Lecture 1 Plagues

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Published on 8 Jul 2011
-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; not able to survive on its own and it
requires a being for its survival (bottom of pg.8, 9)
-virus: ultimate micro-parasite; smaller than bacteria; neither cells not organisms; can only
reproduce within their host; genetic material wrapped in protein that can cause harm to a
-macro-parasites: composed of many cells; cycles through transmission stages (eggs &
larvae) which pass into the external environment; e.g round worms, tape worms, flies; some
live on surfaces (ticks) and some live inside body (HIV virus); some have complex life cycles
and have several hosts (malaria)
-transmission- movement of a parasite from host to host; usually caused by contaminated
-incubation period: interval of time required for a disease to develop; the time period where
the parasite is doing something (replicating or preparing to replicate); period of time where
there is indication where something is happening
-latent period: seemingly inactive period between exposure to an infection and subsequent
illness; in that period of time there is inactivity or seemingly inactive period of time where
potentially nothing is happening
-distinction between above 2 where incubation period, something is happening whether its
preparing to replicate or replication and latent period is a period of dormancy
-parasite virulence: capacity of a parasite to cause disease; how strong is it to effect to cause
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harm to the host; very virulent means can cause a lot of harm
-zoonotic infections: animal infections that can be transmitted to humans; source is
primarily an animal
-What are the main factors that influence the occurrence of a disease: three main factors
that have to e present at all times for a disease to occur and they are
hostenvironmentagent; the host meaning there has to be someone that has to be able to
be harmed; there has to be an agent that is something that can cause harm to the host; the
environment that promotes the exposure and allows it to happen
- host related factors can be age, gender, nutrition, immune/susceptible etc.
-agent can be anything that physical, biological, or chemical; all agents that can cause harm
-example of a cycle: a person develops severe cramps after drinking from a well located on a
cattle farm; the host is a person, the environment is the well water, the agent is perhaps
-modes of disease transmission: diseases can be spread primarily via two main routes and
they are direct and indirect transmission
direction transmission- from person to person; direct contact from humans
indirect transmission- though a common route/vector (e.g. contaminated air/water,
-portal of entry: entrance of the disease
dermal- through the skin e.g. fungus
ingestion- through the mouth e.g. E. Coli in water; drinking the water or eating
contaminated food
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