Infection and immunity
Infection and immunity

Start this free course now. Just create an account and sign in. Enrol and complete the course for a free statement of participation or digital badge if available.

Free course

Infection and immunity

3.4  Introducing parasites and protists

The term parasite refers to an organism that lives in or on the body of another organism (its host) and benefits at the host’s expense, so strictly speaking all pathogens are ‘parasites’. However, in discussions of human infectious diseases, the term is restricted to:

  • multicellular parasitic worms
  • pathogenic protists: single-celled organisms with similar cells to those of animals (multicellular protists exist, but none are human pathogens).

In 2013, the World Health Assembly identified 17 so-called ‘Neglected Tropical Diseases’ affecting over one billion people; it is notable that eight are caused by parasites and three by protists. Figure 2 shows sites on the surface or inside the human body that parasites and protists can infect. Click or tap on each of the labels in Figure 2 to reveal a brief description in a box below the diagram of the disease states the pathogen causes and the site(s) it occupies in the body.

Active content not displayed. This content requires JavaScript to be enabled.
Figure 2  Some parasites and pathogenic protists, the diseases they cause, and and the sites they infect in the human body.
Interactive feature not available in single page view (see it in standard view).

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, we offer two introductory routes to our qualifications. You could either choose to start with an Access module, or a module which allows you to count your previous learning towards an Open University qualification. Read our guide on Where to take your learning next for more information.

Not ready for formal University study? Then browse over 1000 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 prospectus371