Unit 3 · Infection & Response
Communicable Diseases & Pathogens
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Pathogens
- Pathogens are microorganisms that cause infectious (communicable) disease. They may be viruses, bacteria, protists or fungi, and they infect plants as well as animals
- Spread by direct contact (touching, sexual contact, body fluids), by water (drinking or washing in contaminated water), or by air (droplets from coughs and sneezes)
- Bacteria reproduce rapidly inside the body and may produce toxins (poisons) that damage tissues and make us feel ill
- Viruses live and reproduce inside cells, causing cell damage when they burst out
The diseases you need
| Disease | Pathogen | Symptoms and effects | Spread by | Control |
|---|---|---|---|---|
| Measles | virus | fever, red skin rash; can be fatal with complications | inhaling droplets from sneezes and coughs | vaccination of young children |
| HIV | virus | flu-like illness at first; then attacks immune cells; late stage is AIDS, when the immune system can no longer deal with other infections or cancers | sexual contact; exchange of body fluids such as blood when drug users share needles | antiretroviral drugs; condoms; not sharing needles; screening blood |
| Tobacco mosaic virus (TMV) | virus | mosaic pattern of discolouration on leaves; growth reduced because photosynthesis is reduced | contact between plants | remove infected plants; wash hands and tools |
| Salmonella | bacterium | fever, abdominal cramps, vomiting and diarrhoea, caused by the bacteria and the toxins they secrete | ingested in food, or on food prepared in unhygienic conditions | poultry vaccinated in the UK; cook food thoroughly; hygiene |
| Gonorrhoea | bacterium | thick yellow or green discharge; pain on urinating | sexual contact | antibiotics (many strains now resistant to penicillin); barrier contraception such as condoms |
| Rose black spot | fungus | purple or black spots on leaves, which turn yellow and drop early; less photosynthesis so less growth | water or wind | fungicides; remove and destroy affected leaves |
| Malaria | protist | recurrent episodes of fever; can be fatal | the mosquito, a vector, in its bite | stop mosquitoes breeding (drain standing water); mosquito nets; insecticides |
Reducing the spread of disease
- Hygiene: hand washing, cooking food properly, disinfecting surfaces, using tissues
- Isolating infected individuals so they cannot pass the pathogen on
- Destroying or controlling vectors, for example mosquitoes
- Vaccination, so people do not catch the pathogen and pass it on
- Barrier methods of contraception for sexually transmitted infections; not sharing needles