What is smallpox?

Causes and Symptoms

The variola virus that causes smallpox is spread through physical contact with infected victims, sometimes through droplets from nasal or oral secretions and sometimes through contact with scabs carried on bedding, towels, clothing, or other fabrics. After exposure to the variola virus, the incubation period ranges from seven to seventeen days. Early symptoms resemble influenza and include headache, muscle ache, and sometimes vomiting. When the characteristic rash appears, the infected person is already seriously ill. In unvaccinated persons not treated with antiviral medications, between 20 and 40 percent of persons infected with classic smallpox (variola major) would be expected to die. Death most often occurs between the fifth and seventh day of illness.

The initial deep-seated rash characteristic of smallpox develops into lesions, which then follow a progressive sequence of fluid-filled vesicles, then pustules, and finally scabs. Lesions often appear first on the face. In contrast to chickenpox, in which “crops” of lesions appear, all smallpox lesions are at the same phase in development. Smallpox cases become contagious when the first lesions appear and remain so until the last scab separates from the skin. After the scabs are completely shed, the recovered smallpox victim is left with characteristic pitted scars over large portions of the body. Some victims are rendered permanently blind as a result of contracting smallpox; men may be left sterile. Survival is generally accompanied by lifetime immunity to further infections.

Treatment and Therapy

Smallpox may be prevented through vaccination. Live vaccinia virus is introduced into the skin tissue of healthy people in an effort to provide immunity against smallpox. The vaccinia virus is very similar to the variola virus that causes smallpox. Live vaccinia virus has been used for smallpox vaccinations since the time of Edward Jenner, the Englishman who pioneered vaccination in the late eighteenth century.

There is no treatment known to cure smallpox, although vaccination may be effective in lessening disease severity when administered within four days of exposure. In the 1970s, methisazone (N-methylisatin beta-thiosemicarbazone), trade name Marboran, was believed to afford some protection when administered early in the incubation period. Isolation of victims, burning all contaminated discharges, concurrent disinfection of the isolation environment, and sterilization of bedclothes and fabrics, combined with quarantine and vaccination of all persons susceptible to smallpox, has been used to contain epidemics in the historical past.

One of the last outbreaks of smallpox in the United States occurred in New York in 1947. To prevent a nationwide outbreak that year, the New York City Board of Health vaccinated about six million people (80 percent of the city’s population) within a four-week period.

The final smallpox outbreak in the United States occurred in the Rio Grande Valley of Texas in 1949. The last case reported in the Western Hemisphere was in Brazil in 1971. Prior to the official “last case” of smallpox observed in human populations in October 1977, international travelers were responsible for introducing the disease into areas where people had not received vaccinations to prevent smallpox. A laboratory accident in England in 1978 caused several cases of smallpox. In 1980, the World Health Organization (WHO) officially declared that smallpox had been eradicated. Major world powers, including the United States and the Soviet Union, maintained stocks of viable smallpox virus for further study.

Perspective and Prospects

There are no natural carriers of smallpox virus; prior to its eradication, it was an endemic urban disease found only in humans, spread as healthy people came into contact with smallpox cases or with fabrics containing scabs shed by smallpox patients.

Following the terrorist attacks on the United States on September 11, 2001, a series of letters containing anthrax spores were sent through the US mail. These letters caused inhalation anthrax, resulting in severe illnesses and several fatalities. Governments became concerned that terrorists would attempt to cause smallpox epidemics. Within the United States, a program was initiated in 2002 to vaccinate “first responder” health professionals in the event of a bioterrorist
attack using smallpox. Few people volunteered for vaccination, but among the outwardly healthy people who were vaccinated, two died unexpectedly from cardiovascular disease. News reports of these deaths made people who were offered vaccination less willing to participate, although subsequent study seemed to indicate that these deaths were not directly attributable to receiving the vaccine.

Few Americans, even those now involved in research on the smallpox virus, have ever seen an active case. If a bioterrorist attack using the smallpox virus were to occur, then medical personnel might have some initial difficulty identifying the disease. The general public would need to be informed about the disease in a manner that would avoid widespread panic and ensure that those exposed were immediately vaccinated and quarantined.

No medication has been approved to treat smallpox. Various antiviral agents had been investigated; the drug cidofovir (Vistide), at that time approved only to treat cytomegalovirus retinitis, was identified by several authorities as a potential agent to treat smallpox. Supportive measures that may be used include fever reducers, pain control medication, intravenous rehydration, and antibiotics to control secondary infections.

A single case of smallpox occurring anywhere in the world at any time in the future would constitute an immediate epidemiological emergency. Smallpox is a “Class 1” internationally quarantinable disease; any cases must be reported immediately to local, state, national, and international health authorities.

The resurgence of interest in smallpox at the start of the twenty-first century brought forth many new ideas about all aspects of the disease and its prevention. In 2003, several researchers noted that the increase in numbers of people infected by human immunodeficiency virus (HIV) corresponded with the decline in smallpox vaccinations worldwide. Laboratory research has since determined that prior infection with the vaccinia virus (through vaccination) may confer some immunity to HIV.

Bibliography:

Baciu, Alina, et al., eds. The Smallpox Vaccination Program: Public Health in an Age of Terrorism. Washington, D.C.: National Academies Press, 2005.

Benenson, Abram S., ed. Control of Communicable Diseases in Man. 16th ed. New York: American Public Health Association, 1995.

Division of Bioterrorism Preparedness and Response. "What You Should Know about a Smallpox Outbreak." Centers for Disease Control and Prevention, March 13, 2009.

Frieden, T., et al. “Cardiac Deaths After a Mass Smallpox Vaccination Campaign—New York City, 1947.” Morbidity and Mortality Weekly Report 52, no. 39 (October 3, 2003): 933–936.

Glynn, Ian, and Jenifer Glynn. The Life and Death of Smallpox. New York: Cambridge University Press, 2004.

Heymann, David L., ed. Control of Communicable Diseases Manual. 19th ed. Washington, D.C.: American Public Health Association, 2008.

"Smallpox." Health Library, December 30, 2011.

"Smallpox." National Institute of Allergy and Infectious Diseases, August 20, 2008.