These larger invaders are sometimes more difficult to kill than the smaller ones.
Malaria and sleeping sickness are two diseases caused by protists.Protists are soft, jellylike creatures that usually need to be surrounded by plenty of water in order to survive.
As our bodies contain lots of water, they can live inside us.
Not all protists live inside people or other animals.
Some live harmlessly in soil and water.
Protists are not as easily spread from one person to another as some microbes, such as bacteria and viruses. But they have special ways of infecting people. Some harmful protists are spread by biting insects.
These flies spread sleeping sickness, and mosquitoes spread malaria and yellow fever.
When a mosquito bites a person, it sucks up blood.
At the same time, it may infect the person's blood with the protist that causes yellow fever.
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