lecture 1

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2 Nov 2010
School
Department
Course
Disease transmission
Parasites
: organism that grows, feeds, and is sheltered on or in a different
organism (host) and 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
Macroparasites
: composed of many cells; does not multiply in a host, instead it
lives certain cycles/stages through transmission stages - eggs and larvae which
passes into the external environment
Transmission
: movement from a parasite from host or host (direct or indirect)
Incubation period
: interval of time required for a 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 (ability)
Zoonotic infections
: animal infections that can be transmitted to humans
Main factors that influence the occurrence of a disease -
- Three main factors:
host
[factors: immunity, genetics, nutrition]
agent
[biological, physical, chemical, psychosocial; rate of
growth; persistence]
environment
[promotes exposure]
A person develops severe cramps after drinking from a well located on a cattle farm -
host: person, environment: contaminated water, agent: bacterium
Modes of disease transmission
- Direct - through direct contact (person to person)
- Indirect - through a common route (air, water, mosquito)
Portal of entry:
- Dermal - through the skin (fungi)
- Ingestion - through the mouth (e coli in water)
- Inhalation - during respiration (particulate matter)
Types of diseases
Iceberg concept - spectrum of disease severity
Host response
Death of organism
Classical and severe disease clinical
Moderate severity, mild illness disease
Infection without clinical illness (asymptomatic infection) subclinical
Exposure without infection disease
Tuberculosis
: infectious disease that most commonly attacks the lungs
Measles
: common skin rash, transmitted from respiration
Rabies
: affects central nervous system, transmitted through saliva
Types of disease outbreaks
Endemic
: usual occurrence of a given disease with a given geographical area
(certain area)
Epidemic
: occurrence of a disease in excess of normal expectancy in a defined
region
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