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Causes of disease

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Learning outcomesStudents should understand the following

• Pathogens include bacteria, !iruses and fungi.

• "isease can result from pathogenicmicroorganisms penetrating any of an organism#sinterfaces with the en!ironment. $hese interfacesinclude the digesti!e

and gas-e%change systems.

• Pathogens cause disease by damaging the cellsof the host and by producing to%ins.

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&nfectious diseases

'pidemics ( widespread outbrea)s of diseasePandemics ( epidemics that spread

&nternationally.

Any microorganism that spreads disease iscalled a pathogen. $here are * types

+acteria e.g. salmonella, tuberculosis

irus e.g. &nuena, A&"S, measles

/ungi e.g. athletes foot, thrush

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&nitial infectionA microorganism must pass the bodies e%ternal

defences

S)in ( through a cut

0espiratory tract

"igesti!e system

rino-gential system

 $o help pre!ent entry the body has a number of

defences 2ucous layer that co!ers e%change surfaces

'nymes

Stomach acid

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Why do we feel ill?Pathogens colonise and reproduce in tissue and

body uids causing

Physical damage to cell structure

"isruption of cell metabolism and function

0elease of to%ins

Stimulation of the body#s immune system

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After infection3nce pathogens are inside they then attach to the

host cell !ia receptor binding protein molecules4ligands5 found in the microbial wall or !iral coat.

Pathogens enter by endocytosis or by producingenymes that breach the host cell membrane. $heymust then reproduce but this ta)es time.

 $he time period between infection and appearance

of signs and symptoms is called the incubationperiod.

&t is possible for an infected but otherwiseapparently healthy person to pass on an infection (

carrier.

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 $o%ins2any bacterial pathogens produce to%ins

'%oto%ins ( secreted by or lea) from bacteriaEscherichia Coli - e%oto%ins a6ect lining of intestines

and cause diarrhoea.

Clostridium tetani ( e%oto%ins a6ect ner!e cellsresulting in spastic paralysis 4loc)7aw5

'ndoto%ins ( comple% compounds released whenbacterial cell dies. $hey are pic)ed up by macrophages 4type of white

blood cell5 and cause them to produce proteins thatalter the body#s temperature -regulatingmechanisms, resulting in a fe!er. $hese proteins also

cause wea)ness and aching.

$

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 $ransm ss on opathogensPathogens can infect an indi!idual in a number

of ways

Air-borne infection

e.g. chic)enpo%, inuena, $+

Water-borne infectione.g. Vibrio cholerae and Escherichia coli

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 pathogens

/ood-borne infectione.g. salmonella and typhoid

"irect contact infectione.g. athletes foot 4fungal5

Se%ually transmitted diseases e.g. Syphilis4bacterial5 genital herpes, 8& 4!iral5

Animal !ectorse.g. malaria

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Learning outcomesStudents should understand the following

• Pathogens include bacteria, !iruses and fungi.

• "isease can result from pathogenicmicroorganisms penetrating any of an organism#sinterfaces with the en!ironment. $hese interfacesinclude the digesti!e

and gas-e%change systems.

• Pathogens cause disease by damaging the cellsof the host and by producing to%ins.