PORTLAND, Oregon (AP) — As an exotic pet trade boomed over the past few decades and Americans bought cute tiger cubs and baby monkeys, sanctuaries sprang up across the nation to take care of the animals that were abandoned when they reached adult-size or were no longer wanted.

The growth in both the number of the pets and the sanctuaries that rescued them has led to attacks.

Since 1990, more than 20 people have been killed by captive big wild cats at sanctuaries, zoos and private residences, more than 200 people have been mauled and 200-plus wild cats have escaped, according to one of the nation's largest wild cat sanctuaries.

The latest death is head keeper Renee Radziwon-Chapman, 36, who was killed by a cougar at an Oregon sanctuary last week.

Experts say that because sanctuaries are largely unregulated and anyone can open one, there are no uniform safety protocols. And over-confidence or human error can lead to tragic consequences even among the most experienced of caretakers.

"People running legitimate sanctuaries provide an alternative" to putting a wild cat down when it is no longer wanted by its owner, said Vernon Weir, director of the Nevada-based American Sanctuary Association which certifies sanctuaries.

"But it's a risky business when you're dealing with dangerous wild animals. You can't leave any room for error," Weir said.

For decades, exotic animals have been imported into the U.S. and openly bred for the pet trade. Despite new laws that limit the trade in some states, people can easily buy an African rodent, a chimpanzee, or a baby leopard at a flea market or over the Internet.

Experts estimate the U.S. exotic pet trade is a multibillion-dollar industry. Hundreds of sanctuaries have opened throughout the U.S.

About 80 sanctuaries currently house big cats, the International Fund for Animal Welfare says. Only a dozen of them are certified or verified by two certifying organizations, the American Sanctuary Association and the Global Federation of Animal Sanctuaries.

There's little governmental oversight and no one sets rules for how sanctuaries operate.

As a result, safety procedures meant to protect staff and animals vary. Most sanctuaries develop their protocols. The certifying associations require safety standards, but in most cases don't define specific rules.

WildCat Haven sanctuary where the head keeper was killed on Nov. 9, was "verified" by the Global Federation of Animal Sanctuaries. Verification means the sanctuary satisfied 60 different standards, including safety.

The organization recommends "redundancy" when it comes to safety, its executive director Patty Finch said, meaning two lockout doors or two staff members present. "It won't eliminate the risk factor, but can certainly reduce it," Finch said.

Still, she said, risk is inherent in the job. "You can have the best protocols in the world and something can still go wrong."

WildCat Haven has good safety rules in place, Finch said.

Its safety manual specifies that a staff member can enter the main enclosure to clean or make repairs only after the animals are locked away in a smaller cage. Two people must be present when animals are locked up. And a caretaker can't be alone with an animal in the same space.

Sanctuary officials said Radziwon-Chapman apparently broke those rules: she worked alone, locked only one of three cougars in the smaller cage, and went into the main enclosure with the other two cougars.

The woman's family said they don't believe the wife and new mother broke any rules, and she had expressed concerns about working alone just days before the attack.

The best way to stop the attacks, experts say, is to reduce the need for sanctuaries by the curtailing the exotic pet trade.