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DiseaseSarah Jones

What is a healthy organism?

Health is the wellbeing of the organism. All our body functions, which are under the control of our genes, work together to maintain health.

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Disease is any condition that adversely affects the function of any part of a living thing.

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An infectious disease is one that is caused by an organism and that can be transferred from one person to another. The transfer may be directly from person to person, or it may be carried out by a vector, such as a blood-sucking insect.

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Examples of infectious diseases are colds, influenza, chicken pox, herpes and measles.

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Hepatitis C Virus

Non-infectious diseases are diseases that are not due to disease-causing organisms. They include genetic diseases, such as Down syndrome, haemophilia, and those that are related to lifestyle or environment, such as cardiovascular disease and skin cancer.

Agents of Disease

PathogensOrganisms are called pathogens when they cause disease. To cause disease, organisms need the right conditions to multiply and be transmitted.

Ebola

An infectious disease is caused by a pathogen and can be passed from one organism to another.

How are diseases spread?

• Airborne• Contact• Faeces• By other organisms• The Asian tiger mosquito is responsible for the

transmission of dengue and yellow fever plus 20 other viral diseases.

Pathogens and EpidemicsDuring the Middle Ages waves of infectious diseases such as cholera and plague swept through Europe.

Plague victims being blessed by a priest

MacroparasitesMacroparasites are large parasites that can be seen with the naked eye. They may be internal or external parasites. Examples of internal include, tapeworms, roundworms and flukes. External parasites include lice, ticks and fleas.

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Immune Response – The Body's Response to Micro-Organisms

Flu Pneumonia German Measles

Bodies Defence1. Physical (skin and mucous) 2. Nonspecific defensive cells (phagocytes,

white blood cells, inflammation and fever)3. Immune Response (lymphatic system-

recognition of foreign cells)

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Our bodies contain very large numbers of bacteria (approximately 15% of your body weight) and many of those in the intestine are essential for our wellbeing (microflora).

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Defence Barriers• Skin• Mucous membranes• Cilia• Chemical barriers• Specific response -

Immune response

Defence Adaptations - Non-specific responses• Inflammation response• Phagocytosis• Sealing off the pathogen

Electron Micrograph of a Macrophage Phagocytosis of E. coli

The Immune ResponseThe key to a healthy immune system is its remarkable ability to distinguish between the body’s own cells (self) and foreign cells (nonself).

www.niaid.nih.gov

The body’s immune defenses normally coexist peacefully with cells that carry distinctive "self" marker molecules. But when immune defenders encounter cells or organisms carrying markers that say "foreign," they quickly launch an attack.

Anything that can trigger this immune response is called an antigen. An antigen can be a microbe such as a virus, or even a part of a microbe.

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Tissues or cells from another person (except an identical twin) also carry non-self markers and act as antigens. This explains why tissue transplants may be rejected.

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