Unit 4: Infectious disease
Infectious Disease
• Infectious diseases remain a leading cause of
death in low-income countries
• Not as big of a concern in developed countries
such as Canada
– Except in people with poor immune systems
•
•
•
•
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
• Antigens are how our body knows that a
specific pathogen has entered our body
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:
•
•
•
•
•
•
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
–
–
–
–
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
Infectious Diseases
Classifications of Disease Outbreak
• Endemic: restricted or peculiar to a locality or region
– Malaria is endemic to Africa
• Epidemic : affecting or tending to affect an atypically large
number of individuals within a population, community, or
region at the same time; excessively prevalent
– AIDS is epidemic
• Pandemic : occurring over a wide geographic area and
affecting an exceptionally high proportion of the population
– H1N1 is likely to be pandemic throughout the world this coming flu
season
– http://medlineplus.gov/
Bacterial Infectious Diseases
• Cholera- caused by vibrio cholerae bacterium
– Diarrhoeal infection, can result in death
– Fecal-oral transmission
– 6 significant and fatal outbreaks throughout recent history
still endemic in many countries
• Leprosy- caused by mycobacterium leprae bacterium
– Direct, indirect transmission
– 213000 current cases, mainly in Asia, Africa
– Untreated can cause skin, nerve, limb, eye damage
– curable
Bacterial Infectious Diseases
• Meningococcal meningitis- caused by several
different types of bacteria
• Results in severe infection of the meninges- thin
linings that surround the brain and spinal cord
• Can cause severe brain damage and kills 50% of
untreated cases
• Typically indirect transmission
• Symptoms include stiff neck, high fever, light
sensitivity, confusions, headaches and vomiting
Curing bacterial infections
• Bacterial infectious diseases can be cured by:
____________________________________
Viral Infectious Diseases
• Common Cold- Typically caused by rhinovirus or
coronavirus
• Symptoms include sore throat, runny nose and fever
• Influenza- caused by various strains of influenza virus
• Symptoms include high fever, dry cough, headache, sore
throat, muscle pain, runny nose
• Both: Most common transmission is through indirect
contact i.e.. Shaking hands then touching eyes, nose,
mouth
• No cure for either, immune system=defence
Do you have the cold or the flu?
H1N1 (‘Swine Flu’)
• A subtype of the influenza virus which has
genes from 2 pig, a human and a bird virus
• 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 the recent outbreaks have been
relatively minor
– BUT! What if the virus mutates further and it
becomes more aggressive??
Parasitic Infectious Diseases
• Malaria- caused by plasmodium parasites
• Vector transmission by mosquitoes
• Nearly 1 million deaths in 2008 (mostly
African children)
• Acute symptoms similar to flu, can lead to
anaemia, respiratory problems
• Antimalarial drugs exist, but are becoming
resistant
Sexually Transmitted Infectious
Diseases
•
•
•
•
•
•
•
AIDS
Genital Herpes
Hepatitis B
Gonorrhoea
Chlamydia
Syphilis
***to be discussed during the STD unit
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
Control of Infectious Disease at
Community Level: Vaccination
• Live, weakened, inactive or killed forms of the
pathogen are administered to the patient
• This administration is too low to cause
symptoms, but sufficient to stimulate the
production of antibodies
• When later exposed to the pathogen in its
natural form, your body is already prepared to
fight it with antibodies, and it is eliminated
before signs/symptoms can occur
Successful Cases of Vaccine Usage
Polio
• Caused by poliovirus
• Fecal-oral transmission
• Majority of cases show no symptoms,
paralysis in some
• Vaccine developed by Jonas Salk (1952)
• Mostly eradicated- 1982-350,000 cases,
2006– 1997 cases
• Still endemic in Nigeria, India, Pakistan and
Afghanistan
Successful Cases of Vaccine Usage:
Smallpox
• Caused by variola virus
• Killed 30% of infected, left others with scars,
blindness
• Edward Jenner inoculated people with cowpox,
found it protected from smallpox
• Effective vaccine developed and began worldwide
administration in 1950s
• 1950s-50 million smallpox cases; last case of
smallpox-1978
• WHO certified it as completely eradicated
in 1979; only disease ever with such success
Third world infectious disease control
• Immunization (ex. giving them vaccines)
• Insecticides
• Clean drinking water
• Public Hygiene
• General economic and social development