WEBVTT

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Infectious diseases can be caused

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by a variety
of different types of pathogens.

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These include:

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• bacteria - simple single-celled organisms

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• viruses - a protein shell or “capsid”,

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sometimes encased, enclosing
the genetic information the viruses need

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to replicate in animal or human cells.

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• fungal infections,
mostly involving single-cell forms

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such as athlete’s foot and yeasts

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but also multicellular molds.

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• parasites - this may include more complex
single-cell organisms (protozoa),

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but also multicellular organisms

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such as worms.

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In order to infect a human being

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the pathogens need to establish themselves
and in most cases reproduce

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on, or more often in, a human body.

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Pathogens may affect the entire body

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or just specific organs.

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The body’s immune system reacts
when pathogens invade.

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How effective the immune system is
in fighting off the pathogen

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depends on a number of factors,

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particularly
what type of pathogen is involved.

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So infectious diseases can differ widely
in terms of

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symptoms, progression
and duration.

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They may have mild symptoms
such as mild rhinitis

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but some may be fatal such as Ebola.

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Infectious diseases
can be transmitted from person to person,

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for example by touch or via droplets.

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Some pathogens are also spread
via other bodily fluids

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such as blood or sperm.

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But the infection may also be passed on

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via contaminated food or drinking water.

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Just how contagious
or infectious the disease is

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can vary significantly
from one type to another.

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Some can be passed on

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after spending longer periods
in the same room together,

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such as COVID-19,

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whilst intimate contact is needed
to be infected with others such as AIDS.

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In many cases

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there are effective drugs
to combat the pathogens:

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• antibiotics for bacterial infections

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• virostatics for viral infections

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• antimycotics for fungal infections,

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but there are many cases
where drugs cannot help.

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Some bacteria are becoming resistant
to some antibiotics currently available.

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Overall, infectious diseases

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are among the commonest causes of death
worldwide.

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In most cases the most effective way
to protect against them

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is good hygiene,
together with vaccinations in some cases.

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In short:

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Infectious diseases are caused by pathogens

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such as bacteria,

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viruses,

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fungi

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or parasites.

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They may cause a wide range
of symptoms or conditions.

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The body’s immune response
plays an important part

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in how the condition progresses.

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Although there are some effective drugs,

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infectious diseases are among
the commonest causes of death worldwide.

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There are a number of ways
of becoming infected,

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many of which can be avoided
by good hygiene.

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In some cases vaccination
is the most important protection.