Transcript Powerpoint for Lecture, 24 Nov. - Nipissing University Word

Modern Science
vs.
Infectious Disease
Modern Medicine
• Although modern medicine has its roots in the early modern period,
it was not really until the last third of the 19th century that an
understanding of infectious disease could be grounded in empirical
proof
• From that time to the second half of the 20th century there was a
growing optimism that modern medical science could eradicate
infectious disease with vaccines and later antibiotics
• Since the 1970s, however, that confidence has been shattered with
the spread of new pathogens, and mutations that are resistant to
vaccines and antibiotics
Smallpox inoculation
• The practice of inoculation for smallpox is ancient, practiced in India
and China
• The simple idea behind it is to expose a person with no immunity to
smallpox to material from a smallpox pustule directly into the skin;
this produces a less severe infection than naturally acquired smallpox,
but still offers the immunity to it
• The practice was introduced into Europe in the eighteenth century by
Lady Mary Wortley Montagu, who had learned about the procedure
in Istanbul while accompanying her husband as British Ambassador to
the Ottoman Empire in 1718
Lady Mary Wortley Montagu
• In 1721, having returned to England, a smallpox epidemic
was breaking out and she asked her physician to
inoculate her children
• Because she was one of society’s elites, she was able to
interest many other aristocrats in the practice of
inoculation, including the royal family
• Because of this elite support, the practice became widely
known and practiced, both in Britain and in the colonies
• This process was known as the arm-to-arm process,
because a live infected person was needed in order to
administer the inoculation
The development of cowpox vaccine
• There were dangers, however, in inoculation; some
people could die from being exposed to the disease
• One English country doctor, Edward Jenner, noticed in
1796 that people who had suffered from cowpox were
also immune to smallpox
• Cowpox was a disease that affected the udders of cows,
and was commonly transferred to the hands of
milkmaids
• Jenner transferred the matter from a cowpox lesion
under a young boys skin, who contracted a mild form of
the disease; a couple of months later he inoculated the
child, who did not get ill from the smallpox virus
Cowpox
lesions on a
dairymaid’s
hands
• Edward Jenner
performing a
vaccination using
cowpox in 1796
• Jenner published his findings in 1798
• He coined the term ‘vaccination’ which
he borrowed from the Latin word for
cow – vacca
• Within one or two years, doctors from
across Europe and America were
following the procedure
Not everybody immediately agreed with vaccination; this satirical drawing by James Gilray
in 1802 illustrates the popular conception that cowpox vaccination could give people cowlike features
Germ theory of disease
• Even with the growing use of vaccination, there was still a major
dispute in the medical science community about the cause of the
spread and transmission of infectious disease in the nineteenth
century
• In many scientific circles the Miasma theory – where diseases were
spread through contaminated air -- continued to dominate and the
idea that microscopic germs were the cause were considered too
crazy to be true
• Several scientists in the nineteenth century proposed germs theories
of infectious diseases, but could not gain the same currency
Louis Pasteur (1822-1895)
• One of the breakthrough scientists in
the field was the French microbiologist
Louis Pasteur
• His experiments with bacteria led to
breakthroughs in the application of
germ theory to clinical medicine
• He showed in his experiments that
microorganisms were responsible for
spoiling beverages, and developed the
method of heating beverages to
remove bacteria (pasteurization)
Robert Koch (1843-1910)
• A German physician and researcher whose
main contribution was to use the microscope
as a tool to see microorganisms – thus allowing
him to isolate and grow them – and to show
that a specific microorganism is the specific
cause of a disease
• His research led him to find the causative
microorganisms for anthrax, cholera, and
tuberculosis
Koch’s postulates
• 1.
• 2.
• 3.
• 4.
The organism must always be present, in every case of the
disease.
The organism must be isolated from a host containing the
disease and grown in pure culture.
Samples of the organism taken from pure culture must cause the
same disease when inoculated into a healthy, susceptible animal
in the laboratory.
The organism must be isolated from the inoculated animal and
must be identified as the same original organism first isolated
from the originally diseased host.
Golden age of microbiology (1860-1910)
• Building on the advances made by Pasteur and Koch, a new
generation of bacteriologists set to work on finding the causative
agents for all of the known infectious diseases
• By the end of this period there was almost unanimous agreement
among scientists about the germ theory of disease, and several other
theories like Miasma (bad air) and ”spontaneous contamination”
were rejected almost overnight, putting the study of disease, and of
disease prevention on a new footing
• Building on the rapid advances in microbiology opened the door for
other types of research to combat infectious diseases
The development of antibiotics
• The German physician and scientist Paul Ehrlich
(1854-1915) was one of the first people to
conceive of creating a drug that could combat a
particular microorganism without harming other
cells – which he called a ”magic bullet”
• This put other scientists on the quest to discover
or produce chemicals that inhibit the growth of
bacteria in order to treat bacterial infections
• Ehrlich coined the term ‘chemotherapy’ – the use
of chemicals to treat a disease and discovers an
important antibiotic -- Salvarsan
Alexander Fleming (1881-1955)
• In 1928 Fleming, a Scot, discovered the
antibiotic substance benzypenicillin (Penicillin G)
from mould – marking the beginning of modern
antibiotics
• The discovery of penicillin – a broad spectrum
antibiotic (i.e. it can neutralize several bacteria)
– was one step ... Over the next decade or so the
challenge was to be able to mass produce it
• Fleming was cautious about the use of penicillin,
especially in the correct dosage
Wars in the
th
20
Century
• The world wars of the 20th century, and other conflicts gave ample
opportunity for medical research and a pressing need for the
development of cures to deal with infectious diseases that are
associated with warfare
• World War II especially gave new impetus for the discovery of
antibiotics to deal with the thousands of wounded soldiers and
civilians
• As we have seen, historically warfare and infectious disease went
hand in hand; WWII was the first war where combatant nations had
the ability to prevent mass epidemics among soldiers and civilians
Antimicrobial resistance
• Despite the great discoveries of new antibiotics in the post-WWII
period, or perhaps because of it, it was found that some microbes
developed resistance to antibiotics – so-called superbugs
• Antimicrobial resistance grows over time (as the microbes evolve)
through genetic change; thus the drugs that were so effective in the
1950s are no longer as effective
• One of the main reasons for the rise in antimicrobial resistance is the
overuse or misuse of antibiotics (i.e. they do not work on viruses)
• Scientists are predicting that we are currently in the midst of an
emerging crisis as a result of of the growth of antimicrobial resistance
New pathogens
• Just as older pathogens are changing and modifying to resist human
efforts to kill them, so new pathogens are making their way into the
human world
• HIV-AIDS, SARS and Ebola are examples of pathogens that have
recently made the leap from animals to humans, and have a deadly
force to them
• This makes some critics question whether we have not become too
comfortable with the idea that science can stay ahead of microbes,
especially since microbes have the upper hand in the relationship
between pathogen and host
A look ahead
• On Tuesday we will discuss the final exam. I will provide you with
some sample questions and offer you some ideas and strategies for
studying for the exam
• On Thursday I shall offer some final thoughts to tie the course
material together and there will be time for questions about the final
exam