Spread and control of diseases

Many factors can contribute to the spread of diseases. The route of disease transmission is of primary importance, as it will influence the spread of a disease and determine the appropriate mechanism of disease control.

Routes of disease transmission include:

  • Aerosolised transmission: inhalation of pathogen-containing droplets exhaled by an infected individual.
  • Vector transmission: pathogens spread by organisms, such as insects, from one host to another.
  • Direct contact: exposure to infected bodily fluids or surfaces.
  • Ingestion: consumption of contaminated food or water.

For epidemiologists to manage infectious diseases, they need to understand the factors that influence the spread of the disease. These include:

Host factors

  • Cultural practices, e.g. handshaking, hugging or kissing in greeting.
  • Immunity (or lack of) to the pathogen within a population .
  • Population density
  • Healthcare access and economic conditions

Vector factors

  • Disease reservoirs, referring to the presence of animal populations infected with the pathogen. For example, there are Ebola outbreaks most years as it is endemic in bat populations.
  • Vector population size and extent. For example, high numbers of Anopheles mosquitoes that transmit malaria contribute to its spread.

Environmental factors

  • Physical e.g. lack of ventilation increasing the spread of airborne diseases
  • Climate e.g. malaria-bearing mosquitoes thrive in tropical locations, but cannot survive in cold conditions
  • Access to clean water and sanitation

The control of a pathogen is also best understood in two ways:

Scientific control
The use of technology, improved infrastructure and goods or services to limit the spread of the pathogen. This may include using medications, water treatments, face-masks and vaccinations.

Social control 
The manipulation of human behaviour to reduce the spread of the pathogen, including education campaigns on washing hands, or employing contact-tracing and quarantines.

Explore these factors in greater detail by clicking on the hotspots below to view the case studies.

Check your understanding by selecting the correct responses in the following multiple choice and true or false questions on the spread and control of disease.