Infection and immunity
Infection and immunity

This free course is available to start right now. Review the full course description and key learning outcomes and create an account and enrol if you want a free statement of participation.

Free course

Infection and immunity

1.1  What are infectious diseases?

Infectious diseases are distinguished from other illnesses and disorders because they can be transmitted from someone who is ill either directly or indirectly to other individuals, who then develop the same infectious disease and are also able to pass it on. A familiar example is the ‘common cold’ which almost everyone has experienced at some time in their lives (Figure 1). Non-human animals and plants also suffer from infectious diseases, which cause massive losses to food crops and livestock, but our focus in this course is on infection in humans.

Figure 1  The common cold affects children and adults all over the world: (a) Vietnam. (b) United Kingdom.

By contrast, health problems that cannot be transmitted between individuals, such as heart disease, diabetes, lung cancer, arthritis and depression, are known as non-communicable diseases (or NCDs). However, a few NCDs also have an infectious component, for example:

  • in most cases of cervical cancer there is evidence of infection with a specific virus (the human papilloma virus, or HPV)
  • hepatitis viruses cause liver disease and cancer of the liver
  • a bacterium (Helicobacter pylori) causes stomach ulcers.

These examples illustrate the point that there is some overlap between some infectious and non-communicable diseases. The biology of bacteria and viruses is the subject of Session 3 Pathogens and infectious diseases.

For completeness, we should mention here that the third major category of diseases, disorders and disabilities is termed injuries, i.e. physical damage to the body caused by accidents or violence.


Take your learning further

Making the decision to study can be a big step, which is why you'll want a trusted University. The Open University has 50 years’ experience delivering flexible learning and 170,000 students are studying with us right now. Take a look at all Open University courses.

If you are new to university level study, find out more about the types of qualifications we offer, including our entry level Access courses and Certificates.

Not ready for University study then browse over 900 free courses on OpenLearn and sign up to our newsletter to hear about new free courses as they are released.

Every year, thousands of students decide to study with The Open University. With over 120 qualifications, we’ve got the right course for you.

Request an Open University prospectus