Around 10,000 years ago, somewhere in Africa, a microscopic parasite made a huge leap. With a little help from a mosquito, it left its animal host - probably a gorilla - and found its way to a new host: us.

The single-celled organism Euplotes is very common and can often be seen running up and down the filamentous algae in a pond. The legs are modified cilia, called cirri, that move the protozoan over the substrate. Euplotes is flattened...

Microscopic view of Euglenoid protozoa moving around against blue background

This protozoan feeds by using hair-like cilia on the cap of its bell to waft food particles to its central mouth. Each Vorticella has a contractile stalk that is used to jerk it towards its substrate. Phase contrast cinemicrography

This protozoan feeds by using hair-like cilia on the cap of its bell to waft food particles to its central mouth. Each Vorticella has a contractile stalk that is used to jerk it towards its substrate. Phase contrast cinemicrography