Transcript pathogen
Infection and Disease Cellular and Non-cellular Pathogens S Disease S A disease is any change that impairs the function of an individual in some way. S Diseases may be inherited or caused by many other factors. S An infectious disease is one caused by a pathogen. Pathogens S A pathogen may be a: S Multicellular organism, eg. fungus and worm S Single-celled organism, eg. eukaryotes such as protozoan or prokaryotes such as bacterium S Non-cellular agent, eg. virus and prion Transmission of Pathogens S Some diseases can be transmitted from person to person because the pathogenic organism or agent causing the disease can be transmitted. S Infective agents can be transmitted from one host to another by: S Direct contact S Droplets in air breathed or sneezed out by an infected person S Sexual contact S Contaminated food or water S A carrying vector, eg. rats carrying fleas S An injecting vector, eg. mosquitoes carrying malarial parasites S Injection with infected needles and syringes Bacteria S Are prokaryotic organisms lacking a nuclear membrane. S Have cell walls made of carbohydrates, lipids, amino acids and sometimes other substances. S Contain a single circular molecule of DNA. S Can be classified by shape, eg: S coccus (round) S bacillus (rod shaped) S spirochaete (spiral) S This often relates to their naming – eg. Staphylococcus aureus are a round-shaped bacteria Bacteria ☢ Can be classified by their metabolic characteristics ☢ Reproduce exponentially and quickly (as little as 20 minutes) in favourable conditions. S Can have special features, including a flagellum, capsule or spore. S Gram positive bacteria have a thick peptidoglycan layer S Gram negative bacteria have a thin peptidoglycan layer and a lipopolysaccharide wall, which makes them more virulent Bacteria S Treatment of bacteria diseases: S Chemotherapy (term used when a disease is treated with chemicals). S Antibiotics/antimicrobials S Some drugs are: S narrow-spectrum and act against a limited variety of microorganisms; S broad-spectrum and act against many different kinds of pathogens. S Treatment must be carefully administered as bacteria can become antibiotic resistant. Eg. Golden Staph Fungi, Yeast & Protozoa S Fungi, yeasts and protozoa are all eukaryotic organisms that can cause disease. S Fungi S Decompose dead organic matter S Spread readily as spores S Bacterial antibiotics do not act against fungi. Antifungal ointments and oral preparations are used to treat fungal infections. Fungi, Yeast & Protozoa S Yeasts are unicelluar fungi. S Protozoa are single-celled organisms. S Examples include Plasmodium, Giardia and Amoeba Arthropods and worms S Arthropods S Are generally parasitic but are not necessarily pathogenic S Include head lice and body lice. S Worms S May be parasitic but are not necessarily pathogenic S Include Echinococcus granulosis, a pathogenic hydatid tapeworm, which normally lives in dog intestines but which can spend part of its life cycle in human host tissues. S Include parasitic nematode worms that live in plant tissue. Viruses S Viruses: S Are extremely small S Have a protein coat S Have a core of either DNA or RNA S Reproduce only after entering a host cell and using its components S Are parasitic and pathogenic S Can infect humans, other animals, plants and bacteria Viruses S How do viruses affect a host cell? S Viruses must enter a host cell to reproduce. S They use components of the host cell as a source of energy and material to make new viruses and ultimately destroy the host cell. S Different kinds of viruses may reproduce in slightly different ways. Types of viruses Adenovirus Retrovirus S DNA virus S RNA virus S Utilises host cell ribosomes to replicate S S Does not possess a viral envelope Uses reverse transcriptase to create DNA which is incorporated into the host DNA S Has a viral envelope Viruses S Antiviral drugs S Because viruses enter host cells, it is difficult to inhibit the reproduction of a virus without interfering with the metabolism of the host cell. S Some antiviral drugs have been developed that specifically act on enzymes important to the virus without damage to the host cell. Viroids and Prions S Viroids: S Contain very short pieces of naked RNA S Are important as plant pathogens S Are known to infect plants including potatoes, tomatoes and grapevines. S Completely dependent on the host cell for replication. S S S S Prions: Do not contain genetic material Are an abnormal and infectious form of protein Cause a range of brain diseases including spongiform encephalopathy. S No treatment is available for individuals infected with abnormal prions.