The National Institutes of Health (NIH) has announced that it will retire the last 50 chimpanzees it had retained for research purposes to Chimp Haven, a federal government funded sanctuary in Keithville, Louisiana.

Earlier, in 2013, NIH had decided to retire most of its 310 chimps, keeping only 50, which would be required in special circumstances like emergency studies during a global health calamity.

However, the agency failed to live up to its promise by returning only six of the 310 chimps since June 2013, providing no schedule as to when the rest of the chimps would be retired.

Furthermore, NIH intentionally infected many chimps with hepatitis and/or HIV for carrying out medical research, causing many to die as well, CNN reported.

"I think this is the natural next step of what has been a very thoughtful five-year process of trying to come to terms with the benefits and risks of trying to perform research with these very special animals," said NIH director Francis Collins on 18 November.

He added that they have reached a point now where in "five years the need for research has essentially shrunk to zero," Nature reported.

Cathy Spraetz, director of Chimp Haven termed the decision to be "fabulous".

Talking about Collins, she said, "He wanted this to be something he could leave his mark on. When he leaves he wants to know that all the chimps have been retired. He wanted that to be part of his legacy," CNN reported.

She revealed that it's not yet known who will pay for the expansion of Chimp Haven. The organisation will launch a capital campaign in early 2016, though the government might also pay some part of it. The first set of chimps might arrive by the end of 2015.

Earlier in June, the US Fish and Wildlife Service granted chimps endangered-species protection that meant that researchers will have to now get permits to perform chimp studies.

NIH's decision comes only weeks after the People for the Ethical Treatment of Animals (PETA) wrote a letter addressed to the public of Washington DC, where they accused Collins of abusing baby monkeys. The organisation revealed Collins' home address and encouraged people to confront him, Ars Technica reported.