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Tell me more about smallpox


Smallpox, the disease

Dr. Thomas is the Head of the Program in Epidemiology at the Fred Hutchinson Cancer Research Center. He previously conducted studies of smallpox and other infectious diseases. His current interests are in cancer epidemiology.

Smallpox was a disease that was caused by a virus. The virus spread when an uninfected person came in direct contact with a sick person and breathed in the virus. Usually, the virus was in tiny drops that were coughed up by the sick person. After about two weeks (the incubation period of the smallpox virus), the infected person would develop a high fever and muscle aches and pains. After about three days of fever the person would break out in a rash all over his or her body. At first it looked like red spots, but these spots gradually became blisters that were about the size of a pencil eraser. After about 5 days of rash, the fluid in the clear blisters turned to pus. The more pus spots (pustules) that a person had, the more likely he or she was to die.

There were two main types of smallpox virus: variola major, which killed about 20 percent of the people who were infected; and variola minor, which killed about 2 percent of its victims. If a person did not die, the pus gradually dried up to form scabs that dropped off after 1 or 2 weeks. The pustules on the face often left permanent scars known as pockmarks.

Smallpox was known to the ancient peoples of China, India, and Egypt. Pharaoh Ramses V died of it in 1157 BC. It spread wherever large numbers of people moved, and it was a particularly serious problem in cities where people lived close together. It first reached Europe in the fifth century, and it was one of the leading causes of death in the 16th and 17th centuries. It was brought to the Americas many times during that period, first by the Spanish conquerors and later by African slaves, where it wiped out many native American populations.

The Hindu god Krishna is believed to have loved milkmaids because of their beautiful (unscarred) complexions. Milkmaids, of course, spent a lot of time around cows, which are carriers of cowpox, a virus similar to the smallpox virus. In 1796 the British physician, Edward Jenner, after noting that milkmaids were spared the smallpox, demonstrated that if he infected the skin of someone with the scab of a cowpox sore, that person would not get smallpox. This was the beginning of vaccination. During the next 130 years, the practice of vaccination (using a virus similar to cowpox) was gradually adopted by health workers in all parts of the world, but the disease still persisted in many places where not enough people were vaccinated.

In 1965, the World Health Organization (WHO) began a world-wide effort to eradicate smallpox. Studies by epidemiologists showed that the disease could be stopped from spreading if the people who came in contact with infected persons were all vaccinated. The WHO eradication strategy was not to try to vaccinate everyone in the world, but rather to find all of the cases as soon as they developed their rashes, and then to vaccinate all the people living in the areas where the cases lived. This plan worked dramatically, and the disease was completely eradicated from the earth by 1977.

Today, the smallpox virus exists only in two freezers in Moscow, Russia, and Atlanta, Georgia, in the United States. If the virus got out, it could infect people, because people are no longer being vaccinated. However, the viruses are very carefully guarded. Scientists are currently debating whether these frozen viruses should be destroyed, or kept for possible medical research purposes.

David B. Thomas
Program in Epidemiology
The Fred Hutchinson Cancer Research Center
Seattle, WA, USA


My experience with smallpox in the early '70s.

From July 1971 through June 1978, Dr. Selassie was a Public Health Officer for the World Health Organization, and led a mobile team involved in the Smallpox Eradication Program in Ethiopia and Somalia.

For the mobile surveillance team in southeast Ethiopia and northern Somalia, the day's work began at 6:00 a.m. since it gets very warm after midday. Most people came to the mobile clinic with fully blown smallpox rashes. The rashes were typical, with characteristic accumulation of pus surrounded by an inflamed skin layer, technically known as pustules. Some patients came with no rashes but with high fever, reddened eyes, coated tongue, and badly dehydrated. Although these symptoms are common with most of the febrile disorders in the tropics, those who came to our clinic had contact with smallpox cases in their villages. Given the prevalence of smallpox at the time in the region, one could be certain that the case is smallpox and rashes were imminent. Small proportions of patients came with a milder form of smallpox where there were sparsely scattered rashes on the face and arms. These were often patients who had deliberately inoculated themselves with materials from the lesions of fully blown cases to acquire immunity to the naturally occurring disease. This practice, known as variolation, is the oldest preventive practice to allay the severity of smallpox. The biggest problem of this practice, however, was that it increased transmission of the virus. Our main mission was to discourage this practice to contain the epidemic.

Our team was primarily responsible to immunize individuals at risk of developing smallpox. However, to the villagers, this task was secondary. They expected us to cure the sick. Sometimes, villagers fetched old cases who lost their vision due to smallpox and expected us to restore their sight. We had to be careful not to disappoint our target population in order to get their compliance and participate in the immunization program. Therefore, it was incumbent upon us to blend the immunization activity with patient care and referral to the nearest hospital for anyone who needed further treatment.

The major challenge of the smallpox eradication campaign in the regions I worked was keeping the vaccines viable. High temperature makes the vaccine impotent. From the time the vaccine is produced till inoculated in a human subject, it must be kept at an optimal temperature of 5-10 degrees C. This is technically defined as the 'cold chain'. The ambient temperature in the region is 35-40 degrees C. There was no electricity in the region and we had to depend on portable refrigerators that ran on kerosene oil. Even with all the meticulous care we could implement to keep the vaccines viable, the rate of vaccine spoilage was a major problem.

Once the vaccine was administered, we had to return after 72 hrs to assess the reaction to the vaccine on a representative sample of individuals who had the vaccine. This process, known as "take rate" analysis, was the only method available to us to assess the potency of the vaccine. A potent vaccine resulted in a small swelling under the skin with redness and blister formation at the site of inoculation. The absence of any skin reaction was an indication of poor vaccine potency. However, this could also happen if individuals had malnutrition or other underlying diseases that compromised their immune status.

On an average, we immunized 300 individuals per team. We had three teams in our surveillance unit. Our target communities were isolated villages that are 100 miles apart. When areas become inaccessible due to bad weather, we used a helicopter from the regional office. We rarely resorted to the helicopters since villagers thought of them as evil machines that intrude into the humans' natural habitat. A successful campaign in these villages required the prior consultation and approval of the village chiefs. The chiefs were most of the time compliant as long as we delivered patient care with the immunization campaign.

Dr. Anbesaw Selassie
Assistant Professor in Biostatistics and Epidemiology
Preventive Medicine Program
University of South Carolina
School of Medicine


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An Access Excellence Science Mystery sponsored by Genentech, Inc.
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