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ACCESS Human Biology.

Disease Causing Micro organisms.

Vera Harding.

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Aims. The student will be able to:• Define the meaning of infection.• Define communicable disease.• Differentiate between bacteria,

viruses, fungi, protoctista and parasites.

• Understand how infection is spread.• Discussion.

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Infection:• ‘The process by which organisms capable of

causing disease gain entry to the body and establish colonies’ (Youngson 1992).

• ‘The successful invasion, establishment and growth of micro-organisms in the tissues of the host. May be acute or chronic’ (Roper 1989).

• ‘Invasion of the body by harmful organisms (pathogens) such as bacteria, fungi or viruses’ (Roper 2003).

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Infectious (Communicable) Disease:• ‘Any disease that can be transmitted from

one person to another’ (Martin 2003).• ‘Diseases caused by organisms that can

spread directly from person to person’ (Younson 1992).

• ‘Disease caused by a specific, pathogenic organism and capable of being transmitted to another individual by direct or indirect contact’ (Roper 1989).

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Reason for health care workers to be concerned? YES!!• Infection poses a serious and continuing

threat to the public with 1 in 10 (10%) NHS hospital patients affected each year.

• This problem costs an estimated £1billion per annum.

• Hand hygiene is one of the most important indicators in reducing the risk of infection.

• (Pearce 2004).

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Bacteria.• A group of simple organisms.• Many bacteria are parasites.• Bacteria can survive for a long time as a

spore that protects them in a latent (inactive) state.

• Antibiotics cause damage to the spore wall.

• Only bacteria is denatured (killed) by antibiotics, therefore they should not be used to treat fungi or viruses.

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Bacteria - not always bad!• Commensal: Bacterium thrives - host

not affected, eg:– Staphylococcus aureus lives naturally on

skin, only causing problems if it gains entry into the body through broken skin, when it causes abscesses to form.

– Methicillin Resistant Staphylococcus Aureus lives in the noses and throats of general public. Dangerous only if entry is gained through broken or punctured skin.

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Bacteria - not always bad!

• Symbiotic: Bacteria is beneficial to both bacterium and host, eg:– Intestinal flora, (flora - colonisation of

micro-organisms) produces Vitamins B12 and K.

• Decomposition: Bacteria are involved in important processes of, eg:– The ‘Nitrogen Cycle’.

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Fungi.

• Simple organisms that include yeasts, moulds and mushrooms.

• Some fungi can cause disease in humans.• Some yeasts are a good source of Vit. B.• Many antibiotics are obtained from

moulds.• Fungi can cause rapid deterioration of

food, which can lead to disease.• Human skin (intact) prevents invasion.

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Viruses.

• Minute particles that can only replicate inside living cells.

• Viruses have specific targets, eg the cold virus targets the mucous membrane that lines the human nose.

• Viruses are specific to one host, eg, myxomatosis is fatal to rabbits, (it causes the mucous membranes to swell), but not harmful to humans.

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Protoctista.

• Single and multiple eukaryotic, (animal), cells. • Most are microscopic.• Protozoan and worms.• Amoeba ingest small particles of food.• Amoebic dysentery via contaminated water.

Eats intestinal flora.• Malaria via mosquito. Absorbs nutrients

through cell membranes.• Trichomoas vaginalis. Causes trichomoniasis

usually in vagina, sometimes in urethra or prostate. STI.

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Parasites.

• Parasites include any living thing that lives in or off another organism.

• The organism that the parasite survives on is called the ‘host’.

• Human parasites include;– Bacteria.– Fungi.– Viruses.– Worms.

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To cause disease pathogens: • Must be in sufficient numbers.• Must be virulent (powerful enough).• Must have a susceptible host.• Must enter body by appropriate

means. • Must have appropriate environment:

– Food.– Moisture.– Warmth.

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The pathogens enter the body by: • Inhalation: airborne spread (eg

colds, measles, sore throats, tuberculosis).

• Ingestion: through mouth via contaminated hands, infected food (eg salmonella).

• Inoculation: through the skin (eg MRSA).

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Infection is spread by:

• Airborne route: coughing and sneezing etc.

• Direct contact: hands, sex, blood etc .• Indirect contact: equipment, bedding,

food, (fomites) etc. • Vectors: flies, mosquitoes, rats, etc.• Waterborne.

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References.• Martin, E. (2003) Minidictionary for

Nurses. RCN: London. P135, 301, 320.• Pearce, L. (2004) Beating the Bugs.

Nursing standard. V.18.No.31.pp17-18.• Roper, N. (1989) Medical Dictionary.

Churchill Livingstone. London. P133, 143.• Thompson, D. (1996) • Youngson, R. (1992) Dictionary of

Medicine. Collins: Great Britain. P296, 313.