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
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
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
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
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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