Disease and Defence

• Pathogens are microorganisms that cause infectious diseases.
• Pathogens can be spread in the air, or through water droplets. They can also be spread directly in water and direct contact between individuals.
• Malaria is caused by a single celled protist called Plasmodium. To prevent malaria mosquito repellents, nets, insecticides and biological control are used.
• Chlamydia is caused by the bacteria Chlamydia trachomatis. Can be treated with antibiotics, and can be prevented by use of condoms.
• HIV (Human Immunodeficiency Virus) is a virus that attacks the immune system. It often leads to AIDS. HIV is spread via infected bodily fluids. Can prevent by using a condom, and using disposable gloves when handling blood.
• Phagocytes have a flexible membrane and contain lots of enzymes. This enables them to engulf foreign cells and digest them.
• Lymphocytes recognise antigens on pathogens as foreign and produce antibodies to lock onto the invading cells. The antibodies produced are specific to the antigen. The lymphocytes divide many time by mitosis. Memory cells are produced which can produce antibodies quickly if the same antigen is encountered again.
• Firstly, a mouse is injected with a chosen antigen, and its immune system is stimulated to produce antibodies. Lymphocytes dont divide easily so the spleen cells are fused with human cancerous white blood cells called myeloma cells to form hybridoma cells which divide indefinitely. These can be cloned.
• A vaccine contains weakened or dead forms of a disease causing organism. When given into the body, the immune system responds by producing antibodies. If the person comes into contact with the real disease later, their immune system will already know how to fight it off.
• Monoclonal antibodies can target cancer cells, as they bind to the tumour markers. They can help deliver chemotherapy directly to the cancer cells, which decreases side effects.
• Immunoassays- Monoclonal antibodies are made for the specific antigens on disease causing agents such as Chlamydia Trachomatis, HIV and plasmodium. This antibodies are labelled with dyes that glow fluorescent under UV light, and added to bodily fluids. The extent of labelling detected indicates the extent of the infection.
• Tissue Typing- Monoclonal antibodies can prevent rejection. They combine with and inactivate helper T cells. Without these, the lymphocytes that produce antibodies against the transplanted organ won't work.
• Monitoring Malaria- Monoclonal antibodies specific to Plasmodium antigens are used to test blood samples. This detects Plasmodium living or dead. It can show the effectiveness of anti-malarial drugs. For example, if the persons blood contains Plasmodium but they are not suffering malaria, the drug works.
• Cancer diagnosis and treatment- Some cancerous cells have antigens called tumour markers. Monoclonal antibodies can bind and clump these together making it easy to identify a cancerous tumour. They can also carry anti-cancer drugs directly to these cells.
• Chlamydia causes infertility in adults, conjunctivitis and lung problems in babies. Treatment includes antibiotics such as tetracycline.
• Malaria destroys red blood cells causing fever. Treatment includes anti-malarial drugs such as paludrine. Malaria is spread by female mosquitos so releasing large numbers of infertile male mosquitos can also reduce malaria.
• AIDS infects lymphocytes leading to lack of immunity against other infections. Antiviral drugs must be taken for life. It can also be spread by blood to blood contact so disposable gloves must be used.
• Preclinical trials- testing on human cells grown in laboratories, then animals and finally healthy human volunteers.
• Clinical Trials- Small groups of patients. Blind trial- patients don't know if they have been given the drug or placebo but the doctors know. Double Blind trial- both the patients and the doctors don't know if the patients have been given the drug or placebo, but the researchers know.
• Once the microorganisms have been destroyed, all the clones of lymphocytes die off except a few. These are called memory cells. If the same microbe is encountered again antibodies will be produced faster and in large numbers, destroying microbes before symptoms are felt.
• Vaccinations are a dead, attenuated, or part of the microbe with the antigen on.
• AIDS (Acquired Immune Deficiency Syndrome)
• Some bacteria have become resistant to antibiotics. This could be because of the use of antibiotics in animal feed, and over-prescription for humans. MRSA control measures could include: hand washing, thorough cleaning of hospital wards, use of alcohol gels and MRSA screening
• Some conditions can be prevented by good hygiene, clean water, improved diet, and vaccination. Some can be treated by drugs such as antibiotics.
• Bacterial cells consist of a cell wall, cell membrane and cytoplasm, no distinct nucleus so DNA floats free. Some also have a flagellum. Viruses consist of a number of genes surrounded by a protein coat.
• Types of organisms which can cause communicable diseases: Viruses, bacteria and fungi
• Pathogens can also be spread through contaminated food, insects and body fluids.
• Plasmodium is spread via female mosquitoes of the genus Anopheles
• Blood clots seal wounds to prevent entry of microbes, and the community of microorganisms on the skin, the skin flora, make it difficult for pathogens to become established.
• For vaccinations- protecting children against diseases, epidemics can be prevented due to herd immunity (fewer people to pass on the disease), media campaigns run by organisations like the NHS encourage vaccinations.
• Against vaccinations- they don't always work, side effects such as swelling and seizures, media articles against vaccines- such as saying they can cause autism.
• Semi synthetic antibiotics- antibiotics from organisms modified in the lab to make them more effective. Synthetic antibodies- antibiotics created by chemists in a lab
• Antibiotics kill and prevent the growth of infecting bacteria, and many are produced naturally by fungi and other living organisms. Antibiotics don't destroy viruses. Viruses reproduce using your body cells, which makes it very difficult to develop drugs that don't kill body cells.
• Animal testing- cruel to test on animals as it may cause them pain and distress, safest way to make sure a drug isn't dangerous before given to humans and some believe its okay because scientists have to follow strict rules- properly look after animals and minimise discomfort.
• Alternatives to animal research- using computer models to predict the effects of drugs. As technology advances, new technology could supersede animal testing.
• Drug Trials- risk that the drug could have unexpected harmful effects, however trials are strictly regulated to guarantee everyone is as safe as possible. The benefits of collecting data which leads to the development of new and improved drugs usually outweigh the risks. #
• Tissue typing is used to identify the antigens produced by the potential donor and recipient.