What is Yellow Fever?
Yellow Fever can be traced as far back as 400 years in historical
documents. The first outbreak happened in America in 1648. A virus
causes Yellow Fever. This usually brings on a mild reaction but sometimes
can cause death. A South African doctor called Max Theiler discovered
a vaccine 60 years ago, but people continue to die from the disease.
The Yellow Fever virus takes 3 to 6 days to develop inside a person’s
body. Sometimes there are no symptoms at this stage, but sometimes
people have a fever, their muscles hurt, they get headaches and shivers,
they lose their appetite and they feel nauseous and throw up. It can
cause the heart to slow down but usually after 3 or 4 days most of
these symptoms go away. 1 to 2 people out of 10 patients enter a “toxic
phase”. They get jaundice, stomach ache and vomit followed by
bleeding from their mouth, nose, ears, eyes and stomach. Most people
who get to this stage die in 10 to 14 days.
Yellow fever is present in tropical areas in Africa and South America,
specifically in Bolivia, Brazil, Colombia, Ecuador and Peru. In Africa
33 countries close to the equator are affected. Mosquitoes carry the
disease and humans and monkeys can get it from being bitten.
Map A: Countries at risk for Yellow
Fever and having reported at least one outbreak, 1985 – 1997.
Source: http://www.vaccinesafety.edu/yellowfever.gif
The
best way to prevent Yellow Fever is vaccination. The vaccine is very
effective and can protect a person for any period from
10 years
to life. It should be given to children at the same time as their
vaccination for measles. To prevent the spread of Yellow Fever
80% of a country’s
population has to be vaccinated.
The Vaccine
Max Theiler, a South African doctor, developed the vaccine for
Yellow Fever. In 1928 scientists discovered that the rhesus monkey
could get
Yellow Fever. This meant that these monkeys could be used in experiments
to find a vaccine. Theiler later discovered that mice could be used
in laboratories for vaccine experiments, and they were much cheaper
than rhesus monkeys so the experiments became less costly.
When developing the vaccine for humans Theiler used the virus he
had been using in mice. He injected the first group of people taking
part
in his tests with the virus on its own. The second group was injected
with the virus and human immune serum.
Both techniques were successful, but the second one carried less
risk of causing reactions in the human nervous system. It could not
be used
on large scale because a large amount of human immune serum would
be necessary and it would be too expensive. Theiler realised that
he would
have to find a replacement for the serum. Monkey, horse, rabbit and
goat immune sera were used in experiments, and although all of these
could possibly work the monkey immune serum was the most effective.
People had mild reactions to the virus and serum, but they produced
enough antibodies to protect themselves. Theiler also needed to use
less monkey serum than human serum to get the same effect.
The process was still not suitable to vaccinate large groups of people
and Yellow Fever epidemics were occurring regularly. The virus used
for vaccination or inoculation had to be grown on organic tissue.
Theiler and his team discovered that it could be necessary to use
tissue that
contained a lot of nerve tissue, like the brain. To find out how
much nerve tissue was necessary they embarked on a new experiment.
Here
they used three different tissues that all contained chicken embryos.
The first was made of whole, ground up chicken embryo, the second
contained only chicken embryo brain and the third included small
amounts of nerve
tissue from the minced chick embryo that had had its brain and spinal
cord removed before being minced. The experiment was successful
with tissue from whole chick embryos and chick embryos without brains
and
spinal chords, with the first one being the most efficient. It was
called 17D and was injected into people along with human immune serum
and has since been used to vaccinate millions of people.
Max Theiler and his team had developed a safe and standardised vaccination
for Yellow Fever and he won the Nobel Prize for Physiology or Medicine
in 1951.
Outcomes:
The learner is able to use information from sources to answer questions
about Yellow Fever and the development of a vaccine, and to communicate
knowledge and understanding of the topic through discussion and by
writing a paragraph.
Activity
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