Does this organism look like a space alien? A scary creature from a nightmare? In fact, it’s a 1-cm long worm that lives in the human body and causes serious harm. It enters the body through a hair follicle of the skin when it’s in a much smaller stage of its life cycle.
Like this worm, many other organisms can make us sick if they manage to enter our body. Fortunately for us, our immune system is able to keep out most such invaders. When you read this chapter, you’ll learn how your immune system keeps you safe from harm—including from scary creatures like this!