Infection and Response

• Pathogens


  Microorganisms that cause infectious disease
• Types of pathogens


  • Viruses
  • Bacteria
  • Protists
  • Fungi
• Pathogens


  • May infect plants or animals
  • Can be spread by direct contact, by water or by air
• Bacteria and viruses


  May reproduce rapidly inside the body
• Bacteria


  May produce poisons (toxins) that damage tissues and make us feel ill
• Viruses


  Live and reproduce inside cells, causing cell damage
• Measles


  • A viral disease showing symptoms of fever and a red skin rash
  • A serious illness that can be fatal if complications arise
• Most young children are vaccinated against measles
• Measles virus


  Spread by inhalation of droplets from sneezes and coughs
• HIV


  • Initially causes a flu-like illness
  • Unless successfully controlled with antiretroviral drugs the virus attacks the body's immune cells
  • Late stage HIV infection, or AIDS, occurs when the body's immune system becomes so badly damaged it can no longer deal with other infections or cancers
• HIV


  Spread by sexual contact or exchange of body fluids such as blood which occurs when drug users share needles
• Tobacco mosaic virus (TMV)


  • A widespread plant pathogen affecting many species of plants including tomatoes
  • Gives a distinctive 'mosaic' pattern of discolouration on the leaves which affects the growth of the plant due to lack of photosynthesis
• Salmonella food poisoning


  • Spread by bacteria ingested in food, or on food prepared in unhygienic conditions
  • In the UK, poultry are vaccinated against Salmonella to control the spread
  • Fever, abdominal cramps, vomiting and diarrhoea are caused by the bacteria and the toxins they secrete
• Gonorrhoea


  • A sexually transmitted disease (STD) with symptoms of a thick yellow or green discharge from the vagina or penis and pain on urinating
  • Caused by a bacterium and was easily treated with the antibiotic penicillin until many resistant strains appeared
  • Spread by sexual contact
  • The spread can be controlled by treatment with antibiotics or the use of a barrier method of contraception such as a condom
• Rose black spot


  • A fungal disease where purple or black spots develop on leaves, which often turn yellow and drop early
  • Affects the growth of the plant as photosynthesis is reduced
  • Spread in the environment by water or wind
  • Can be treated by using fungicides and/or removing and destroying the affected leaves
• Malaria


  • The pathogens that cause it are protists
  • The malarial protist has a life cycle that includes the mosquito
  • Causes recurrent episodes of fever and can be fatal
  • The spread of malaria is controlled by preventing the vectors, mosquitos, from breeding and by using mosquito nets to avoid being bitten
• Immune system


  If a pathogen enters the body it tries to destroy the pathogen
• Ways white blood cells help defend against pathogens


  • Phagocytosis
  • Antibody production
  • Antitoxin production
• Vaccination


  • Involves introducing small quantities of dead or inactive forms of a pathogen into the body to stimulate the white blood cells to produce antibodies
  • If the same pathogen re-enters the body the white blood cells respond quickly to produce the correct antibodies, preventing infection
• Antibiotics


  • Medicines that help to cure bacterial disease by killing infective bacteria inside the body
  • It is important that specific bacteria should be treated by specific antibiotics
• The use of antibiotics has greatly reduced deaths from infectious bacterial diseases
• The emergence of strains resistant to antibiotics is of great concern
• Antibiotics cannot kill viral pathogens
• Painkillers and other medicines


  Used to treat the symptoms of disease but do not kill pathogens
• It is difficult to develop drugs that kill viruses without also damaging the body's tissues