Transmission Routes Determine Prevention
Definition
Transmission
The passing of a pathogen from an infected organism to another organism.
- Transmission is the passing of a pathogen from an infected organism to another organism.
- Prevention works by breaking the route used by the pathogen.
Key Idea
Match the control method to the transmission route in every explanation.
Water and Airborne Transmission
- Cholera bacteria spread in water contaminated with faeces from an infected person.
- Clean drinking water, sewage treatment, handwashing and safe food preparation reduce cholera transmission.
- Tuberculosis bacteria spread in droplets released when an infected person coughs or sneezes.
- Good ventilation, covering coughs, testing, isolation and completing antibiotic treatment reduce tuberculosis spread.
- Ash dieback fungal spores travel through the air and on infected plants.
- Removing infected material and restricting movement of ash plants reduce the number of spores reaching healthy trees.
- Sewage treatment separates human waste from drinking water, breaking the faecal-oral route used by cholera bacteria.
- Ventilation dilutes airborne droplets, while isolation reduces the number of susceptible people exposed to tuberculosis.
- Removing infected ash trees reduces spore production, and restrictions on plant movement prevent infected material reaching new areas.
Example
treating sewage prevents cholera bacteria in faeces from reaching drinking water, so fewer people swallow the pathogen.
Vectors and Direct Contact
Definition
Vector
A living organism that carries a pathogen from one host to another without catching the disease itself, for example a mosquito carrying the malarial protist.
- Malaria spreads when a mosquito vector transfers the protist between human bloodstreams.
- Insecticide-treated bed nets, repellents, indoor insecticides and removing standing water reduce mosquito bites or breeding.
- Helicobacter bacteria can spread by oral transmission through saliva or food and water contaminated with faeces.
- Handwashing, safe water and hygienic food preparation reduce oral transmission.
- Mosquito control works at different stages: removing standing water reduces breeding, insecticide kills vectors and bed nets prevent bites.
Body Fluids Spread Ebola
- Ebola virus spreads through direct contact with infected blood or other body fluids and contaminated objects.
- Isolation, protective clothing, disinfection, safe handling of bodies and contact tracing reduce exposure to infected fluids.
- Contact tracing identifies people exposed to Ebola before they unknowingly pass infected fluids to others.
Common Mistake
Do not describe Ebola as airborne because its main route is direct contact with infected body fluids.
Population Controls Add Protection
Definition
Vaccination
Introducing a harmless form of a pathogen into the body so the immune system produces antibodies and memory cells, giving protection against future infection.
- Vaccination reduces the number of susceptible hosts when a suitable vaccine is available.
- Rapid diagnosis and treatment can shorten the time an infected person passes on a pathogen.
Exam technique
- State the route, name the control and explain how the control interrupts that route.
- A list of precautions without a transmission link is weaker than one clear causal explanation.
Evaluate a Control Method
- A control may be effective but limited by cost, access, public compliance or the pathogen's ability to spread before symptoms appear.
- Using several controls together usually blocks more than one stage of transmission.
- A prevention programme is stronger when it combines controls because no single measure is completely effective.
Self review
- How does cholera spread and how can its spread be reduced?
- Give two controls for airborne tuberculosis.
- How do bed nets reduce malaria transmission?
- Why is protective clothing used when treating Ebola?
