Topic 3: Infection and response

• Health is a state of mental and physical well- being
• Diseases, both communicable and non- communicable, are major causes of ill health. Other factors include: diet, stress and life situations may have a profound affect on both physical and mental health.
• Different types of disease may interact
• Defects in the immune system mean that an individual is more likely to suffer from infectious diseases
• Viruses living in cells can be the trigger for cancers
• Immune reactions initially caused by a pathogen can trigger allergies such as skin rashes and asthma
• Severe physical ill health can lead to depression and other mental illnesses
• Pathogens are microorganisms that cause infectious disease.
• Pathogens may be viruses, bacteria, protists and 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 an reproduce inside cells, causing cell damage
• The spread of disease can be prevented by simple hygiene measures, by destroying vectors, by isolation of infected individuals and by vaccination
• Measles is a viral disease showing symptoms of a fever and 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 intially causes a flu like illness. Unless sucessfully controlled with antiretroviral drugs, the virus attacks the body's immune cells. Late stage HIV infection, or AIDS, occur 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 bodily fluids such as blood.
• Tobacco mosaic virus (TMV) is a widespread plant pathogen affecting many species of plant, 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 grenn discharge from the vagina or penis and pain on urinating. Gonorrhoea is spread by sexual contact. The spread can be controlled by treatment with antibiotics or the use of a barier method of contraception such as a condom.
• Rose black spot is a fungall disease where purple or black spots develop on leaves, which often turn yellow and drop early. It affects the growth of the plants as photosynthesis is reduced. It is spread in the environment by water or wind. Rose black spot can be treated 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 inclue the mosquito. Malaria causes recurrent episodes of fever and can be fatal. The spread of malaria is controlled by preventing the vectors, mosquitoes, from breeding and by using mosquito nets to avoid being bitten.
• The human body has several lines of defence against the entry of pathogens. These include the skin (barrier and antimicrobial), the nose, the trachea, thr bronchi and the stomach
• If a pathogen enters the body, the immune system tries to destroy the pathogen
• White blood cells help to defend against pathogens by: phacgocystosis, antibody production and antitoxi 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.
• If a large proportion of the population is immune to a pathogen, the spread of the pathogen is much reduced (herd immunity)
• 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 antibodies
• The use of antibiotics has greatly reduced deaths from infectious bacterial diseases. However, the emergence of strains resistant to antibodies is of great concern.
• Antibiotics cannot kill viral pathogens.
• Painkillers and other medicines are used to treat the symptoms of the 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 aspiring originates from willow
• Penicillin was discovered by Alexander Fleming from the Pencillium 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 trials is done in a laboratory using cells, tissues and live animals