Causing Diseases
Biology: Cambridge International GCSE Supplement, topic 10.1.2
Spreading Disease
Transmissible diseases are caused by organisms called pathogens. These are ways an infectious (transmissible) disease can spread directly (through body fluids such as blood or sexual fluids) or indirectly (through contaminated water, in the air or by a vector):
Water
- Some pathogens contaminate water supplies. Pathogens can infect organisms that drink this contaminated water.
- Cholera is a disease spread in this way.
Sex
- Diseases that are spread through sexual contact (often simply genital to genital contact) are called sexually-transmitted infections (STIs).
- Physical barriers (such as condoms) are very effective at stopping the spread of STIs.
- Chlamydia is a bacterial infection that causes infertility and often has no other symptoms, so easily spreads. Testing and treatment with antibiotics prevents spread.
- HIV can also be passed on through pregnancy, birth and breastfeeding. Testing and treatment with antiretroviral drugs prevents spread.
Air
- Some pathogens are released into the air inside droplets when an organism coughs or sneezes. These droplets can then be inhaled (breathed in) by other organisms.
- Tuberculosis bacteria are spread in this way.
Animals
- Rabies is a protist that is spread by animals.
- Rabies can be spread by dogs.
Body fluids
- Ebola and HIV are both spread through direct contact with someone else's body fluids (such as blood).
Contaminated surfaces
- Norovirus is spread through contact with contaminated surfaces, often leading to illness when someone touches their mouth after touching these surfaces.
Food
- Salmonella is spread through consuming food contaminated with the bacteria, often leading to illness when undercooked poultry or eggs are ingested.
Test yourself on Causing Diseases
Which of these can be spread by contaminated surfaces?