Smallpox
Basic Facts
- Scientific name: Variola major;a virus from the Orthopoxvirus family
- A closely related virus, Variola minor,causes a less severe form of illness with less than 1 percent fatality rate.
- Smallpox was a naturally occurring disease that killed an estimated 300 million people in the 20th century.
- Officially eradicated in nature in 1980, smallpox has more recently been of concern as a potential bioterrorism threat.
- The smallpox virus is moderately contagious; direct, face-to-face contact is usually required to spread the disease. Smallpox can also be spread through direct contact with infected body fluids or contaminated objects (e.g., bedding).
- Characterized by skin lesions and high fever, smallpox historically has killed approximately 30 percent of those infected.
- Routine vaccinations in the United States ended in 1972. At present, a large portion of the population is considered vulnerable to infection should a bioterrorism incident occur.
Smallpox as a Weapon
Because it is contagious from person to person and could potentially infect large groups of people, taxing the healthcare systems of a community, smallpox would be an attractive weapon for terrorists. It would most likely be delivered in an aerosol form.
- The smallpox virus could be disseminated into the air as a fine spray or powder and could infect large numbers of people.
- In aerosol form, the smallpox virus may be infectious for 24 hours before degrading. Heat and sunlight (UV exposure) may destroy the virus within hours.
- Terrorists could possibly use smallpox virus samples to intentionally infect a few people, possibly themselves, with the intention of infecting others. However, it is doubtful that any one individual would succeed in infecting more than a few others. By the time that these individuals were contagious, they would be very obviously seriously ill.
What We Don't Know About Smallpox as a Weapon
Experts do not know if the smallpox virus in a weaponized form would be as contagious as the disease was before it was eradicated.
Identifying an Attack
Because smallpox has been eradicated worldwide, even one case of smallpox would be considered a probable terrorist attack.
The first sign of an attack would most likely be victims becoming ill, usually between seven and 17 days after exposure.
A properly disseminated aerosol cloud of the smallpox virus would be invisible, odorless, and extremely hard to detect.
Smallpox Illness
Exposure:
- The incubation period is typically seven to 17 days following exposure.
- Infection usually occurs only when a susceptible person is in face-to-face contact with someone who has the virus and is ill with fever and a rash of round lesions.
- The virus is usually spread by droplets; however, having it spread by aerosol or contaminated objects (e.g., bedding) is also possible.
- Smallpox is not known to be transmitted by insects or animals.
Symptoms:
- Initial symptoms of smallpox may include high fever, fatigue, headache, and backache.
- Typically, people with smallpox are not contagious until lesions start appearing and they are obviously ill.
- Two to three days after the onset of symptoms: A rash of round lesions develops on the face, arms, and legs. At the same time, lesions in the mouth are also present and release large amounts of the virus into the saliva.
- Seven days after the onset of symptoms: The lesions become small blisters and by the seventh day are filled with pus.
- Twelve days after the onset of symptoms: Lesions begin to crust over. Severe abdominal pain and delirium can occur in the later stages of the disease.
- Three to four weeks after the onset of symptoms: Scabs develop and fall off. A patient who survives is no longer contagious after the final scab falls off.
Recovery/Mortality Rate:
- Death is likely in one third of all smallpox cases, usually during the first or second week of illness.
- Of those who recover, 65 to 85 percent are marked with deep-pitted scars.
- Some who recover may be permanently blind.
Diagnosis
Physicians have not seen cases of smallpox for more than two decades, and making a diagnosis would require familiarity with the disease and its history. However, the Centers for Disease Control and Prevention has worked on educating first responders and emergency room personnel about the signs and symptoms of smallpox.
- Smallpox is most commonly identified by the distinctive rash it causes.
- The rash can sometimes be confused initially with chicken pox.
- The smallpox lesions are painful (as opposed to chicken pox lesions).
- The distribution of smallpox lesions on the body is different from those of chicken pox.
- Patients with smallpox are typically much sicker.
- Testing of the fluid from the lesions can confirm smallpox.
Treatment
There is little that physicians can do, other than giving supportive care, to treat the illness itself; containing a smallpox outbreak becomes the priority once a case is suspected or confirmed. The public health community becomes involved to track down and vaccinate those who may have been exposed to an infected patient and their close contacts (e.g., family). Strict home or hospital isolation of cases is very important; close contacts must be kept under close daily surveillance and isolated if they develop fever.
- Antibiotics are not effective.
- There is no way to fight the virus once patients become sick.
- Patients with smallpox are isolated.
- Patients with smallpox may require intravenous fluids and medication to control fever or pain.
- Secondary bacterial infections of the skin sometimes occur. These can be treated with antibiotics.
- Research is currently underway on the use of the antiviral drug cidofovir as a treatment for smallpox.
Vaccine
After the September 11 attacks, fears that terrorists would use the smallpox virus as a biological weapon led to renewed vaccine production. There is now enough vaccine available in the Strategic National Stockpile for every American in case of an attack.
- The vaccine contains a live virus (vaccinia) which is related to the smallpox virus but entirely different from it; the vaccinia virus is weaker so that people produce antibodies but usually develop only the single pustule at the site of vaccination and, sometimes, a low-grade fever.
- The vaccine provides a high level of immunity from infection for three to five years after vaccination and decreasing immunity thereafter. It is unclear how long the vaccine provides some protection against the disease. If a person is vaccinated again later, immunity lasts even longer.
- However, if a person actually has had smallpox and survives, he or she then has lifelong immunity.
- The vaccine prevents disease in 95 percent of those vaccinated.
- Given within three days after exposure to the smallpox virus, the vaccine will prevent or significantly modify smallpox in the majority of persons. Vaccination four to seven days after exposure most likely offers some protection from disease or may modify the severity of the disease.
- The smallpox vaccine is currently not administered to the general public because:
The likelihood of an attack is not known.
Vaccination can result in complications for several specific groups of people with skin conditions, such as eczema, as well as for people with HIV/AIDS and others with compromised immune systems
Pregnant women, infants under 1 year old, and those taking steroids could also suffer complications
Recent research indicates that people with certain heart conditions should not receive the vaccine (at least until further research is conducted). - The vaccine is effective after one dose, so it could easily be given to many people if a smallpox event or outbreak takes place.
- Vaccination of only those people who might have been exposed to the smallpox virus and their contacts (ring vaccination) was used successfully in the past to eradicate smallpox. However, mass vaccination might be necessary in the aftermath of a terrorist attack.
What We Don't Know About the Smallpox Vaccine
Experts do not know how many of those vaccinated or revaccinated for smallpox before 1972 can still get sick if exposed today.
Prevention
- Place smallpox patients in medical isolation so that they will not spread the virus.
- Take special precautions to ensure that all bedding and clothing of patients are cleaned using bleach and hot water.
- Clean contaminated surfaces with disinfectants, such as bleach or ammonia.
- Within three days, vaccinate people who have come into direct and prolonged face-to-face contact with smallpox patients. Closely watch them for symptoms of smallpox.
- In an aerosol release, widespread decontamination is not necessary, since the airborne virus rapidly blows away from the area and particles die on their own within one to two days.
- Physicians typically use a "ring vaccination" approach, vaccinating the circle of people who may have come in contact with a smallpox patient and the family contacts of this group of people in order to provide a ring of protection from further spread. This approach was successfully used in the past to control outbreaks until smallpox was finally eradicated.
Assessing the Risk
- The smallpox virus has a low availability, as the only two confirmed repositories for the virus are in high-containment laboratories in the United States and Russia. Still, there is concern that some countries may have secretly retained their smallpox samples for bioweapons research and production.
- The smallpox virus is highly stable (can survive for one to two days) in aerosol form.
- Terrorists would have to be moderately skilled to produce the smallpox virus in aerosol form if they could acquire the virus.
- Smallpox is highly lethal because it kills approximately 30 percent of those infected; it is quite contagious and spreads from person to person.
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