A Closer Look

So far the picture is broad: you are a host, parasitism is the planet's most common lifestyle, and worms may even steady the immune system. That last idea is the one worth pressing on.

The rest of this lesson zooms in. We will meet the face mites in detail, follow the everyday route that pinworms and Toxoplasma use to spread, and look at the boldest test yet of parasites as medicine — against a disease of the brain itself.