How do infections like the coronavirus jump from animals to people?

Zoonotic diseases, which pass from animals to humans, kill millions of people every year. Where do they come from and how can we avoid them?

A deer tick climbs a blade of tall grass in the woods. It stretches its front legs as far as it can, waiting for a passerby. When a hiker brushes past, the tick clings on. It finds a prime position, cuts into the skin, and inserts its feeding tube. If the tick carries the bacteria that causes Lyme disease, that virulent microbe passes into the tick’s human host, and the person now has a zoonotic disease.

Also called zoonoses, zoonotic diseases are the many kinds of illnesses that pass from animals to humans. Almost 16 percent of all deaths worldwide can be attributed to infectious diseases, and zoonoses account for 60 percent of known infectious diseases and 75 percent of

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