Infection, Disease and Response

Communicable Disease

Several types of pathogens  Pathogens are micro-organisms that enter the body and cause disease  Cause communicable (infectious) disease - easily spread  Both plants and animals can be infected  Bacteria Very small cells - can reproduce quickly inside body  Can make you feel ill by producing toxins - damage cells and tissues  Viruses Not cells  Tiny, about 1/100th of the size of bacterium  Reproduce rapidly inside your body  Live inside cells and replicate themselves using cells' machinery to produce many copies of themselves  Cell will usually then burst, releasing new viruses  Protists Eukaryotes and most are single celled  Some protists are parasites  Live on or in other organisms and can cause them damage  Often transferred to organism by a vector  Doesn't get the disease itself  Fungi  Some are single-celled Others have a body - made up of hyphae   Hyphae can grow and penetrate human skin and surface of plants, causing disease  Can produce spores  Can be spread to other plants and animals  Pathogens can be spread in different ways Water  Some pathogens can be picked up drinking or bathing in dirty water  Air  Can be carried in the air and can then be breathed in Some airborne pathogens are carried in the air in droplets  Direct Contact  Can be picked up by touching contaminated surfaces   

Viral, Fungal and Protist Diseases

Viral Diseases Measles Spread by droplets from infected person's sneeze or cough Develop a red skin rash  Show signs of fever  Can be very serious  Can lead to pneumonia or a brain infection  Most people are vaccinated when young  HIV Spread by sexual contact, or by exchanging bodily fluids  Can happen when people share needles when taking drugs  Initially causes flu-like symptoms  Can be controlled with antiretroviral drugs - stop virus replicating  Attacks immune system  If immune system is damaged, it can't cope with other infections or cancers  Tobacco Mosaic Virus Affects many species of plants  Causes mosaic pattern on leaves  Parts of leaves become discoloured  Discolouration means plants can't carry out photosynthesis    Fungal Diseases Rose Black Spot  Causes purple or black spots to develop  Leaves can turn yellow and drop off Less photosynthesis so plant growth is affected  Spreads in water or by wind  Treated with fungicides and by stripping plant of affected leaves  Leaves need to be destroyed so fungus doesn't spread    Disease caused by protist Malaria Mosquitos are vectors - pick up malarial protist when they feed on infected animal  Every time mosquito feeds on another animal, it infects it by inserting protist into blood vessels  Causes repeating episodes of fever  Can be fatal  Spread of malaria can be reduced by stopping mosquitos from breeding Protected using insecticides and mosquito nets  

Bacterial Disease and Preventing Disease

Bacterial Diseases Salmonella Causes food poisoning  Infected people can suffer from fever, stomach cramps, vomiting and diarrohea  Caused by toxins that bacteria produce  Eating food that's contaminated  In the UK, most poultry are given a vaccination to control spread of disease Gonorrhoea Sexually transmitted infection  Passed by sexual contact Pain when urinating  Originally treated with penicillin  Strains of bacteria have become resistant to it  Prevent spread of it - people can be treated with antibiotics and should use barrier methods of contraception  Spread of diseases can be reduced or prevented Being hygenic - washing hands before preparing food or after sneezing  Destroying vectors - killed using insecticides or by destroying habitats so they can no longer breed  Isolating infected individuals - prevents spread of disease/passing on to someone else  Vaccination - can't develop infection and can't pass it onto someone else     

Fighting Disease

Body has features to stop things getting inside Skin  Acts as barrier to pathogens  Secretes antimicrobial substances which kill pathogens   Hairs and mucus  Trap particles that could contain pathogens  Trachea and bronchi  Secrete mucus to trap pathogens  Lined with cilia, which waft mucus up to the back of the throat where it can be swallowed  Stomach  Produces hydrochloric acid  Which kills pathogens  Immune system can attack pathogens  Immune system kicks in to destroy them  Most important part of immune system is white blood cells  WBC travel around blood and constantly check for microbes  Three lines of attack  White Blood Cells Consuming them - engulf foreign cells and digest them  Phagocytosis  WBC recognises pathogen is foreign  Engulfs pathogen  Produces lysozymes to digest pathogen  Pathogen is expelled by WBC  Producing antibodies Specific proteins on surface of them  When WBCs come across a foreign antigen, they will begin to produce antibodies to lock onto invading antigens - can be found and destroyed by other WBCs  Antibodies are specific to that type of antigen  Will not lock onto any other type of antigen  Produced rapidly and carried around body  WBCs can recognise antigens and will know how to rapidly produce antibodies to kill it  Person is naturally immune to pathogen  Producing antitoxins  Neutralise toxic chemicals released by pathogens   

Vaccination

When you're infected with a new pathogen, it takes WBCs a while to learn how to deal with it  Vaccinations involve injecting small amounts of dead or inactive pathogens  Carry antigens - cause body to produce antibodies to attack them  Memory cells can remember how to produce these antibodies and when to produce them  If you become infected, body can treat it quickly as it knows what antibodies to produce  Pros of vaccination Helped to control lots of communicable diseases  Large outbreaks of disease can be prevented  Even people who haven't been vaccinated are unlikely to catch it  Cons of vaccination Sometimes have bad reaction to a vaccine     Bad reaction are rare Vaccines don't always work  Sometimes they won't give immunity

Fighting Disease - Drugs

Painkillers are drugs - relieve pain - but don't tackle cause of disease/kill pathogens  Other drugs reduce symptoms  Antibiotics - kill bacteria causing the problem (doesn't kill body cells)  Different antibiotics kill different types of bacteria  Don't destroy viruses  Viruses reproduce using body cells - difficult develop drugs that don't destroy body cells  Use of antibiotics has greatly reduced, number of deaths caused by bacteria  Bacteria can mutate - cause them to be resistant to antibiotics  If you have an infection, some bacteria might be resistant to antibiotics Means when you treat the infection, only non-resistant strains of bacteria will be killed  Individual resistant bacteria will survive and reproduce Resistant strain could cause a serious infection - can't be treated by antibiotics  To slow down the rate of development of resistant strains - important to avoid over prescribing antibiotics  Important that you finish whole course of antibiotics and don't stop when you feel better Plants produce a variety of chemicals to defend themselves against pests and pathogens  Some of these chemicals - used as drugs to treat human disease or relieve symptoms  Aspirin Painkiller and lowers fever Developed from a chemical found in willow tree  Digitalis  Treats heart conditions  Developed from chemical found in foxgloves  Some drugs were extracted from micro-organisms  Fleming discovered penicillin which is mould that kills bacteria    Drugs are made on large scale in pharmaceutical industry - synthesised in labs - process may start with chemical from a plant   

Developing Drugs

Three main stages in drug testing  1. Preclinical Testing  Drugs are tested on human cells and tissues in lab  Can't use human cells and tissues to test drugs that affect whole or multiple body systems  2. Testing on live animals  Tests efficiency, to find about toxicity and best dosage  In Britain, a new drug must be tested in two different live mammals  Some think this is cruel - others believe it's the safest way to make sure drug isn't dangerous  3. Testing on human volunteers  Drug is tested on healthy volunteers (first)  Make sure it isn't harmful/have harmful side effects  At start of trial small dose is used and then gradually increased If results are good, drugs can be tested on people suffering from illness  Optimum dosage is found - most effective and has few side effects  Patients are given either drug or placebo - test how well it works  See difference drug makes - allows placebo effect  Clinical trials are blind  Patient doesn't know whether they're getting the drug or placebo  Often double-blind - neither patient or doctor knows until all results have been gathered  Doctors aren't influenced  Results f drug testing and drug trials aren't published until they've been through peer review  Helps to prevent false claims