INFECTION & RESPONSE TOPIC 3 CHANTELLE

• Communicable (Infectious) Diseases


  Illnesses that spread from one person to another or from an animal to a person, or from a surface or a food
• Pathogens


  • Viruses
  • Bacteria
  • Protists
  • Fungi
• Bacteria


  • Reproduce rapidly and can affect the host by releasing toxins, these damage tissues and make us feel unwell
• Viruses


  • Need a host to survive and reproduce
• Fungi


  • Grow on living tissue, some are single-celled and others have a body made of hyphae
• Protists


  • Eukaryotic organisms some of them are parasitic, that live on or inside the host
• Pathogens can be spread by a range of transmission methods
• Bacteria produce toxins that damage cells and viruses are replicated inside cells
• Antibiotics are effective against bacteria but not viruses
• Viruses


  Do not fulfil the 7 life processes, therefore, they are not usually classified as living organisms
• Virus reproduction


  1. Inserting their genetic material into host cells

  2. Creating new protein capsules to build new viral particles

  3. Host cell may burst open releasing the viral particles which can go on to infect other cells

  
• Measles


  Highly contagious and a potentially serious viral infectious disease that can be fatal if complications arise
• HIV


  Virus that can eventually lead to Acquired Immunodeficiency Syndrome (AIDS)
• Tobacco Mosaic Virus


  First virus to be isolated by scientists, a widespread plant pathogen that infects about 150 species of plants including tomato plants and cucumbers

  
• Bacteria


  • Not all bacteria are harmful (so not all bacteria are pathogens)
  • Bacteria on the skin act as competitors to harmful pathogens
  • Bacteria in the large intestine digest substances we can't in food (such as cellulose) and provide essential nutrients (such as Vitamin K)
• Bacterial pathogens


  Produce toxins that cause damage to cells and tissues directly
• In certain optimum conditions, some bacteria can reproduce rapidly (with the fastest being once every 20 minutes for some species of coli)</b>
• Optimum conditions for rapid bacterial reproduction usually involve warmth, moisture and a supply of nutrients

  
• Salmonella food poisoning


  Spread by bacteria ingested in food, or on food prepared in unhygienic conditions
• Gonorrhoea


  Sexually transmitted disease (STD) – these diseases are also called sexually transmitted infections (STI)

  
• Fungal diseases


  Few fungal diseases that affect humans, one example is athletes' foot. This is spread by contact with surfaces that have been touched by an infected person, such as shower room floors
• Fungi


  • Often the fungus is unicellular, as in the case of yeast, but can have a body made up of thread-like structures called hyphae
  • The hyphae can grow and penetrate the surface of plants and animals causing infections
  • The hyphae can produce spores, which can spread the infection to other organisms
• Rose black spot


  Fungal disease of plants where purple or black spots develop on leaves, which often turn yellow and drop early. It affects the growth of the plant as photosynthesis is reduced. It is spread in the environment by water or wind
• Protists


  Diverse group of eukaryotic and usually unicellular organisms. Only a small number of protists are pathogenic, but the diseases they cause are often serious. Often need a vector to transfer from one host to the next
• Malaria


  The pathogens that cause malaria are protists, they have a complex life cycle but can infect red blood cells in humans. The malarial protist has a life cycle that includes the mosquito as a vector. Malaria causes recurrent episodes of fever and can be fatal in certain instances. The spread of malaria is controlled by preventing the vectors, mosquitos, from breeding and by using mosquito nets

  
• Non-specific defences of the human body against pathogens


  • The skin
  • The nose
  • The trachea and bronchi
  • The stomach

  
• Immune system


  Highly complex, with white blood cells being the main component. Once a pathogen has entered the body the role of the immune system is to prevent the infectious organism from reproducing and to destroy it

  
• Phagocytosis


  1. Phagocytes engulf and digest pathogens, this can be non-specific or helped by antibodies which cause agglutination (clumping) of pathogens

  2. The phagocyte surrounds the pathogen and releases enzymes to digest and break it down to destroy it
• Antibodies


  1. shaped proteins – each individual has the potential to make millions of different types of antibodies, each with a slightly different shape. The aim of antibody production is to produce the antibody that is specific (complementary) to the antigens on the surface of the pathogen

  
• Memory cells


  Lymphocytes that remain in the body after an initial infection with a particular pathogen; they produce the specific antibodies against its antigens so that if you get infected by the same pathogen again in the future (and the antigens are the same) you can produce antibodies much quicker against it before its numbers increase and it can cause damage to the tissues of the body

  
• Antitoxins


  Antibodies produced by lymphocytes against toxins produced by pathogens (usually bacteria), they neutralise the effects of the toxin

  
• Vaccination


  Involves exposing an individual to the antigens of a pathogen in some form, triggering an immune response which results in the formation of memory cells which can make antibodies against it. If a vaccinated individual is infected with the pathogen, they can destroy it before they become infectious

  
• If a large number of the population are vaccinated, it is unlikely that an unvaccinated individual will become infected with the pathogen. This is the principle behind the idea of herd immunity

  
• Active immunity


  Comes from the body creating antibodies to a disease either by exposure to the disease (natural) or by vaccination (artificial)

  
• Passive immunity


  Comes from antibodies given to you from another organism, for example in breast milk

  
• Antibiotics, such as penicillin, are medicines that help to cure bacterial disease by killing infective bacteria inside the body
• Antibiotics will not work against viruses, as viruses reproduce inside cells. It is difficult to develop drugs that kill viruses without also damaging the body's tissues
• Painkillers and other medicines are used to treat the symptoms of disease but do not kill pathogens (eg. ibuprofen can reduce pain and inflammation)
• Antibiotic resistance


  Antibiotics have been overused and antibiotic resistance has developed in many different types of bacterial species. Bacteria, like all organisms, have random mutations in their DNA. One of these mutations may give them resistance to an antibiotic. If an organism is infected with bacteria and some of them have resistance, they are likely to survive treatment with antibiotic. The population of the resistant bacteria will increase
• Penicillin


  The first antibiotic to be discovered