Smallpox is a disease that has been successfully eradicated - the last naturally occurring case of smallpox occurred in Somalia in 1977. With recent world events and the biological warfare threat, this conquered disease has again risen to the forefront of public health. Smallpox is a highly contagious skin disease that can result in death.
Smallpox - Variola Virus Infection
Smallpox is caused by the variola virus, a brick-shaped DNA virus in the orthopoxvirus genus. The variola virus is among the largest of all animal viruses and can be seen with a light microscope. The variola virus initially infects the cells in the respiratory tract, then spreads to lymph nodes. The virus enters the bloodstream about 3-4 days after the initial infection.
Spread of Smallpox
Smallpox is most easily spread from person-to-person by the inhalation of respiratory droplets. Smallpox can also be spread by contact with contaminated clothing or bed linens used by an infected person because the virus can survive on objects for up to one week. Smallpox is not spread by insects or animals.
First Symptoms of Smallpox
The incubation period of smallpox, the time from when the virus enters the body to the beginning of symptoms, is 12 days. The first symptoms of smallpox resemble those of any acute viral illness - high fever, muscle aches, fatigue, headaches, and sometimes vomiting.
Smallpox Rash
The smallpox rash develops 2-4 days after the systemic symptoms. The rash normally starts on the face or in the mouth, then spreads to the arms and hands, followed by the legs and trunk. The appearance of the rash starts as reddish raised bumps (maculopapular rash). The bumps turn into blisters (vesicles), and then pustules. The pustules dry, scab over, and then fall off leaving a pitted scar in the survivors.
Smallpox Deaths
In 30% of unvaccinated people, smallpox results in death 1 to 2 weeks after infection as the bloodstream becomes overloaded with the virus.
Smallpox Contagion
A person is most contagious when the rash starts and remains contagious until the last scab falls off. Sometimes a person is contagious when the fever starts, before the appearance of the rash.
Diagnosis of Smallpox
Immediate isolation is necessary if the diagnosis of smallpox is considered. The CDC should be contacted and all people who came in contact with the patient should be identified. Smallpox is diagnosed by performing laboratory tests on the fluid from the lesions. An electron microscope can also be used to identify the virus in infected fluid. Blood tests for antibodies can be performed and compared to blood tests for antibodies taken 4 weeks later, but this method has obvious timing drawbacks.
Treatment of Smallpox
There is no known treatment of smallpox. Studies are being performed to determine if certain antiviral drugs will be effective, but this research is still in the early stages. Smallpox can be prevented with vaccination. Vaccination up to 3 days after exposure will prevent smallpox or significantly reduce the symptoms and likelihood of death. Vaccination 4 to 7 days after exposure may still be helpful in reducing symptoms.
Information for this article was taken from
-Polgreen P, Helms C. Immunizations - Vaccines, biological warfare, and bioterrorism. Primary Care Clinics in Office Practice 01-Dec-2001; 28(4): 807-21, vii.
-Diven D. An overview of poxviruses. Journal of the American Academy of Dermatology 01-Jan-2001; 44(1): 1-16.
-Silvers M, Steptoe M. Immunizations - Historical overview of vaccines. Primary Care Clinics in Office Practice 01-Dec-2001; 28(4): 685-95, v.
