. But different viruses cause these illnesses.

How is smallpox spread?

Smallpox is contagious. It can be passed from one person to another through coughing, sneezing, or breathing, or by contact with the scabs or the fluid from blisters. It can even spread from an infected person's personal items and bedding. Smallpox is easiest to spread during the first week of the rash. As scabs form, the person is less contagious. But a person can spread the virus from the time the rash first appears until all scabs have fallen off.

If a terrorist were to release a small amount of the virus into the air, it is possible that it could spread among a large number of people. The virus could survive and infect people for 6 to 24 hours, depending on the weather.¹

People who get this disease must stay away from others to help prevent it from spreading. If there has been a smallpox outbreak and you think you might have been exposed, call your local health department or 911 . Do not go directly to a health facility, because you could pass the disease to other people.

How is smallpox diagnosed?

If a doctor suspected a case of smallpox, a blood test would be needed to confirm the diagnosis. A confirmed case of smallpox would be considered a worldwide health emergency. In the U.S., state and federal health officials would quickly take action. They would keep anyone who might have been exposed away from others.

If a smallpox outbreak had been confirmed, a doctor in the outbreak area could diagnose smallpox without a lab test. The doctor would look at the rash and ask about symptoms and possible exposure to the disease.

How is it treated?

There is no known cure for smallpox. Treatment includes drinking plenty of fluids and taking medicines to control pain and fever.

To prevent the spread of the virus, an infected person must be kept away from other people until he or she is no longer contagious.

Can smallpox infection be prevented?

People who have survived smallpox cannot get it again.

Also, there is a smallpox vaccine. It has vaccinia virus in it, which is like the smallpox virus but safer. If you get the shot before you've been exposed to smallpox, it will likely protect you for at least 3 to 5 years. And having a second shot later can protect you for an even longer period of time.

The shot works even if you don't get it in advance. Most people who get the smallpox shot within 3 days after they've been exposed to the virus will have no symptoms or will have symptoms that aren't as severe. Getting a shot 4 to 7 days after exposure may also help.²

In the past, when a smallpox infection was diagnosed, infected people were kept away from others to prevent the spread of infection. Everyone who might have been exposed to the virus was then vaccinated. This practice, called ring vaccination, played a key role in wiping out smallpox. Many experts think it would be better to carry out ring vaccination before mass vaccination if there were a case today.

Because there are risks of a serious reaction from the vaccine, routine smallpox immunization doesn't occur. All children and most adults in the U.S. today have the chance of getting infected if they were exposed to the smallpox virus.

Since the September 2001 terrorist attacks on the U.S., more vaccine has been made. The U.S. government has enough smallpox vaccine for all Americans in case of an outbreak.²

Frequently Asked Questions

Symptoms

The incubation period for smallpox is about 12 days. But symptoms can develop as soon as 7 days or as long as 19 days after exposure.

During the first 2 to 3 days of illness, smallpox causes symptoms that affect the whole body (systemic symptoms), including:

• High fever, often rising to more than 104 °F (40 °C), then dropping over 2 to 3 days.
• Extreme lack of energy (lethargy).
• Severe headache.
• Severe backache.
• Severe abdominal pain and vomiting (in some cases).
• Delirium (in some cases).
• Seizures in some children.

Rash development and progression

After 2 to 3 days of severe illness, the smallpox rash appears in the mouth and throat, but it may not be noticeable. About 24 hours later, a rash appears on the face and arms. During the first week of rash, a large amount of the smallpox (variola) virus is in the saliva, making the infected person's saliva highly contagious. Spreading the virus through coughing and sneezing is most likely at this time.

Smallpox lesions appear on the skin over a 1- to 2-day period. Unlike a chickenpox rash, all smallpox lesions on the same part of the body change appearance at the same time, about every 1 to 2 days. Over a 2- to 3-week period, the rash progresses through the following stages:³

• Macules. Tiny flat, red spots usually appear first in the throat and mouth. These may go unnoticed until spots also show up on the face or arms. The rash then spreads to the rest of the body, becoming most concentrated on the face, feet, and hands.
• Papules. The red spots become bumpy, growing to about 0.1 in. (2.5 mm) in diameter.
• Vesicles. The lesions fill with fluid, growing to about 0.2 in. (5.1 mm) in diameter.
• Pustules. About 4 to 7 days after the rash appears, the lesions become firm, dome-shaped, whitish, and pus-filled, growing slightly larger with depressed centers. This stage lasts from 5 to 8 days.
• Crusts. By the second week of rash, the pustules crust over and turn into scabs. Scabs fall off 3 to 4 weeks after the rash first appears, leaving pitted scars.

Although a severe chickenpox infection may be mistaken for smallpox, there are numerous differences between chickenpox and smallpox . For example, the smallpox rash usually first appears in the throat and mouth or on the arms, and then moves to the torso. The chickenpox rash usually first appears on the torso, and pustules in many different stages are present at the same time (while some are new, others are crusting over).

Death

Up to 30% of people infected with smallpox die.⁴ The infection can overwhelm the body's defenses, leading to organ failure. But all cases of smallpox took place before modern medical advances. So it is possible that less people would die if a smallpox outbreak were to occur today.

When to Call a Doctor

In the past, severe chickenpox was often mistaken for smallpox. But there are numerous differences between chickenpox and smallpox . For example, the smallpox rash usually first appears in the throat and mouth or on the arms, and then moves to the torso. The chickenpox rash usually first appears on the torso.

• If a smallpox outbreak has occurred and you are concerned that you have symptoms of smallpox infection, call your local health department or 911 immediately for instructions. Because of the risk of spreading infection, do not go directly to a medical facility.

• If a smallpox outbreak has not occurred but you are concerned that you have been exposed and have symptoms of smallpox infection, call your doctor immediately to discuss your symptoms.

Exams and Tests

A suspected first case of smallpox is considered an international health emergency. Specialized laboratory testing is necessary to confirm a suspected smallpox infection.

• Specially trained and vaccinated doctors take fluid samples from the person's mouth or from the suspected smallpox lesions.
• The sealed samples are shipped to the Centers for Disease Control and Prevention (CDC) or another designated laboratory that is equipped to handle the variola virus.

In the laboratory, variola virus can be quickly identified using a combination of:

• An electron microscope to examine the appearance of the virus.
• Viral culture.
• Various tests to identify the virus's genetic material, or DNA.

If a smallpox (variola) outbreak is already documented, a physical exam and history of symptoms and exposure may be sufficient for your doctor to diagnose smallpox.

Treatment Overview

There is no cure for smallpox. After symptoms start, treatment consists of supportive medical care, including giving the person fluids to prevent dehydration and medicines to control pain and fever. New treatments, such as medicines that work well for other viral diseases, may also be tried.

Isolating the person until all the scabs have fallen off-about 3 to 4 weeks after the rash first appears-is necessary to prevent spreading the infection to others.

Prevention

Vaccination

The smallpox vaccine (What is a PDF document?) is the only known way to prevent smallpox if a person is exposed. When given within 3 days of exposure, the vaccine can prevent or greatly reduce the severity of smallpox symptoms in most people. Getting a shot 4 to 7 days after exposure may also help.² The smallpox vaccine is made from the vaccinia virus, which is similar to variola virus, but safer. The vaccinia virus does not cause smallpox illness.

In the past, the smallpox vaccine was used to get rid of smallpox infection worldwide using:

• Ring vaccination of all people who were or may have been exposed to smallpox.
• Mass vaccination, to prevent infection of an entire population. Before 1972, all children in the United States were vaccinated before they started school. Routine smallpox vaccination ended in 1972 when smallpox risk in the United States became minimal.

Many disease-control experts think ring vaccination would be better than mass vaccination if there were a documented smallpox case today.

In the U.S., vaccination is being offered to medical personnel and other people who would be exposed to the virus if an outbreak of smallpox occurred (first responders). The smallpox vaccine does not give lifelong protection, and there are risks of a serious reaction from it. That's why routine smallpox immunization does not take place at this time. Health workers should always wash their hands or use a hand sanitizer after any contact with the vaccine or with the vaccination site.

The Centers for Disease Control and Prevention (CDC) has guidelines about who should not receive the vaccine. Those at increased risk of having complications from the vaccine include:

• Pregnant women, because of the risk of infecting the unborn baby.
• Breast-feeding women, because of the risk of infecting the baby.
• People with skin conditions, such as active or healed eczema.
• Babies younger than 1 year.
• People who have an impaired immune system, such as those infected with human immunodeficiency virus (HIV) or cancer.
• People with serious, life-threatening allergies (anaphylaxis) to the antibiotics polymyxin B, streptomycin, tetracycline, or neomycin.

If you have heart problems or three or more risk factors for heart disease, you should not be vaccinated until more is known about a possible relationship between the smallpox vaccine and heart problems, including heart attack.

But if you are directly exposed to smallpox, you should be vaccinated even if you fall into one of these groups.⁵ In such a situation, the risk of death from smallpox is greater than the risk of having a harmful reaction to the vaccine.

Isolation and infection control

People who get this disease must stay away from others to help prevent it from spreading. Smallpox spreads by:

• Face-to-face contact with someone who has smallpox (usually someone who already has a smallpox rash).
• Direct contact with infected bodily fluids or an object such as bedding or clothing that has the virus on it.
• Exposure to smallpox virus released in the air (aerosol).

Ideally, an infected person would be isolated and cared for in a medical facility to prevent the spread of infection. Also, a person who may have been exposed should be vaccinated and isolated until it is certain he or she does not have the disease.

Clothing and bedding that have been in contact with an infected person should be washed in hot water with bleach. Hospital-strength disinfectants, such as hypochlorite and quaternary ammonia, can also kill the virus.

Scabs from smallpox lesions may contain the variola virus and could be infectious for months. They should be handled and disposed of as infectious medical waste.

Smallpox and Bioterrorism

Because of the recent increase in global terrorist activity, governments around the world have become concerned that terrorists might use smallpox as a weapon. If a terrorist were to release a small amount of the virus into the air, it is possible that it could spread among a large number of people. The virus could survive and infect people for 6 to 24 hours, depending on the weather.

In early 2001, the United States government increased its preparedness for a smallpox outbreak and took steps to expand its vaccine stockpile. The U.S. has enough smallpox vaccine to vaccinate Americans in an emergency.²

Smallpox (vaccinia) vaccine (What is a PDF document?) is recommended for laboratory personnel who work with the vaccinia virus, for members of smallpox response teams, and for certain members of the military. Vaccination is not currently recommended for the public. For accurate, up-to-date information, visit the Centers for Disease Control and Prevention (CDC) Web site at www.bt.cdc.gov/agent/smallpox.

Special-risk populations

Certain people have a higher risk of having complications from the vaccine and should not be vaccinated unless they are exposed to smallpox. These include:

• Pregnant women, because of the risk of infecting the fetus.
• Breast-feeding women, because of the risk of infecting the baby.
• People with skin conditions, such as active or healed eczema.
• Children younger than age 1.
• People who have an impaired immune system.
• People with serious, life-threatening allergies (anaphylaxis) to the antibiotics polymyxin B, streptomycin, tetracycline, or neomycin.
• People who have household contact with someone who has an impaired immune system, is pregnant, or has certain skin conditions, such as active or healed eczema.

If you have heart problems or three or more risk factors for heart disease, you should not be vaccinated until more is known about a possible relationship between the smallpox vaccine and heart problems, including heart attack.

But if you are directly exposed to smallpox, you should be vaccinated even if you fall into one of these groups.⁵ In such a situation, the risk of death from smallpox is greater than the risk of having a harmful reaction to the vaccine.

Helpful Resources

To learn more about smallpox, contact your local health department or the Centers for Disease Control and Prevention. For accurate, up-to-date information, visit the Centers for Disease Control and Prevention (CDC) Web site at www.bt.cdc.gov/agent/smallpox.

Other Places To Get Help

Organizations

Related Information

• Chickenpox (Varicella)
• Immunizations
• Terrorism and Other Public Health Threats

References

Citations

1. Henderson DA, et al. (1999). Smallpox as a biological weapon: Medical and public health management. JAMA, 281(22): 2127-2137.

2. Centers for Disease Control and Prevention (2007). Smallpox fact sheet: Vaccine overview. Available online: http://www.bt.cdc.gov/agent/smallpox/vaccination/facts.asp.

3. Breman JG, Henderson DA (2002). Diagnosis and management of smallpox. New England Journal of Medicine, 346(17): 1300-1308.

4. Rotz LD, et al. (2005). Smallpox and bioterrorism. In GL Mandell et al., eds., Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases, 6th ed., vol. 2, pp. 3612-3617. Philadelphia: Elsevier Churchill Livingstone.

5. Centers for Disease Control and Prevention (2001). Vaccinia (smallpox) vaccine recommendations of the Advisory Committee on Immunization Practices (ACIP). MMWR, 50(RR-10): 1-25.

Other Works Consulted

• American Academy of Pediatrics (2006). Smallpox (variola). In LK Pickering, ed., Red Book: 2006 Report of the Committee on Infectious Diseases, 27th ed., pp. 591-595. Elk Grove Village, IL: American Academy of Pediatrics.

• Centers for Disease Control and Prevention (2004). Smallpox fact sheet: Smallpox overview. Available online: http://www.bt.cdc.gov/agent/smallpox/overview/overview.pdf.

• Cherry JD (2004). Smallpox (variola virus). In RD Feigin et al., eds., Textbook of Pediatric Infectious Diseases, 5th ed., pp. 1972-1977. Philadelphia: Saunders.

• Damon I (2005). Orthopoxviruses: Vaccinia (smallpox vaccine), variola (smallpox), monkeypox, and cowpox. In GL Mandell et al., eds., Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases, 6th ed., vol. 2, pp. 1742-1751. Philadelphia: Elsevier Churchill Livingstone.

• Henderson DA, et al. (2008). Smallpox and vaccinia. In SA Plotkin et al., eds., Vaccines, 5th ed., pp.773-803. Philadelphia: Saunders Elsevier.

• Hirsch MS (2007). Measles, mumps, rubella, parvovirus, and poxvirus. In DC Dale, DD Federman, eds., ACP Medicine, section 7, chap. 29. New York: WebMD.

• Lane CH, Fauci AS (2008). Bioterrorism and clinical medicine: Microbial bioterrorism. In AS Fauci et al., eds., Harrison's Principles of Internal Medicine, 17th ed., pp. 1348-1349. New York: McGraw-Hill.

• National Guideline Clearinghouse (2008). Guideline synthesis: Smallpox vaccination. Available online: http://www.guideline.gov/Compare/comparison.aspx?file=smallpox4.inc.

• Weiss MM, et al. (2004). Rethinking smallpox. Clinical Infectious Disease, 39(11): 1688-1673.

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