Unit 4: Infectious disease
Infectious Disease
• The #1 cause of death and disability in the
world today
• Infectious diseases are not as big of a concern
in developed countries such as Canada
– Except in people with poor immune systems
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Infants
The elderly
Malnourished people
Alcohol abusers
Infectious Disease
• Caused by infection.
• Infection = when a microorganism (ex. Bacteria, virus)
invades the body which is typically accompanied by
damage to cells
• Invasion is followed by a latent period, which is
the time between infection and the development
of symptoms/signs
Pathogens
• Pathogens are disease causing agents
• Ex’s:
– Viruses non-living organisms composed of DNA or RNA
enclosed in a protein coat.
• Require host to survive
– Bacteria single-celled organisms that can live
outside of the body
– Fungi
– Parasites (ex. Tapeworms, amoeba)
• Survive by compromising host
Antigens
• All pathogens contain antigens
• Antigen = “antibody-generating”
• It is a protein/sugar on a microorganism’s
surface that our immune system recognizes
and tries to eliminate
Natural Defence to infection
• Skin
A pathogen can enter through a
lesion (cut) in the skin
• Cilia
• Mucus
• Elevated body temperature
Natural Defence to infection:
The Immune system
• Immune system= complex system in the body that
helps protect against pathogens and disease
– Key immune components:
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Macrophages
Antibodies
B-Cells
T-Cells
Memory B-Cells
Memory T-Cells
Organs of the immune system
Macrophages
• Macrophages (“big eaters”): a cell that surrounds
and digests foreign matter
Macrophage
ingesting 2 red
blood cells
Antibodies
 Antibodies: Specific
proteins that stick to the
specific antigens of
pathogens.
 They cause pathogens to
clump so:
 they cannot enter cells
 they can be more
effectively excreted
Key immune components
• B-cells: once activated, have one of 2 fates:
– Become plasma cells which secrete antibodies
– Become memory cells to fight off the same infection in the
future
• T-cells: there are several types
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Helper T cells: help other immune cells
Cytotoxic T cells: destroy virally infected cells
Memory T cells: fight off the same infection in the future
Regulatory/suppressor T cells: make sure response isn’t
overactive
Key Immune components
 Memory T-cells/ memory B-cells: created the first
time a certain type of pathogen enters the body while
regular B-cells and T-cells are fighting infection.
 The next time the same pathogen enters the body,
they are already ready, waiting to eliminate that
pathogen.
 Therefore, the secondary response is much quicker!
[Ab] mg/ml
serum
Days
Immunity
• Immunity refers to the ability of your body to
resist infection so that signs/symptoms and
disease do not develop
• Ex. I already had chicken pox once, so now I
am immune to it (I won’t get it again)
4 Ways of Getting Immunity
 Natural Immunity (occurs naturally)
 Active Natural: get exposed to pathogen
 Passive Natural: Fetus receives antibodies from mother
 Infant receives antibodies from breast milk
 Conferred Immunity (received from an outside source)
 Active Conferred: vaccination (ex. A flu shot)
 Passive Conferred: get antibodies
 ** The Active methods are mostly permanent
 ** The Passive methods are temporary
Transmission of Infectious Disease
 Many infectious diseases are communicable,
which means that they can be passed from one
person to another in one of the following ways:
 Direct contact
 Indirect contact
 Airborne transfer
 Contaminated water
 Vector transmission
Chain of Infection
Chain of Infection example:
H1N1 Virus (swine Flu)transmission
Human #1
shakes hands
with Human #2.
Indirect Contact
Human# 1
infected
H1N1 virus
(swine Flu)
Human #1
touches
nose with
hand,
pathogen
exits NOSE
Infected
human #2
Human #2
wipes mouth
with hand.
Pathogen
enters through
MOUTH
A little more on H1N1
• A virus consisting of viral genes that are
similar to a human, a bird (avian) and 2 types
of pig viruses
• First identified in Mexico in April, 2009
• June 11, 2009 the WHO declared it a level 6
pandemic
H1N1
• Symptoms include fever, cough, sore throat,
runny nose, body aches, chills, fatigue,
diarrhea, vomiting
• People over 60 may have some immunity to it
• The effects of this recent outbreak have been
relatively minor
– What if the virus mutates further and it becomes
more aggressive??
– This coming winter season has many health
officials worried
Control of Infectious Disease:
Personal Level
 Hand washing, alcohol based sanitizers
 Cover mouth/nose when you cough/sneeze
 Avoid touching eyes, nose or mouth
 Bug spray
 Drink clean water
 Stay home if sick
Control of Infectious disease:
Community level
 Pasteurization: heat-treating fluids (ex. Milk)
 Antibiotics: kill microorganisms such as bacteria
 Vaccination: ex. Polio, flu vaccine
 Adequate housing: minimizes exposure to pathogens
 Nutrition: eating well raises your immunity
 Public sanitation
Control of Infectious Disease at
Community Level:
Antibiotics
• Antibiotics kill or inhibit the growth of bacteria
• Their discovery, specifically the discovery of penicillin
(Flemming, 1928), has dramatically decreased death
from infectious disease
• However, natural selection (survival of the fittest) has
occurred and now many bacteria that exist today are
resistant to several antibiotics
Third world infectious disease control
• Immunization (ex. giving them vaccines)
• Insecticides
• Clean drinking water
• Public Hygiene
• General economic and social development