Image copyright Keith Nelson Image caption The research programme is investigating whether monkeys can be useful in researching animals
Scientists at the National Zoo in Washington DC were forced to re-engineer their plane as dead and infirm macaques were left to die on board.
Earlier this month, six primates from a Vietnamese-American sanctuary were flown to the zoo for a study that could boost US anti-malaria research.
But just three of the macaques were able to fly without ill health, and died on arrival.
An investigation has been launched to find out why some monkeys needed to be removed.
Consequences of bad flying
The six macaques arrived in the US from Ho Chi Minh City on a Cessna plane with no fresh clothes, and only six days’ leave under the terms of the trip.
Without a fresh supply of food, those macaques that could fly were placed on a transport crate for a cross-country flight to Washington.
But by the time the crate landed in Dulles airport, only three of the six macaques were moving. All five died shortly after being loaded onto the aircraft.
Image copyright Keith Nelson Image caption The deaths of the macaques left crew and scientists at the National Zoo with a major dilemma
The episode led to the flight being re-engineered with fresh food and its cargo compartment opened, according to staff. The other macaques spent the next two days in quarantine, and eventually returned to the sanctuary in their normal condition.
The macaques had been taken from the Wildlife Conservation Society’s Wildlife Conservation Hospital in New York City.
The university investigators are reviewing procedures for future flights to assess the needs of scientists involved in such projects.
An official at the Wildlife Conservation Society told the US Smithsonian website it was reviewing the incident.
No place for experiments on monkeys
“Although patients receive beds for adequate rest and, occasionally, water, the cage does not allow for light or ventilation, which can be responsible for abnormalities of health,” the zoo’s research programmes division said in a statement.
In the last decade, researchers have been brought in from as far afield as Mongolia, Kenya and Vietnam to develop new therapies against malaria, for example.
However, this does not mean that the US government cannot test a drug on primates.
David Townsend, a conservation specialist at the National Zoo, said macaques were essential part of the scientific experiment.
“The macaques performed a hands-on, free-ranging encounter with the vaccine and showed the use of the antibody had the same long-term effect on the human as the antibody had on the macaques,” he told the Smithsonian.
“This pathway demonstrates the potential of the new technology.”
Some studies, such as vaccines, even rely on the macaques to reactivate the gene needed to produce a therapy.
However, experts warn that there is a stark difference between a macaque being used for purposes not intended for them, such as playing in a game, and the macaques being used for research.
“There is a real problem in the logistics of transporting these macaques without discomfort to study their health and behaviour,” said David Parish, director of advocacy and campaigns at the World Society for the Protection of Animals.
“Monkeys in laboratories are often used as a ‘testing bench’ for new technology. Without adequate protection for primates in travel and disposal, the trip to laboratory is a potential death sentence,” he added.
Image copyright BBC image caption Research on monkeys in laboratories is something that has been criticised by wildlife group PETA
“If it is discovered that flights with macaques are taking place on airlines that regularly fly endangered species or dangerous substances, then these airlines must take action to immediately cease transport.”
Activists from PETA (People for the Ethical Treatment of Animals) claim that the flight back to the sanctuary was caused by one of the plane’s engine’s mufflers being badly damaged.
PETA also criticised one of the flight crew for drinking alcohol on the plane, and claim that crew are kept unsupervised and untrained when handling the macaques.
The Wildlife Conservation Society issued a statement on Friday saying it had disciplined two of its staff and was investigating why the macaques died.
“Our primary concern is the welfare of the macaques and all that we do at the Atlanta and Washington, DC, zoos and conservation centre,” it said.