Topic Three - Infection and Response

• Pathogens are microorganisms that cause infectious disease. Pathogens may be viruses, bacteria, protists or fungi. They may infect plants or animals and 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 is a viral disease showing symptoms of fever and a red skin rash. Measles is a serious illness that can be fatal if complications arise. For this reason most young children are vaccinated against measles. The measles virus is 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 is spread by sexual contact or exchange of body fluids such as blood which occurs when drug users share needles.
• Tobacco mosaic virus (TMV) is a widespread plant pathogen affecting many species of plants including tomatoes. It 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 is 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 is a sexually transmitted disease (STD) with symptoms of a thick yellow or green discharge from the vagina or penis and pain on urinating. It is caused by a bacterium and was easily treated with the antibiotic penicillin until many resistant strains appeared. Gonorrhoea is 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 is a fungal disease 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. Rose black spot can be treated by using fungicides and/or removing and destroying the affected leaves
• The pathogens that cause malaria are protists. The malarial protist has a life cycle that includes the mosquito. Malaria 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.
• 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, such as penicillin, are 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. However, the emergence of strains resistant to antibiotics is of great concern
• Antibiotics cannot kill viral pathogens. Painkillers and other medicines are 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.
• Traditionally drugs were extracted from plants and microorganisms. • The heart drug digitalis originates from foxgloves. • The painkiller aspirin originates from willow. • Penicillin was discovered by Alexander Fleming from the Penicillium mould.
• Most new drugs are synthesised by chemists in the pharmaceutical industry. However, the starting point may still be a chemical extracted from a plant.
• New medical drugs have to be tested and trialled before being used to check that they are safe and effective. New drugs are extensively tested for toxicity, efficacy and dose.
• Preclinical testing is done in a laboratory using cells, tissues and live animals. Clinical trials use healthy volunteers and patients. • Very low doses of the drug are given at the start of the clinical trial. • If the drug is found to be safe, further clinical trials are carried out to find the optimum dose for the drug. • In double blind trials, some patients are given a placebo
• The skin acts as a barrier to pathogens, it also secretes antimicrobial substances which kill pathogens.
• Hairs and mucus in your nose trap particles that could contain pathogens
• The trachea and bronchi secrete mucus that traps pathogens, they are lined with cilia; hairlike structures which waft the mucus up the back of the throat where it can be swallowed.
• the stomach produces hydrochloric acid, which kills pathogens.
• Phagocytosis is when whiteblood cells engulf foreign cells and digest them.
• Every invading pathogen has unique antigens on its surface. When some types of white blood cells come across foreign antigens they will start to produce proteins called antibodies to lock onto the invading cells so that they can be found and destroyed by other white blood cells. These antibodies are specific to that type of antigen and won't lock on to any others.
• Antibodies are produced rapidly and carried around the body to find all similar bacteria or viruses. If the person is infected with the same pathogen again, the white blood cells will rapidly produce the antibodies to kill it; the person is immune to that pathogen.
• Antitoxins counteract toxins produced by the invading bacteria.
• Vaccines do not always work and you can have a bad reaction to them such as fever or seizures
• Viruses reproduce using the body cells so it is very difficultt to kill them without killing the body cell.
• Viruses are not cells, they are 1/100 the size of a bacterium and live inside your cells, duplicating my using the cell's machinery until the cell bursts releasing the viruses.
• bacteria make you feel ill by producing toxins that damage your cells
• protists are single-celled eukaryotes, some are parasites.
• Some fungi are single-celled, and others have a body made up of hyphae that can grow and penetrate human skin and the surface of plants. These hyphae can produce spores.
• be hygienic, destroy vectors, isolate infected individuals and vaccinate