Causes

Smallpox was once found throughout the world, causing illness and death wherever it occurred. It mainly affected children and young adults. Family members often infected each other.

Smallpox spreads easily from one person to another from saliva droplets. It may also be spread from bed sheets and clothing. It is most contagious during the first week of the infection. It may continue to be contagious until the scabs from the rash fall off.

Researchers believe that the smallpox infection might be able to stay alive (under the right conditions) for as long as 24 hours. In unfavorable conditions, the virus may only remain alive for 6 hours.

People were once vaccinated against this disease. However, the United States stopped giving the smallpox vaccine in 1972. In 1980, the World Health Organization (WHO) recommended that all countries stop vaccinating for smallpox.

There are two forms of smallpox:

• Variola major is a serious illness that can be life threatening in people who have not been vaccinated
• Variola minor is a milder infection that rarely causes death

A massive program by the World Health Organization (WHO) wiped out all known smallpox viruses from the world in the 1970s, except for a few samples saved for government research. Researchers continue to debate whether or not to kill the last remaining samples of the virus, or to preserve it in case there may be some future reason to study it.

You are more likely to develop smallpox if you:

• Are a laboratory worker who handles the virus (rare)
• Are in a location where the virus was released as a biological weapon

It is unknown how long past vaccinations stay effective. People who received the vaccine many years ago may no longer be fully protected against the virus.

THE RISK OF TERRORISM

There is a concern that the smallpox virus could be intentionally spread through a terrorism attack. The virus could be deliberately spread in spray (aerosal) form.

Symptoms

Symptoms usually occur about 12 - 14 days after you have been infected with the virus. They may include:

• Backache
• Delirium
• Diarrhea
• Excessive bleeding
• Fatigue
• High fever
• Malaise
• Raised pink rash -- turns into sores that become crusty on day 8 or 9
• Severe headache
• Vomiting

Exams and Tests

Tests include:

• DIC panel
• Platelet count
• White blood cell count

Special laboratory tests can be used to identify the virus.

Treatment

If athe smallpox vaccine is given within 1-4 days after a person is exposed to the disease, it may prevent illness or make the illness less severe. Once symptoms have started, treatment is limited.

There is no drug specifically for treating smallpox. Sometimes antibiotics are given for infections that may occur in people who have smallpox. Taking antibodies against a disease similar to smallpox (vaccinia immune globulin) may help shorten the duration of the disease.

People who have been diagnosed with smallpox and everyone they have come into close contact with need to be isolated immediately. They need to receive the vaccine and be monitored.

Emergency measures would need to be taken immediately to protect the general population. Health officials would follow the recommended guidelines from the CDC and other federal and local health agencies.

Outlook (Prognosis)

In the past, this was a major illness with the risk of death as high as 30%.

Possible Complications

• Arthritis and bone infections
• Brain swelling (encephalitis)
• Death
• Eye infections
• Pneumonia
• Scarring
• Severe bleeding
• Skin infections (from the sores)

When to Contact a Medical Professional

If you think you may have been exposed to smallpox, contact your health care provider immediately. Because smallpox has been wiped out this would be very unlikely, unless you have worked with the virus in a laboratory or there has been an act of bioterrorism.

Prevention

Many people were vaccinated against smallpox in the past. The vaccine is no longer given to the general public because the virus has been wiped out. The possible complications and costs of the vaccine outweigh the benefits of taking it.

If the vaccine needs to be given to control an outbreak, it can have a small risk of complications. Some complications are mild, such as rashes. Others are more serious.

Only military personnel, health care workers, and emergency responders may receive the vaccine today. Smallpox vaccination policies and practices are currently being reviewed.

Alternative Names

Variola - major and minor; Variola

References

Damon, Inger. Orthopoxviruses: vaccinia (smallpox vaccine), variola (smallpox), monkeypox, and cowpox. In: Mandell GL, Bennett JE, Dolin R, eds. Principles and Practice of Infectious Diseases. 6th ed. Philadelphia, Pa: Churchill Livingstone Elsevier;2005:chap 129.

Frequently asked questions about smallpox vaccine. CDC Emergency preparedness and response. Accessed February 7, 2007.

Update Date: 4/23/2012

Reviewed by: Jatin M. Vyas, MD, PhD, Assistant Professor in Medicine, Harvard Medical School; Assistant in Medicine, Division of Infectious Disease, Department of Medicine, Massachusetts General Hospital. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.