HLTB21H3 Lecture Notes - Homo Erectus, Herd Immunity, Rodent
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Lecture 2 – Introduction to Plagues
Parasites
Grow, live, feed on a host but does not contribute to host survival
Cannot survive or replicate on their own (live on a host inside the body)
More offspring the greater infection can spread
Microparasite(virus): a collection of genetic material encased in a protein shell, and can only be
seen with an electron microscope (virus is smaller than bacteria) and can only reproduce within
their hosts
Macroparasite: composed of many cells; cycles through a transmission stage (eggs and larvae)
which pass into the external environment (can be seen using naked eye) ex. Fleas and ticks
Transmission, the movement of the parasite from one host to another
Incubation period – interval required for development of a disease (activity occurring but don’t
see symptoms yet)
Latent period – seemingly inactive period between exposure to an infection and illness (no
activity occur, dormant stage)
Parasite virulence the capacity of a parasite to cause disease (how much harm it can cause to a
host)
Zoonotic infections are animal infections that can be transmitted to humans
Host:
Immunity/susceptibility
Genetics
Nutrition
Environment
Living in an environment that promotes exposure (contaminated water)
Agent
Biological, physical, chemical, psychosocial, rate of growth, persistence (all three
factors have to be present in order for disease to occur)
Direct transmission – from person to person
Indirect transmission – through a common route/vector
Portals of entry
Dermal – through the skin
Ingestion – through the mouth
Inhalation – during respiration
Aspiration – airway entry
Asymptomatic infection – infection without clinical illness
Transmission can occur without anything stopping it (don’t show symptoms)