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Public health and development: Infrastructure, social norms, and health behaviours

3 Pathways to infectious diseases

This section follows the definitions used by the US Centers for Disease Control and Prevention.

Germs are part of our daily life. While most germs are innocuous, there are some that transmit infections (for example, several types of virus cause the common cold). An infection occurs when germs enter the body, increase in number, and the body reacts. Infectious diseases are the main cause of death in low-income countries, and most infectious diseases can be cured with existing technology such as antibiotics or vaccines.

Germs depend on people, the environment, and/or medical equipment to move from the source (where the germs live) to a susceptible agent (a person or animal that is not immune to that germ and can be infected by it). The way germs move to the susceptible agent is called transmission. The route of transmission is called a pathway. For example, the COVID-19 virus was transmitted (spread) from person to person through the air.

Faecal–oral contamination is one of the major causes of diseases that lead to preventable deaths in low-income countries. Figure 9 shows how faeces in the environment makes its way to food and drinking water (and, in turn, affects a susceptible agent’s health status) through (1) contaminated groundwater, due to shallow wells and the lack of sanitation; (2) hands, due to poor handwashing practices; (3) flies, and fields that are irrigated with contaminated water or with a high presence of animal or human faeces. Diarrhoeal diseases are transmitted in such ways.

This diagram illustrates the faecal–oral transmission pathways affecting human health. It begins with faeces, which can contaminate fingers, fields and flies, and ground or surface water. These contaminated intermediaries in turn affect food and drinking water (which also affects food), both of which directly influence health status. There are multiple feedback loops, including faeces re-entering the environment through contaminated fingers and fields, reinforcing the cycle. The diagram highlights how poor sanitation and hygiene can lead to the ingestion of faecal pathogens and thus deteriorate health.
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https://books.core-econ.org/insights/public-health-and-development/03-pathways-to-infectious-diseases.html#figure-9

Figure 9 Transmission routes (‘pathways’) of faecal–oral contamination. Arrows represent transmission routes for pathogens.

Hugh Waddington and Birte Snilstveit. 2009. ‘Effectiveness and Sustainability of Water, Sanitation, and Hygiene Interventions in Combating Diarrhoea’. Journal of Development Effectiveness 1(3): pp. 295–335.

Figure 10 shows how clean water, sanitation, and good hygiene can minimize the transmission of diseases. Safe sanitation will ensure less contamination of ground or surface water and fields. Proper handwashing with water and soap will also stop transmission. Water treatment, either at the source or at the point of use, will also reduce the pathways to transmission.

This diagram shows the faecal–oral transmission pathways with potential points of intervention to improve health outcomes. Just as in Figure 9, starting from faeces, transmission routes include fingers, fields, and flies, and ground or surface water, which contaminate food and drinking water, ultimately affecting health status. Intervention strategies are marked in red. Sanitation blocks faecal contamination of fingers and fields, hygiene interrupts transmission via hands and food handling, source treatment ensures clean water, and point of use (POU) treatments protect drinking water and food at the household level. These interventions aim to reduce exposure to pathogens and improve health.
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https://books.core-econ.org/insights/public-health-and-development/03-pathways-to-infectious-diseases.html#figure-10

Figure 10 Barriers to disease transmission arising from hygiene, sanitation, and water treatment at source or point of use (POU).

Hugh Waddington and Birte Snilstveit. 2009. ‘Effectiveness and Sustainability of Water, Sanitation, and Hygiene Interventions in Combating Diarrhoea’. Journal of Development Effectiveness 1(3): pp. 295–335.

By the mid-twentieth century, the poliovirus could be found all over the world, and it killed or paralysed over half a million people every year. With no cure, and epidemics on the rise, there was an urgent need for a vaccine.

Similar flowcharts can be used to analyse the spread of other diseases that can be prevented with vaccines. For example, the poliovirus is transmitted person-to-person, spreading mainly through the faecal–oral route or, less frequently, by a common vehicle (for example, contaminated water or food). The main barrier to transmission is the polio vaccine. Thanks to massive polio vaccine campaigns, the disease has been almost eradicated worldwide, though there are some countries, such as Afghanistan and Pakistan, where it is still endemic.

Exercise 2 Pathways to disease transmission

Select one infectious disease from this list: influenza, tuberculosis, ringworm, hookworm. For this disease, draw a flowchart diagram like Figure 10 to show:

  • the source(s) of this disease
  • ways that this disease can be transmitted to susceptible agents
  • how the pathways to transmission can be reduced.

You may find it helpful to do some research on your chosen disease (and the available treatments).