Emerging Infections - Further Information

Emerging infections have been appearing at an average rate of one per year.

• See here for a Timeline Diagram of emerging infections since 1980 (PDF, 229 KB) 

The pattern of human infectious disease across the globe changes all the time. The reasons are complex, but basically result from an interaction between the infectious agents themselves and human activities. These include:

Microbial adaptation and change

Microbes continually have to adapt to the environment they live in. The changes that result may allow them to evade the human immune system, or provide them with a new ability to invade human cells. They can also develop resistance to drug treatments and some changes may make vaccines less effective.

Susceptibility to infection

Our bodies have many defences against infection – these may be physical, cellular and chemical. But they can become less efficient through disease, hereditary factors or other factors, for example malnutrition, making us more vulnerable to infection.

Climate, weather and the environment

Infectious diseases may be affected by short-term weather conditions (such as drought or flood) or appear at particular times of the year (such as influenza in the winter and some types of gastro-enteritis in summer). Climate can have a direct impact on how diseases are spread; either through effects on micro-organisms and the agents (vectors), which are often insects such as ticks and mosquitoes, that can carry and transmit disease, or because we change our behaviour in response to climate change. Changes to the environment mostly affect diseases that are spread by water, air, food, or by vectors.

Economic development and land use

Economic development can have an effect on the environment, resulting in changes that affect how micro-organisms reproduce and are transmitted. Changes in the way we use land, including agricultural practices, deforestation and reforestation, dam building and irrigation can mean that we are more likely to come into contact with animals, vectors and other sources of infection.

Human demographics and behaviour

Unsafe sex, drug abuse and outdoor recreation may result in increased exposure to an infectious agent and, in areas that become more heavily populated, there may be a greater chance of catching a disease. Other important changes in the way people live now include the movement from countryside to towns, the growth of towns themselves, populations getting older and the increase in chronic diseases.

Technology and industry

Some diseases emerge as a direct consequence of technological change. New medical treatments and procedures like blood transfusion and organ transplantation, have created new ways for micro-organisms to spread and infect people. Changes in food processing and packaging, animal farming and the fact that we now get our food supplies from all over the world also provide the potential for new diseases to emerge.

International travel and commerce

The speed and ease with which we – as well as animals, food and other goods - can be transported around the world, and the arrival of the “global market” have made it much easier to spread both infectious agents and the vectors or vehicles that can transmit them.

Breakdown in public health

Existing infections and the emergence of new ones in many areas of the world can be caused by dirty conditions, poor hygiene and a lack of drinkable water. In other places, a breakdown of public health initiatives, such as spraying mosquitoes (vector control) or preventative immunisation programmes has meant that diseases that were previously controlled are re-emerging.

Other factors

Also contributory to the re-emergence of disease are poverty and social inequality, urban decay, war and conflict; lack of political will and intentional biological attacks.

Three-quarters of emerging infections are caused by micro-organisms spread from animals (zoonoses) and are linked to people with who have contact with pets, farm animals or wildlife.

Last reviewed: 11 August 2011