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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
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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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