Smallpox: eradication, storage, and potential use as a bacteriological weapon

Historically, smallpox was one of the most feared diseases in the ancient world. After an extensive and successful eradication program, the World Health Organization (WHO ) certified the global eradication of smallpox infection in 1980. There has not been a single reported case of smallpox infection in over 20 years. However, smallpox was once a deadly disease with the power to decimate populations. Successful efforts to prevent the spread of smallpox through vaccination changed the course of Western medicine and indeed, the history of smallpox is a fascinating testament to the effect of health and disease on the development of modern civilization. Today it is difficult to imagine the devastating effects of the disease on the human population. In 1981, smallpox was removed from the WHO list of diseases covered under the International Health Regulations, which detail notification requirements and measures that should be taken to contain an outbreak. The last reported case of smallpox occurred in Somalia in 1977, and on May 8, 1980, the WHO declared the global eradication of smallpox. This meant that smallpox vaccination was no longer required and the WHO indicated that only "investigators at special risk" should have the vaccine . It was also decided that seed lots of vaccinia virus would be maintained as well as stocks of 200 million doses of prepared vaccine in case of an accidental outbreak. There is a 30% case-fatality rate associated with smallpox infections among unvaccinated individuals and routine vaccinations have now not been performed in the United States in over 25 years. The fact that stocks of smallpox still exist means that an accidental or deliberate release of the virus could occur. Smallpox, if used as a biological weapon, clearly presents a threat to both civilian and military populations. Thus, although there is little risk of naturally occurring smallpox infections at this time, there is a significant potential for a smallpox epidemic of manmade origin.

The concept of using the variola (smallpox) virus in warfare is an old one. During the French and Indian Wars (1754–1767), British colonial commanders distributed blankets that were used by smallpox victims in order to initiate an epidemic among Native Americans. The mortality rate associated with these outbreaks was as high as 50% in certain tribes. More recently, in the years leading up to World War II, the Japanese military explored smallpox weaponization during operations of Unit 731 in Mongolia and China.

There are a number of characteristics that make the variola virus an excellent candidate for use as a biological weapon. An aerosol suspension of variola can spread widely and have a very low infectious dosage. In general, the dissemination of a pathogen by aerosol droplets is the preferred deployment method for biological weapons. Smallpox is highly contagious and is spread through droplet inhalation or ingestion. As there are no civilian or military smallpox vaccination requirements at this time, a large susceptible population is at risk from the infection. The incubation period in naturally occurring cases averages seven to 14 days. However, the period could be shortened to three to seven days, especially in the cases of aerosol application. People who have contracted the disease are contagious during the late stages of the incubation period, even though they remain asymptomatic. Thus, transmission of the disease can occur as early as two days after exposure to the virus. Depending on the climate, corpses of smallpox victims remain infectious for days to months. The duration of the disease is long and coupled with the complex isolation and protection requirements of smallpox treatment, each infected person would require the efforts of several medical support personnel.

In general, the worldwide practice of smallpox immunization greatly diminished the fear of an epidemic caused by a deliberate release of the virus. Although the disease was declared eradicated in 1980, stores of smallpox officially exist at the two WHO-approved repositories. The first is at the Centers for Disease Control and Prevention in Atlanta, USA. The second is the State Research Center for Virology and Biotechnology (also known as Vector) at Koltsovo, in the Novosibirsk region of Siberian Russia. In June 1995, WHO inspected the Koltsovo facility and determined that it was an acceptable storage facility after the virus stocks were moved there from the original storage site at the Institute of Viral Preparations in Moscow. All other laboratories around the world were required to destroy their remaining stores of smallpox virus. Concomitantly, WHO recommended that all countries discontinue vaccination against the disease.

Despite the provisions of the WHO and the 1972 Biological Weapons Convention , the former Soviet Union maintained a sophisticated and large-scale research and development program for biological weapons implementation. This research was carried out at both military and civilian level. It is now known that the Soviet Union successfully developed and adapted smallpox virus for use in strategic weapons.

Considerable debate has ensued regarding the officially remaining stores of smallpox virus. The WHO Ad hoc Committee on Orthopoxvirus Infections has, since 1986, consistently recommended destruction of the remaining reserves of the smallpox virus. The initial proposal was to destroy the remaining stocks in December 1990. However, the possibility that smallpox has been, and might be, incorporated into biological weapons has encouraged the scientific community to continue research on the pathogen. Although the tentative date set for the destruction of all remaining smallpox stores is late 2002, a consensus among scientists and military strategists has not yet been reached and in view of current political unrest in areas such as the Middle East, total destruction of all stores is not likely to happen.

Since many laboratories involved in biological weapons research and development in the former Soviet Union are now working with decreased funding, staff, and support, there is concern that bioweapons resources and expertise may spread to other countries. A report from the Washington Center for Strategic and International Studies states that at least 10 countries are involved in biological weapon research programs. The ability of a group to acquire variola and develop it as a biological weapon is limited by several factors. Specialized skills are required to grow smallpox in effectively large quantities and to adapt it for use as an aerosol-based weapon. It is unlikely that small, technically limited facilities or dissident groups would use smallpox as a weapon. Also, the open use of a biological weapon by any nation or political state would undoubtedly elicit severe retaliation. Lastly, the smallpox virus is not as readily available as other agents of biological terrorism, such as anthrax (Bacillus anthraci ) or plague (Yersinia pestis). Therefore, analysis of these and other factors have led bioweapons experts to conclude that well-financed and highly organized private groups or politically/state financed terrorist groups would be the most likely to use smallpox as a bio-weapon.

See also Bioterrorism; Bioterrorism, protective measures; Epidemics, viral; Viruses and responses to viral infection