On his recent travels in Europe, Justin Bieber ran into some problems in Germany. He had not obtained proper papers to bring his pet capuchin monkey into the country, so the monkey was put into quarantine.

That made us wonder: Do capuchin monkeys make good pets? We asked Debbie Leahy, manager of captive wildlife protection for the Humane Society of the United States.

Is it OK to have a pet monkey?

No primate species should ever be kept as a pet. They have very special needs. These are highly social animals. They need to be kept with others of their own kind; that's just critical to their psychological well-being.

Yet breeders in the U.S. sell monkeys as pets.

There are numerous problems with the pet monkey trade. For one thing, the breeders will pull newborn monkeys from their moms when the [baby is] just a few days old. So then the animals are bottle-fed and hand-reared by people. They never learn to become a capuchin or a chimp or a macaque; they don't have the opportunity to learn appropriate behavior from their mother and others in their group.

And yet it's legal to breed and sell a monkey as a pet?

It varies by state and by city. Some states may partially ban primates as pets. Oftentimes you see capuchins and other smaller primates exempted from those laws.

Because they're small?

Primarily. People pretty much understand that a chimpanzee could kill you. Look what [a chimp] did to that poor woman in Connecticut. It ripped her face off. Because of their physical strength they are incredibly dangerous.

And capuchins don't make good pets either?

All primate species can become aggressive. A lot of times when the primate reaches sexual maturity, it becomes extremely aggressive, unpredictable—bouncing off the walls in the house, destroying everything. It ends up being confined for the rest of its life in a little cage in the basement, or [the owner] looks to dump it—maybe at a roadside zoo or a pseudo-sanctuary.

What is a pseudo-sanctuary?

A place that claims to be a rescue operation when it's [actually] either keeping animals in substandard conditions or breeding and selling animals, which no legitimate sanctuary would do.

What happens when a pet monkey begins acting aggressively—say, biting people?

A lot of monkey owners go to a vet and say, "Take his teeth out." Sometimes they do a full dental extraction because the animals bite.

Are there other risks to having a pet primate?

What people don't appreciate is that all primate species can carry zoonotic diseases [infectious diseases that can be transmitted from animals to humans].

How many primates are kept as pets in the U.S.?

It's hard to nail down a precise figure; it's not regulated everywhere. But the estimate is around 15,000 in the United States. We know capuchins are popular as pets because we come across lots and lots of news articles about a pet capuchin attacking somebody, or escaping. We know they're popular in the pet trade. Macaques are popular too. That's really concerning, because they carry a very dangerous virus that has about an 80 percent fatality rate in people.

Do you worry that the publicity about Justin Bieber's capuchin will make other people want to have a pet monkey?

People want to emulate celebrities they admire. When somebody like Justin Bieber is irresponsible and goes out and gets a pet monkey, he sets a very bad example.

As an aside, I would say: That's not the only area of his life where he's setting a bad example.

Yeah, he seems to be a little bit out of control.

I've read that some disabled people use capuchins as "helper monkeys."

That's not a legitimate role. It's a scam. Sometimes [the training of] these so-called helper monkeys [involves] physical abuse, including electric shock. Supposedly they can do things on command, like turn light switches on and off or fetch a remote control. But the Americans with Disabilities Act does not recognize primates as service animals; it only recognize dogs. So it's not a legitimate use of a primate.

What might a parent say to a child who still wants a pet monkey like Justin Bieber has?