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IN THIS CHAPTER

Studying the make-up and reproduction of a virus

Looking at common viruses around the world

You’ve probably said, “I caught a virus” dozens of times in your life. And no wonder — so far humans have identified close to 7,000 virus species. We know there are hundreds of thousands more and think there are millions, if not trillions, more. Some viruses infect people; others infect other animals; and still others infect plants, fungi, or even bacteria. (There are even virophages that infect viruses themselves.) Viruses — infective agents that can only reproduce inside another cell — are pretty simple, but what they cause is not so simple. They may cause no symptoms. They may wreak havoc on us. They may cause something in between or go back and forth.

Virus particles (virions) are very small — smaller than we can see with a regular microscope. Yet they still manage to perplex us. Sometimes it even seems like they outwit us. As with any enemy, getting to know what a virus is and how it works is instrumental to thwarting it, and this chapter can help. As you also find out here, some viruses can be prevented by vaccines, while others still evade science’s attempts to prevent them.

There are more viruses than we know out there. As people increase transportation, move into areas with few inhabitants, and have contact with different animals, the world becomes increasingly connected. What may have caused an unknown outbreak in an isolated location that is quickly extinguished can become a large epidemic.