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Infectious Diseases
Nature of infectious diseases
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Pathogens
Infection
Disease
In order to cause disease, pathogens must be able
to enter, adhere, invade, colonize, and inflict
damage
Growth of pathogens or the production of
toxins/enzymes cause disease
Microbes that cause infectious diseases
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Bacteria
Viruses
Fungi
Protozoa
Helminths
Prions
Picture of Health??
Occurrence of infectious diseases
 Epidemiology –study of the occurrence of disease in
populations
 Disease reservoirs-where the infectious agent
survives (humans, rodents) Example = yersinia
pestis (plague)
 Modes of transmission
ingestion, inhalation, casual contact, intimate
contact, bites/animals
History
Emerging infectious diseases Have not occurred in humans before,
 Have occurred previously but affected only small
numbers,
 Or have occurred throughout human history, but
only recently recognized as disease due to
infectious agent
Re-emerging infectious diseases
 Once were major health problems globally or in
a particular country, then declined dramatically,
but are again becoming health problems for a
significant proportion of the population.
Prevention
 Safewater
Purification methods
 Testing against contamination
 Sewage Treatment
 Waste water plants separate components of sewage and
treat them
 Chlorination
 Food Safety
 Inspections
 Pasteurization
 Regulations
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Prevention
 Animal Control
Domestic inspections
 Vaccinations
 Sanitation
 Vaccinations
 Pre-school
 Threshold proportion
 Herd immunity
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Public Health Organizations
 NIH – supports health-related research
 CDC – investigates disease outbreaks, informs the
public
 FDA – monitors safety of foods and medicines
 WHO – coordinates health/vaccine programs
internationally
Treatment
 Bacteria (prokaryotes)
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Antibiotics “destroyer of life”
Inhibit cell wall, protein, lipid, or RNA synthesis
Penicillin was the first – interfers with cell wall
Chloramphenicol, tetracycline – protein synthesis
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Rifampicin – prevents RNA from being made
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Treatment
 Viruses
 Non-living; uses cell materials to replicate
 Highly toxic to host cells
 Target virus-specific enzymes involved in making DNA/RNA
 Acyclovir – herpes
 Amantadine – influenza
 AZT - AIDS
Treatment
 Fungi, protozoans, helminths
 Highly toxic because also eukaryotes
 Target reproduction, cell membrane, or other necessary
functions
 Choroquinine - malaria
Resistance
 Resistance
the ability of the pathogen to survive treatment by a particular
drug
 Growing problem
 Mechanism
 change in genes that allows them to evade the action of the drug
 Stuctural changes in proteins, receptors
 Transfer of anti-microbial genes
 Don’t mutate but acquire it from others
 Transformation – taking up free-floating DNA plasmids
 Transduction – virus carries resistant gene to other bacteria
 Transposons – small “rogue” sections of DNA
 Mutations and genetic exchange is rare; but bacterial growth is
high
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The body’s defense mechanisms
First Line of Defense
 Skin
 Secretions
 Non-specific defenses macrophages
 Normal Flora
The body’s defense mechanisms
Immune System
http://highered.mheducation.com/
sites/0072507470/student_view0
/chapter22/animation__the_im
mune_response.html
 Humoral (antibody) response –
B-cells
B-cell, plasma cell, antibodies,
memory B-cells
 Cell-mediated response – T-cells
helper T-cells, killer T-cells,
memory T-cells
 Vaccination produces immunity
An inside look at the flu
Need for Vaccines
 Spanish flu killed millions during WWI
 Still kills today but generally in the 100s
 Endemic – local, normal, baseline disease
 Epidemic – widespread and in large numbers at
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same time
Pandemic – world-wide
Protects individual
Lowering occurrence in population can protect those
who can’t get vaccine (herd immunity)
Threshold response - percent of people who need to
be vaccinated for herd immunity to work
Types of vaccinations
 Live but weakened disease agents
 Good but higher mutations, can cause illness, refrigeration
 Inactivated or killed disease agents
 Less effective but safer, need boosters
 Subunit vaccines – use only subunits of antigens
 Toxoid vaccines - against toxins made by bacteria
 Conjugate vaccines – helps infants recognize antigens
 DNA vaccines
 Recombinant vector vaccines
Vaccine Production
 Tested in cells and in animals
 Eggs – virus injected into fertilized eggs to reproduce
and then protein coats isolated and tested; takes up
t0 6 months
 Cell Culture – grown in confined cells; cells die and
viral coats are isolated and tested, quicker
 Pharming - tobacco plant infected with
Agrobacterium that has gene for viral coat antigen
inserted; virus-like particles of protein then isolated;
no DNA so more safety.
Issues with Vaccines
 Public perception
 Myths (autism)
 Makes me sick or allergies
 Government intrusion
 Religious freedom
 Challenges
 Speed of production
 Safety and stability
 Storage and distribution
 Changing pathogen landscape
Bioterrorism
Violent acts or acts dangerous to human life
that…appear to be intended:
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To intimidate or coerce a civilian population;
To influence the policy of a government by intimidation or
coercion; or
To affect the conduct of a government by assassination or
kidnapping.
Bioterrorism
 Biological weapons used in bioterrorism are living
microorganisms such as bacteria, viruses, fungi,
that can kill or incapacitate.
 Health care facilities may be the initial site of
recognition and response to bioterrorism activity.
Because of this, the names and telephone numbers
for internal and external departments or agencies
that need to be contacted should be kept by each
facility in its bioterrorism readiness plan.
Bioterrorism
 Response to bioterrorism agents:
 Internal reporting requirements (within a facility):
 Infection control personnel
 Epidemiologist (local and state)
 Administration (health care facility and health department)
 Office of public affairs in the health facility
Bioterrorism
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External contacts (outside of facility)
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Local health department
State Health Department
FBI
CDC
Local police
EMS
Bioterrorism
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Agents
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Bacterial- Anthrax and Plague
Viral- Small Pox
Toxins- Botulism and Ricin