Topic 3 : Infection and Response

• Pathogens are tiny microorganisms that cause communicable diseases.
• Bacteria Are tiny living cells that reproduce rapidly in the body and can produce toxins
• Viruses are not living cells, they reproduce rapidly and live inside human cells and use the cells to reproduce. the cell then bursts, releasing all of the new viruses. The cell damage is what causes you to feel ill
• Protists are eukaryotic cells and most are single celled. Some protists are parasites, and live on or inside other organisms and can cause damage. They are often transferred through a vector, which doesn't get the disease itself.
• Some Fungi are single-celled, others have a body made up of hyphae, these can grow and penetrate human skin and the surface of plants, causing disease. These can also produce spores, which can spread to other plants and animals
• Some pathogens can be picked up by drinking or bathing in dirty water like cholera, a bacterial infection, spread by contaminated water
• Pathogens can be carried in the air and can be breathed, some are carried in droplets through the air produced when you cough or sneeze, like the influenza virus
• Some pathogens can be picked up by touching contaminated areas, such as the skin, like athletes foot, a fungus spread by touching the same area as an infected person
• Measles is a virus spread by droplets from sneezes or coughs. Symptoms can be a red skin rash, and a fever. Measles can be fatal with complications, such as causing pneumonia. Most people are vaccinated against this
• HIV is a virus spread by sexual contact, or the exchange of bodily fluids. It initially causes flu-like symptoms for several years, during this time, it can be treated with antiretroviral drugs, these stop the replication of the virus and the development of AIDS. The virus attacks the immune cells. If the bodies immune system is badly damaged (Immunosuppression), it can't cope with other infections or cancers, at this stage it is known as AIDS.
• Tobacco mosaic virus (TMV) is a virus that causes yellowing of leaves and discolouration of the stems. This discolouration means the plant can't carry out photosynthesis as well, restricting growth.
• Rose black spot is a fungus that causes purple or black spots to develop on the leaves of the plant, they can then turn yellow and fall off. This means photosynthesis can't happen, preventing photosynthesis. It spreads through water or wind.
• Malaria is caused by a protist. Part of it's life cycle takes place in a mosquito, the vector. These pick up malaria when feeding on infected Animals, and every time it feeds on another animal, it infects by inserting the the protist into the animals bloodstream. Malaria causes repeating episodes of fever and can be fatal. Methods of preventing infection is use of insecticides and mosquito nets
• Salmonella is a bacterial disease that causes food poisoning, infected people can suffer from fever, stomach cramps, vomiting and diarrhoea. These are caused by the toxins released by the bacteria. It is caused by consuming food infected by the bacteria. eg chickens with salmonella whilst alive, or eating food by being prepared in unhygienic conditions
• Gonorrhoea is a bacterial STD (sexually transmitted disease). Symptoms include pain when urinating or a thick yellow or green discharge from the penis or vagina. It was originally (and in some cases is)treated with penicillin however this has become difficult as certain strains have become resistant. To prevent infection, barrier protection should be used
• Spread of disease can be reduced by being hygienic, destroying vectors, isolating infected individuals, and vaccinating people
• The human body's non-specific defences are the skin, hairs and mucus, cilia, and hydrochloric acid in the stomach.
• White blood cells engulf foreign cells and digest them. This is called phagocytosis
• Every invading pathogen has unique molecules called antigens. When lymphocytes come across them, they will start producing proteins called antibodies to lock onto antigens so it can neutralise and mark the invading antibody
• Antitoxins are produced to counteract toxins produced by invading bacteria
• When you are infected with a new pathogen, it takes white blood cells a few days to produce antibodies. Vaccinations inject small amounts of dead or attenuated (weakened) pathogens into the body. These cause your white blood cells to produce antibodies. The pathogen is harmless.
• If live pathogens of the same type invade the body after a vaccination, the white blood cells can rapidly mass-produce antibodies to destroy them
• Pros of vaccination are that they help control communicable diseases that were once incredibly common through herd immunity. Big outbreaks of diseases are called epidemics, these can be prevented if a large amount of the population are vaccinated against the disease.
• Cons of vaccination are that they don't always grant full immunity, and very rarely, people can have bad reactions to them
• Some drugs, painkillers, only relieve pain and symptoms, and don't tackle the underlying cause, allowing the body's defences to deal with it
• Other drugs, antibiotics, actually kill or prevent the growth of bacteria causing the problem. Different antibiotics kill different types of bacteria, so it is important to know which type of bacteria is causing the problem. However, antibiotics only work against bacteria, not against viruses.
• Bacteria can mutate, becoming resistant to antibiotics, this means when people are treated with antibiotics, it will only kill the non-resistant strains, leaving the resistant strains to reproduce. This causes a serious infection not treatable with antibiotics. to prevent this, doctors must avoid over-prescribing antibiotics
• In preclinical testing, drugs are tested on cells and tissues in a laboratory test for toxicity and efficacy
• The next step of preclinical trials are testing on animals, again to further test efficacy (how well the drug works) and toxicity (how safe it is) and to find the optimum dosage. UK law states it must be tested on 2 live mammals
• The clinical trial is where the drug is tested on humans. First, on healthy volunteers, to make sure there are no harmful side effects, this is using a very low dosage, gradually increasing it. then it is tested on unhealthy patients, to find the optimum dosage. To test how well the drug works, patients are randomly assorted into 2 groups, on given the drug, and the other, a placebo, so the effects can be directly seen, this is called a double-blind trial.
• Monoclonal antibodies are identical antibodies, produced by B-lymphocytes. They are produced from lots of clones of a single white blood cell, this means all are identical and will only target one specific protein antigen.
• Monoclonal antibodies are are produced by injecting a mouse with the chosen antigens, and then the B-lymphocyte fuses with a tumour cell to produce a hybridoma, which divides quickly to produce lots of clones that produce the monoclonal antibodies, which can be collected, and purified.
• Monoclonal antibodies can be used in pregnancy tests, this works by having monoclonal antibodies designed to bind to the hormone HCG, only excreted in the urine of a woman who is pregnant, these antibodies are bound to a special blue dye, the test strip has more antibodies stuck to it(so they can't move). If a woman is pregnant and urinates on the stick, the hormone binds to the antibodies and move up the stick, carrying the hormone with it, the beads and hormone bind to the antibodies on the display window, turning it blue.
• Different cells in the body have different antigens on the cell surface, so monoclonal antibodies can be made to bind to specific cells in the body, allowing them to be identified. Cancer cells have a different antigen to normal cells called tumour markers, and monoclonal antibodies can be made to bind to these and destroy the cancer cells, without damaging the body's cells.
• In laboratories, monoclonal antibodies can be used to bind to hormones and other chemicals in the blood to measure their levels. To test blood samples for certain pathogens and locate a specific molecule on a cell or in a tissue
• Monoclonal antibodies can cause side effects however, such as fever, vomiting and low blood pressure, this means they are not as widely used as first intended
• Plants need mineral ions, if they are lacking certain ones, they will suffer deficiency symptoms
• Nitrates are needed to make proteins and therefore growth, so a deficiency can result in stunted growth
• Magnesium is needed for making chlorophyll, and therefore photosynthesis, a deficiency in which causing chlorosis, yellow leaves and stunted growth.
• Potassium is needed for photosynthesis and respiration, and a deficiency causes yellow / purple leaves.