To control infectious disease
we must consider such aspects
The origin of the outbreak
(especially the natural reservoir)
Its mode of transmission within
The possible methods that can be
employed to contain it
Spread of Disease
The best method of disease control is to prevent the disease
spreading in the first place.
The four main methods by which the spread of
infectious disease is controlled are through:
environment Treatment Immunization
Modifying the Environment
All pathogens require certain conditions for growth,
reproduction, and transmission.
By modifying the environment to make it less suitable for
pathogens, most infectious diseases can be controlled.
Draining swampy ground to eliminate breeding sites for
mosquitoes carrying malaria and dengue fever.
to sterilize potentially
Workers spray drainage ditches
with insecticide to kill mosquitoes
The development of effective sanitation, sewage treatment, and
the treatment of drinking water has virtually eliminated
dangerous waterborne diseases from developed countries.
These practices disrupt the normal infection cycle of pathogens
transmitted through the fecal-oral route, such as those causing
typhoid fever and cholera.
Transmission of disease can be
prevented or significantly reduced
by adopting ‘safe’ behaviors.
Using condoms to reduce the spread
of sexually transmitted diseases.
Establishing quarantine and
isolation procedures to prevent the
spread of disease from other
Adopting appropriate personal
hygiene practices, such as washing
your hands after going to the toilet
and before handling food.
Vaccination or immunization is a
procedure that provides artificially
acquired active immunity for the
person receiving it.
A vaccine is a suspension of
microorganisms (or portions of them)
which protects people from disease by
Vaccines that are effective against
bacteria and viruses have been
produced, but to date there are no useful
vaccines for humans against protozoa,
roundworms, flatworms, or fungi.
The last known person in the world to have smallpox, 23 year
old Ali Maow Maalin (photo), from Merka, Somalia. Smallpox
was eradicated due to a vigorous vaccination program.
Types of Vaccine
There are two basic types of vaccine:
subunit vaccines and whole-agent vaccines.
Contains some part
or product of micro-
organisms that can
produce an immune
Subunit Vaccines 1
Subunit vaccines contain some product of, or fragments of,
microorganisms. These are capable of providing an
immune response in the person receiving the vaccine.
Some pathogens produce polysaccharide
capsules that are poorly antigenic,
especially in young children.
To enhance their effectiveness, they are
combined with proteins such as toxoids
from other pathogens.
Produced using genetic engineering
techniques when other microbes (bacteria
and yeast) are genetically altered to make
the desired antigenic fraction.
Subunit Vaccines 2
Toxoids are bacterial toxins that have
been inactivated by heat or chemicals.
When injected, the toxoid stimulates the
production of antitoxins.
Heat, iodine or
These are produced by fragmentation of
a conventional whole-agent vaccine and
collecting only those portions containing
the desired antigens.
Whole Agent Vaccines
Whole agent vaccines contain
complete microorganisms that are
nonvirulent (not capable of
They may be either inactivated
whole or attenuated.
Many attenuated viruses provide
recipients with life-long immunity
(without the need for booster shots).
An effectiveness of 95% is not
One danger of such vaccines is that
these live viruses can back-mutate to
a virulent form.
Inactivated: whole agent is
inactivated by treatment with
formalin or other chemicals
Attenuated: The agent is alive, but has been
significantly weakened. They are usually
derived from strains where mutations have
accumulated during long-term cell culture.
Using genetic material to produce vaccines is one
of the promising new fields of vaccine research.
Unlike traditional vaccines (which contain either whole
or parts of a pathogen), genetic vaccines contain only
the gene for producing an antigen from the pathogen.
When this gene is expressed in a patient the protein
produced elicits an immune response.
Genetic vaccines are currently being developed and
trialed to immunize people against:
Producing a DNA Vaccine 1
The recombinant bacteria
are allowed to grow and
reproduce on an agar plate.
Antigen gene is spliced
into the plasmid and the
plasmid is inserted back
into the bacterium.
Gene for the antigen
is removed from the
Plasmid is isolated from
a harmless bacterium.
Producing a DNA Vaccine 2
Expression of the gene in the
patient produces a protein that
elicits an immune response.
The isolated antigen gene is
delivered to the patient using direct
injection or via a gene gun.
Antimicrobial drugs include synthetic
(manufactured) drugs as well as drugs produced
by bacteria and fungi, called antibiotics.
Antibiotics are produced naturally
by microorganisms as a means of
inhibiting competitor microbes
around them (a form of antibiosis,
hence the name applied to the drugs).
The first antibiotic, called penicillin, was
discovered in 1928 by Alexander Fleming.
Since then, similar inhibitory reactions between colonies
growing on solid media have been commonly observed.
Antibiotics are actually rather easy to discover, but few
of them are of any medical or commercial value.
Agar plate with
and antibiotic discs
Antimicrobial Effectiveness 1
To be effective, antimicrobial drugs
must often act inside the host so
their effect on the host’s cells and
tissues is important.
The ideal antimicrobial drug has
selective toxicity, killing the harmful
organism without damaging the host.
Some antimicrobial drugs have a
narrow spectrum of activity and
affect only a limited number of
The wrong antibiotic can
allow infections such as this
ulcer to get out of control
Antimicrobial Effectiveness 2
Other drugs affect a large variety of
microbes and are therefore called
The identity of a pathogen is not
always known. Therefore a broad-
spectrum drug may be prescribed
in order to save valuable time.
However there is a disadvantage
with this practice. Broad spectrum
drugs not only target the pathogen,
but also the host’s normal microbial
Staphylcoccus aureus infection
The sticky looking substance is a polysaccharide biofilm,
which protects the bacteria from antibiotics. Some strains of
staph. have developed resistance to multiple antibiotics. The
wide use of broad-spectrum antibiotics has contributed to this.
Spectrum of antimicrobial activity of
a number of chemotherapeutic drugs
Spectrum of antimicrobial activity of
a number of chemotherapeutic drugs
How Antimicrobial Drugs
Antimicrobial drugs disrupt the functioning of a bacterial cell in the following ways:
Inhibited Protein Synthesis
Translation is disrupted.
Damaged Cell Walls
The synthesis of new cell walls
during cell division is inhibited.
Examples: penicillin, vancomycin,
Damaged Plasma Membrane
The plasma membrane may be
ruptured. Examples: nystatin,
miconazole, polymyxin B,
Inhibition of Enzyme Activity
The synthesis of essential
metabolites is inhibited.
Inhibit Gene Copying
DNA replication and transcription
are interfered with. Examples:
A monoclonal antibody is an artificially produced antibody that
neutralizes only one specific protein (antigen).
Monoclonal antibodies are produced by
stimulating the production of B-cells in
mice injected with the antigen.
These B-cells produce an antibody against
B-cells can be isolated and made to fuse with
immortal tumor cells.
They can then be cultured indefinitely in a
suitable growing medium.
Monoclonal antibodies are useful for 3 reasons:
They are totally uniform (i.e. clones).
They can be produced in large quantities.
They are highly specific.
Monoclonal antibodies chemically
linked to a fluorescent dye to
detect the presence of gonorrhea
Making Monoclonal Antibodies
Mouse cell and
tumor cell fusing
Pure tumor cells are
harvested from culture
A mouse is injected with a
foreign protein (antigen).
The mouse’s B-cells produce an
antibody to recognize the antigen.
A few days later, antibody-
producing B-cells are taken
from the mouse’s spleen.
The mouse cells and
tumor cells are mixed
together in suspension.
Some of the mouse cells fuse
with tumor cells to make hybrid
cells called hybridomas.
Hybridomas are screened for
antibody production. They are then
cultured to produce large numbers
of monoclonal antibodies.
The mixture of cells is placed in
a selective medium that allows
only hybrid cells to grow.
The World Health
Founded in 1948, the World Health Organization (WHO) is a
specialized agency of the United Nations
WHO promotes technical cooperation for health among nations,
carries out programs to control and eradicate disease, and strives to
improve the quality of human life.
WHO has four main functions:
To give worldwide guidance in the field of health
To set global standards for health
To cooperate with governments in strengthening national health programs
To develop and transfer appropriate health technology, information
A major event in WHO's first 50 years was the global eradication of smallpox.
The Role of the CDC
The Center for Disease Control and Prevention (CDC) is an
agency of the US Department of Health and Human Services.
In today's global environment, new diseases have the potential to spread
across the world in a matter of days, or even hours, making early detection
and action more important than ever.
The CDC plays a critical role in investigating, monitoring and controlling these
diseases, traveling at a moment's notice to investigate outbreaks worldwide.
CDC and Zairian scientists
take samples from
animals collected near
Kikwit, Zaire, 1995. These
samples were sent back to
CDC in Atlanta for testing
to search for the animal
reservoir of the Ebola