Smallpox: A Threatening Epidemic
Ralph Morris, MD, MPH

The author is a Public Health Preparedness Consultant to the Minnesota Department of Health, and a member of the Water Quality and Health Council. The views expressed here are his own.

Smallpox has been described as the world's greatest killer, claiming more than 500 million victims in the twentieth century alone. Although smallpox was eliminated worldwide as a natural disease in 1977, today we are faced with a renewed threat of a smallpox epidemic. The existence of unauthorized stocks of smallpox, coupled with a large, unvaccinated population in the world, opens the door for a potential public health emergency. The smallpox vaccine, while posing small risks of its own, is our best available defense against this potential threat.

What is a public health epidemic, and why is smallpox a potential a public health emergency? An epidemic is the occurrence of a disease in a greater than expected number of cases for a given place or time. In the case of smallpox, a single confirmed case in the world would represent an epidemic. A public health emergency has several characteristics, including:

• Risk of introduction and spread of a disease into a population;
• An unusually large number of cases;
• Severe disease, causing death and/or permanent disability;
• Social and/or economic disruption of a society;
• Governmental authorities cannot adequately cope with the threat; and
• Danger of international transmission.

Just as Sudden Acute Respiratory Syndrome (SARS) represents a public health emergency today, smallpox has all the characteristics to be the public health emergency that we could face tomorrow.

Smallpox is a double stranded DNA virus that is only known to infect humans. The smallpox virus causes a three-stage rash disease, which can be spread by airborne transmission, respiratory droplets, or contact with skin lesions, bedding and clothing. The first stage of the disease is the incubation period, usually lasting 12 days, in which the patient is asymptomatic. The prodromal stage last 2 to 4 days, during which time the patient has a nonspecific, flu-like illness with a high fever. During the eruptive stage, a characteristic rash appears and the patient is highly contagious to non-vaccinated contacts. The rash initially appears macular, then papular, progresses to vesicles, pustules appear and finally pustules dry to scabs. The patient is contagious until the scabs fall off. The rash is unique in that all the lesions appear at the same stage of development on the same part of the body. In addition, the lesions appear on the palms of the hands and soles of the feet. The disease is fatal in 20% to 40% of the cases and can leave disfiguring scars in the survivors. An index case will typically infect 6 to 8 contacts in the household or hospital setting.

Smallpox has killed throughout the ages, with the first known case being Ramses V in Egypt in 1157 B.C.. The downfall of the Aztec and Inca Empires were caused, in part, by smallpox imported to the New World by the Spanish. During the French and Indian War, the British used smallpox-laden blankets to weaken Indian allies of the French. In 1796 Edward Jenner found that innoculation with the cowpox virus protects humans from smallpox. Following a comprehensive public vaccination program, the last case of smallpox in the United States was in 1949. The U.S. discontinued smallpox vaccinations in 1972. Under the auspices of the World Health Organization, endemic smallpox was eliminated from the world in 1977, through aggressive case identification, containment of cases and contacts, and contact vaccination. By joint agreement, the remaining authorized smallpox virus repositories are in Atlanta, GA and Koltsovo, Russia.

Although smallpox has been eliminated as a natural disease for over 25 years, it quite possibly exists as a potential biological weapon. At least four countries, including Iraq, are believed to have unauthorized stocks of the smallpox virus. Former Soviet Union scientists have confirmed that smallpox was successfully weaponized, despite the fact that such research and development was illegal. These same scientists also confirm that the Soviets successfully tested weaponized smallpox in bombs and missiles. Active research has been undertaken to engineer more virulent strains than the naturally occurring disease. Just as with weaponized anthrax, no one can predict how weaponized smallpox would affect susceptible populations or how quickly it would spread. The existence of unauthorized stocks of smallpox coupled with a large, unvaccinated population in the world opens the door not only for a public health emergency, but a true nightmare.

The current smallpox vaccination uses a live virus called vaccinia, which is very similar to the cowpox virus that Jenner used in 1796. Although this vaccine is responsible for erasing the disease from the face of the earth, it is not without its complications. The vast majority of individuals have no problems with the smallpox vaccination. However, in a very small number of cases there can be local reactions to the vaccination site, secondary spread of the vaccination site, and certain life threatening conditions. Individuals who are pregnant, have a compromised immune systems, have certain skin conditions, or who have household contacts with these conditions should not be given preventive vaccinations. In the event of an actual smallpox attack, however, all individuals that have direct contact with smallpox cases should be vaccinated.

In addition, the U.S. Centers for Disease Control and Prevention (CDC) reported that monitoring of smallpox vaccinations has suggested that the vaccine may cause heart inflammation, inflammation of the membrane covering the heart, or a combination of these two problems. However, the CDC notes that it is not known at this time if the smallpox vaccination caused these problems or if they occurred by chance alone. As a precautionary step, the CDC recommends that individuals who have been diagnosed with a heart condition (with or without symptoms) to NOT get the smallpox vaccine at this time while researchers continue their investigations.

Currently in the United States, volunteer public health workers and hospital-based healthcare workers are receiving vaccinations as a first defense against a possible attack. As of this date, approximately 30,000 workers have been vaccinated. In the next phase of the program, additional healthcare workers and first responders are to be vaccinated. The future of the program is somewhat uncertain with the unresolved issues of liability, compensation, contraindications to the vaccine and unknown threat of the disease. Many professional associations, physician groups, hospitals, labor unions, state and local governments are reluctant to proceed with the vaccination program given these controversies.

It is ironic that the smallpox vaccine has become as controversial as it has. Faced with a threatened smallpox attack, the vaccine is the only defense we have other than isolation and quarantine. With the possible exception of providing safe water supplies, no other preventive health intervention has had as beneficial an impact on reducing morbidity and mortality from infectious disease as the smallpox vaccine.