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Chapter 1

PLAGUES AND PEOPLE LEC 1 - CHAPTER 1 and 2 - Introduction to disease ecology.docx

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Health Studies
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Caroline Barakat

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PLAGUES AND PEOPLE Lecture 2 – Introduction to Disease Ecology Parasites – organism that grows, feeds, and is sheltered on/in a different organism and that does not contribute to the survival of its host Virus – ultimate micro-parasite-smaller than bacteria; neither cells not 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 ex: plasmodium Transmission – movement of a parasite from host to host Incubation Period -interval of time required for development of a disease -cannot see symptoms -see a period of activity (doing something inside the host) Latent Period -seemingly inactive period between exposure to an infection and subsequent illness - cannot see anything inside the host -disease is sleeping (dormant) Parasite virulence -capacity of a parasite to cause disease -high virulence = greater harm Zoonotic infections -animal infections that can be transmitted to humans What are the main factors that influence the occurrence of a disease? Epidermal triad8 1. Host: immunity, genetics, nutrition ex: person 2. Environment: promote exposure ex: contaminated water, air, food, etc 3. Agent: biological, physical, chemical, psychosocial (ex: stress), rate of growth, persistence ex: bacterium Modes of Disease Transmission Direct transmission: from person to person Indirect: through a common route/vector (ex: needle) ex: contaminated water/air, mosquito Portal of Entry: Dermal – through the skin ex: fungus Ingestion – through the mouth ex: E.coli in water Inhalation – during respiration ex: particulate matter Aspiration – airway entry Types of Diseases: broad spectrum of disease severity – Iceberg concept HOST RESPONSE Clinical disease : Classical and severe disease Moderate severity mild illness Subclinical disease : infection without clinical illness (asymptomatic infection) Exposure without infection Tuberculosis – infectious disease that most commonly attacks the lungs CLASS A: INAPPARENT INFECTION FREQUENT Measles – common skin rash, transmitted from respiration CLASS B: CLINICAL DISEASE FREQUENT; FEW DEATHS Rabies – affects central nervous system; transmitted through saliva CLAS
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