Transcript File
Topic 6.6 Could the infections have been prevented? Specification- topic 6 • 10 Describe the major routes pathogens may take when entering the body and explain the role of barriers in protecting the body from infection, including the roles of skin, stomach acid, gut and skin flora. • 15 Explain how individuals may develop immunity (natural, artificial, active, passive). Barriers to infection Physical barriers and chemical defences which prevent entry into our body • Keratin (protein) of the skin and mucus and cilia in the mucous membranes, physical barrier • Lysozyme in tears, saliva, mucous break down bacterial cell walls causing them to burst. • Hydrochloric acid in the stomach kills most bacteria which enter with food • Skin and gut flora are harmless bacteria suited to the environment (in gut or on skin in spite of the salty sweat, urea and fatty acids – low pH) which can compete for food and space better than harmful bacteria. The harmless bacterial are better adapted to the conditions. In the gut they may help with digestion and secrete chemicals which harm the pathogens. Becoming actively immune • Active natural immunity – you are exposed to the pathogen and this causes an specific immune response. • You now have B and T memory cells to this antigen • Active Artificial immunity – you are vaccinated with an antigen and this causes an immune response. • You now have B and T memory cells to this antigen Passive immunity • You received antibodies across the placenta and in breast milk when you were a foetus and newborn. • You were able to fight any antigen you came in contact with at the time but this immunity only lasts for a few months • You had no immune response, therefore no memory cells made. Passive artificial immunity • You are given an injection of antibodies if you know you have been exposed to a pathogen but have not previously been vaccinated against it. • The disease is known to be very fast acting and deadly. • eg tetanus, rabies, ebola • This fights the pathogen immediately but does not give you long lasting immunity. • Q 6.38 Vaccinations The vaccine contains the antigens of the pathogen but will not harm you • Attenuated pathogen eg. measles, BCG, polio • Killed pathogen eg. whooping cough bacteria • Harmless form of toxin eg, tetanus • Antigen bearing fragment eg hepatitis B, meningitis C Challenges for vaccinations • Poor immune response eg. due to malnutrition • Antigenic changes • Due to mutations eg. flu • Due to different stages in a life cycle eg. malaria • Antigenic concealment • In cells eg. TB • In intestine eg. cholera • Boosters required for some vaccinations Herd immunity • When enough people are immunised the pathogen is less likely to be transferred. • Therefore there is less disease in the community. • Anyone who cannot have a vaccination for medical reasons is also protected. • Eg. for measles 95% of the population needs to be immunised for herd immunity. Successful vaccination programme – smallpox https://www.youtube.com/watch?v=jJwGNPRmyTI • Edward Jenner noted that cowpox sufferers never developed smallpox • In 1796 he inoculated a healthy boy with cowpox then injected him later with smallpox • The boy do not develop smallpox • Smallpox vaccination was developed and made compulsory in UK in 1853 Successful vaccination programme - smallpox • WHO targetted the eradication of smallpox • The disease was devastating and deadly • The vaccination was safe, effective and easy to administer • The pathogen was stable and did not mutate • Sufferers were easy to spot and isolate • Last case was in Somalia in 1977 • Declared eradicated in 1980 A stalled vaccination programme measles Deadly and debilitating in developing countries – leading cause of blindness, 2.6 million deaths per year prior to vaccination. Targeted by WHO for eradication. Effective, safe vaccine. 95% vaccination needed for herd immunity. A stalled vaccination programme measles However the uptake of the vaccine in developed countries has declined significantly. Measles seen as a “minor” illness. Vaccination fraudulently linked to several diseases eg. autism, bowel disease. Serious outbreaks of measles in central Europe eg 2008 Switzerland Herd immunity not achieved Vaccinations for TB? • Were you vaccinated against TB? • Vaccine introduced to UK in 1950s • Vaccine gave immunity to 80% of TB strains • Initially very effective • TB cases declined • Vaccine not given to all children in UK now. • Why? Vaccination for TB • TB now limited to very specific groups • - London or major cities • Born abroad in certain countries • Regular visitors (or close family members) to certain countries • Vaccine not as effective – resistant strains • Vaccinations only given to high risk groups Vaccine for HIV? • Not yet Would you vaccinate your children? • Do vaccines have side effects? • What are the risks? • Why do people overestimate the risks of vaccines? Specification- topic 6 • 10 Describe the major routes pathogens may take when entering the body and explain the role of barriers in protecting the body from infection, including the roles of skin, stomach acid, gut and skin flora. • 15 Explain how individuals may develop immunity (natural, artificial, active, passive).