Explain how pathogens are spread and how this spread can be reduced or…

The idea

Pathogens spread by a route that carries the organism from a source to a new host, and control works by breaking that route. Cholera bacteria spread in contaminated water, so clean water supply and sanitation reduce it. Tuberculosis bacteria spread in airborne droplets from coughs and sneezes, so ventilation, covering coughs and treating patients limit it. Chalara ash dieback fungus spreads airborne as spores, so avoiding moving infected wood and planting material limits it. Malaria protists spread by animal vectors, female mosquitoes, so nets and vector control reduce it. Helicobacter bacteria causing stomach ulcers pass by oral transmission, so hygiene and clean food and water help. Ebola virus spreads in body fluids, so protective equipment and safe handling of fluids and the deceased reduce it. For each disease, name the pathogen type, the route and a matching control measure.

What earns the marks

• Cholera is caused by bacteria and spreads through contaminated water; clean water supply, boiling water and sanitation reduce spread.
• Tuberculosis is caused by bacteria and spreads airborne in droplets from coughs and sneezes; ventilation, covering the mouth and treating infected people reduce spread.
• Chalara ash dieback is caused by fungi and spreads airborne as spores; avoiding movement of infected wood or plants and good biosecurity reduce spread.
• Malaria is caused by protists and spreads via animal vectors (mosquitoes); mosquito nets, repellents and controlling the vector reduce spread.
• Helicobacter bacteria cause stomach ulcers and spread by oral transmission; hygiene, clean food and water reduce spread.
• Ebola is caused by a virus and spreads in body fluids; protective clothing and safe handling of body fluids reduce spread.

Common mistakes and how to put them right

• Naming malaria as a virus or bacterium.

  Put it right: It is caused by protists, so the correction is to link malaria to protists and to its mosquito vector.

• Giving a control measure that does not match the route, such as using mosquito nets against cholera.

  Put it right: Match each measure to the named transmission route.

• Treating Chalara ash dieback as spread by water.

  Put it right: It spreads airborne as spores, so the correction is to state the airborne route and biosecurity measures.

Exam tips

• For each disease, state the pathogen type, the route and one control measure in the same answer.
• Use the exact route word given, such as airborne, water, animal vectors, oral transmission or body fluids.
• Check that the control measure directly interrupts the stated route rather than being a general health measure.