WJEC Biology for A2: Student Bk

Key Terms Toxin : A small molecule, e.g. a peptide made in cells or organisms, that causes disease following contact or absorption. Toxins often affect macromolecules, e.g. enzymes, cell surface receptors. Faulty CFTR channel proteins are associated with cystic fibrosis, as described on p254. Link ▪ A toxin is produced by V. cholerae in the small intestine that affects the chloride channel proteins, called CFTR. Water and many ions, including Cl – , Na + , K + and HCO 3 − are not absorbed into the blood and the patient has severe, watery diarrhoea. This causes dehydration so the blood pressure falls dramatically and the patient may die within hours. ▪ Cholera can be prevented with good hygiene and sanitation. Better sewage treatment, water purification, safe food handling and regular hand washing have all reduced the incidence of cholera. A vaccine is available, providing temporary protection but it is only given to people at very high risk. ▪ Treatment has two strands: – Water and ions are replaced by giving patients electrolytes, either orally or, in severe cases, intravenously. – The bacteria are treated with antibiotics. There is a famous example of epidemiology, i.e. the study of the spread of disease, which dates back to 1854. At the time, it was thought that cholera was caused by ‘bad air’. John Snow, a physician, suspected that it was transmitted by water so he mapped the cases during a cholera outbreak in Soho, London. He identified the water from a pump in Broad (now Broadwick) Street as the source. When its handle was removed, the number of new cases dropped immediately, supporting his hypothesis. Tuberculosis (TB) ▪ Tuberculosis is caused by the bacillus bacterium Mycobacterium tuberculosis. It is named for the tubercles, or nodules of dead and damaged cells in the lungs of people who are infected. Tubercles may contain gas- filled cavities, which are easily seen in X-rays. ▪ The infection spreads rapidly by aerosol transmission, i.e. the inhalation of bacteria- laden droplets from the coughs and sneezes of infected people. This is why in many countries you see signs saying ‘No spitting’. TB spreads very rapidly in crowded conditions; in densely populated cities, it is once again a public health concern. The decreased efficiency of immune systems of HIV-AIDS patients is partly correlated with the recent increase in TB cases in some areas. ▪ The bacteria mainly infect the lungs so patients develop chest pain and they cough up phlegm (sputum), which often contains blood. The bacteria may infect lymph nodes in the neck, which swell. People lose their appetite and develop a fever. ▪ TB is treated with a long course of antibiotics but M. tuberculosis does show some antibiotic resistance. ▪ To prevent TB, the BCG vaccine is given to babies and, if a skin test proves negative, to people up to the age of 16. It provides about 75% protection, but only for 15 years. It is less effective in adults, and only given to those at risk. The vaccine is made from an attenuated (weakened) strain of a related bacterium, M. bovis . BCG stands for ‘bacillus of Calmette and Guérin’, the French scientists who developed it. Section through Mycobacterium tuberculosis Lung X-ray showing cavities often seen with TB Going further A person who has been exposed to TB may carry anti-TB antibodies, which are detected by a skin test. A negative skin test means they have no antibodies, so they are offered the vaccine. WJEC A2 Biology: Chapter 14 262