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Health and Disease Objectives To understand what is meant by the terms health, disease, pathogen and parasite What is Health? WHO definition of health: A state of complete physical, mental and social well being NOT merely an absence of disease Well integrated into society Suitably housed with sanitation Free from disease Healthy Individual Well fed with a balanced diet Happy, positive outlook Able to perform normal Physical and mental tasks What is Disease? Disease is a malfunction of body or mind which causes symptoms that could be physical, mental or social Pathogens and parasites • A Pathogen is a disease causing organism which lives by taking nutrition from a host and causing damage in the process. • A Parasite is an organism that lives in (internal) or on (external) another host organism causing it harm. • All pathogens are parasites but not all parasites are pathogens For Example: A head louse is an external parasite but is not a pathogen A tape worm is an internal parasite but is not a pathogen Norovirus is an internal parasite and a pathogen Disease can be caused by: • Living organisms – infectious diseases E.g. Tuberculosis • Age induced E.g. Alzheimer's • Inherited E.g. Cystic Fibrosis • Environment E.g. Allergies Disease causing organisms (pathogens) Bacteria E. coli Streptococcus Salmonella MRSA Staphylococcus Bacteria Are small cells that reproduce rapidly (every 20 minutes in the right conditions). They act by releasing toxins or damaging cells. e.g. Vibrio cholerae (cholera), Mycobacterium tuberculosis (TB) Fungi e.g. Athletes Foot Tinea pedis Yeast E.g.Thrush (Candida albicans) Fungi • Can live in the skin and send out branching structures called hyphae. These are reproductive structures which release spores which can cause redness and irritation. • E.g. Tinea (athlete’s foot and ringworm) Ringworm – not actually caused by a worm! Viruses HPV Influenza HIV Meningitis Norovirus Herpes Viruses Cause many diseases by invading cells and altering genes. They then cause the cell to produce more copies of the virus. The host cell eventually bursts releasing many new viruses. E.g. Tobacco mosaic virus (affects many plants) Electron microscope image of TMV Healthy and infected plants TMV is made up of a helix of over 2000 protein subunits Protoctista These are animal like organisms which enter host cells and feed on their contents. Plasmodium falciparum causes malaria Amoeba (Entamoeba histolytica) causes amoebic dysentery Giardia lamblia is the most common cause of diarrhea in North America