HLTB21H3 Lecture Notes - Pneumonic Plague, Plague Of Justinian, Septicemic Plague

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24 Apr 2012
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HLTA01H3F- The Power of Plagues
Lecture 2
Definitions
Parasites: organism that grows, feeds, and is sheltered on or in a different organism and that
does not contribute to the survival of its host
Virus: ultimate micro-parasite- smaller than bacteria; neither cells nor organisms; can only
reproduce within their host
Macro-parasites: composed of many cells; cycles through transmission stages (eggs and larvae)
which pass into the external environment
Transmission: movement of a parasite from one host to another
Incubation period: interval of time required for development of a disease
Latent period: seemingly inactive period between exposure to an infection and subsequent
illness
Parasite virulence: capacity of a parasite to cause disease
Zoonotic infections: animal infections that can be transmitted to humans
What are the main factors that influence the occurrence of a disease?
1. Host
Immunity
Genetics
Nutrition
2. Environment
Promotes exposure
3. Agent
Biological, physical, chemical, psychosocial, rate of growth, persistence
Modes of Disease Transmission
Direct transmission: from person to person
Indirect: through a common route/vector, e.g. contaminated air/water, mosquito
Dermal: through the skin, e.g. fungus
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Ingestion: through the mouth, e.g. E. coli in water
Inhalation: during respiration e.g. particulate matter
Aspiration: airway entry
Types of Diseases
Broad spectrum if disease severity- Iceberg concept
Clinical Disease
o Classical and severe disease
o Moderate severity; mild illness
Subclinical Disease
o Infection without clinical illness (asymptomatic infection)
o Exposure without infection
Types of Disease Outbreaks
Three main types:
Endemic: usual occurrence of a disease within a given geographical a
rea
Epidemic occurrence of a disease
Determinants of disease outbreaks:
Herd immunity: resistance of a group to a disease attack due to immunity
o For measles- estimate that 94% of the population must be immune
Incubation period
Attack rate: ratio of the number of people in whom a certain illness develops/total
number of people at risk
Definition of Plagues
In the past, all disease outbreaks- plagues.
‘plaga’ i.e. ‘to strike a blow that wounds’
Epidemic (Geek origin)
‘epi’ “among” and ‘demos’
Historical Perspective
Belief that our ancestors ‘hunter-gatherers’ were healthy
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Agricultural Revolution
Domesticated animals
Lived in one area and were exposed to many more parasites
People lived in close proximity to each other
Spread of diseases easily
Irrigation became popular
Zoonotic diseases started to affect humans
Technological advancements
Can speed disease control
Can also speed transimission
Efficiency in transportation makes it easy to spread diseases from one part of the world
to another in a short amount of time
e.g. confined areas of an aircraft
Legionnaires Disease- 1976
The suspected source of the disease is through wet cooling/air conditioning systems
Toxic Shock Symptoms (traced to 1979)
Caused from a bacteria found in high absorbancy tampons
When these tampons were moved from the market, the outbreak of TSS drastically
declined
SARS- traced to Feb 2003
Was spread from China to Canada when a person travelled
Lecture 3
The Antonine Plague
soldiers coming from Mesopotamia back to Rome brought the disease to the Roman
Empire
According to the symptoms, it could have been the first record of smallpox
Caused more than 2000 deaths in Rome per day
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