Animal activists are calling for the US government to stop the importation of non-human primates for laboratory use after documents from the American Centers for Disease Control and Prevention (CDC) reveal that deadly pathogenic agents, zoonotic bacteria and viruses – including one deemed to be a bioterrorism risk – entered the country with monkeys imported from Asia between 2018 and 2021.
Documents obtained by People for the Ethical Treatment of Animals (Peta) and seen exclusively by the Guardian, along with a case report by the American Association for Laboratory Animal Science, reveal that there have been six cases of Burkholderia pseudomallei identified in primates imported from Cambodia to the US.
The CDC did not immediately respond to a request for comment. Peta has written to the CDC urging that they immediately stop the importation of all non-human primates for the protection of US residents, for the integrity of science, and for the welfare of the animals and their ecosystems.
B pseudomallei, endemic in south-east Asia, causes melioidosis, a rare but potentially deadly disease in humans, usually caused by contact with the pathogen in soil or water. It has a mortality rate of up to 50% and B pseudomallei is, according to the CDC, a “Tier 1 select agent” with potential as a bioterrorism agent.
Dr Lisa Jones-Engel, a Peta senior science adviser, told the Guardian: “There is no indication that the CDC or research industries have been transparent with the public about these diseased monkeys.”
Published last week, the case report titled “Melioidosis in a Cynomolgus Macaque Imported to the United States from Cambodia” reveals that one of the macaques entered the US from Cambodia by air with 359 other macaques and was diagnosed with B pseudomallei in quarantine in Texas in January 2021. Imported non-human primates, or NHPs, are held in CDC-mandated quarantine for 31 days while undergoing testing for infectious diseases.
The macaque was euthanized due to concerns about zoonotic transmission and potential introduction of this Tier 1 select agent into the environment. The report reveals that the other 359 monkeys shipped with the infected monkey “appeared healthy at the end of the quarantine period and were released from CDC-mandated quarantine”.
However, asymptomatic infected animals can shed B pseudomallei into the environment. Jones-Engel said: “Monkeys imported from Asia can harbor the Burkholderia pathogen for months, shedding the bacteria via their feces, urine, blood and saliva into the environment. The CDC knows the danger to humans and has failed to warn the public.”
The report confirms that the importation of animals infected by B pseudomallei could introduce the organism into the US, stating: “Vigilance is critical to preventing its introduction via imported animals.” At present, melioidosis is not a notifiable disease, though the report authors recommended this be considered.
The report identified five other macaques from Cambodia in separate shipments that were diagnosed with B pseudomallei, one during quarantine, and four others several months after they had been released from quarantine.
Direct transmission of the disease from animals to humans is rare but can occur. There are about 12 human cases a year in the US, mostly in travelers to Asia or northern Australia.
However, on 27 July 2022, the same day Peta obtained a response to a Freedom of Information Act request, the CDC issued a warning about the presence of B pseudomallei in the environment in the Mississippi Delta. This is the first time it has been detected in the soil and water in the US and came after two people in the state of Mississippi were diagnosed with melioidosis, one in 2020 and the other in 2022. Neither had traveled, and both were hospitalized but recovered.
The papers the CDC released in July also reveal that since 2019 the increase in imported primates has been accompanied by an increase in monkeys arriving with other zoonotic pathogens, including tuberculosis, Yersinia pseudotuberculosis, Y entercolitica, campylobacter, malaria, as well as hemorrhagic gastroenteritis, “consistent with filovirus infection”. Filoviruses include Ebola and Marburg viruses. Both are Tier 1 select agents.
Primates who were dead on arrival increased from two in 2017 to 11 in 2021, and monkeys dying in quarantine increased from 29 to 125. Primates who were ill but recovered and released rose by 2,280% from five to 119 in 2021, and overall mortality increased from 31 to 136 over five years.
A veterinary adviser for Action for Primates, Dr Nedim Buyukmihci, told the Guardian: “Non-human primates in a free-living situation are unlikely to spread disease to people. But, when they are trapped, transported or confined, they become highly distressed and can shed disease-causing organisms. This data emphasize the potentially significant public health risk of transporting and using non-human primates in laboratories.”
Long-tailed macaques, natives of south-east Asia, are the most heavily traded primate for use in laboratories and are now endangered in part due to the exploitation by the research industry.
Historically, China exported the majority of macaques to the US but ceased trading during the coronavirus pandemic. This, combined with increased demand from the research industry, has resulted in a rise in wild and farmed monkey exports from Cambodia, Mauritius, Vietnam and resumption in trade from Indonesia, Laos and the Philippines. Trappers in Indonesia were filmed inflicting violence on wild macaques during their capture.
In recent years, the number of macaques exported from Cambodia to the USA has more than tripled from 5,851 in 2018 to 18,870 in 2021. The US is the largest importer of primates in the world and the only country to have legally imported wild macaques since 2014.
Jones-Engel said: “The increase of diseases in the NHP is potentially a result of the increase in wild-caught monkeys being inserted into the monkey farms and/or exported.”
Long-tailed macaques are often used in toxicity testing to identify adverse effects of drugs or chemicals. The restrained monkeys are dosed by injection, infusion or a tube forced into their stomach without anesthetic. Dosing can last for months or years with side-effects including pain, shaking, vomiting, internal bleeding and death.
Proponents say there would be no production of medicines without animal research. However, the US Food and Drug Administration reports that animal tests have a 92% failure rate predicting the safety or effectiveness of pharmaceuticals in humans.
Cambodia has eight monkey farms. However, the industry has come under scrutiny when in November this year, federal prosecutors charged eight members of a primate smuggling ring for their role in laundering 3,000 endangered wild macaques from Cambodia to US commercial exporters. The US justice department’s indictment charges two Cambodian government wildlife officials, and the owner and staffers from Vanny Bio Resources, a macaque supplier in Cambodia. The indictment includes two unnamed co-conspirators in the US in Alice, Texas, and Miami.
The CDC has previously said Cambodia suspended its export of primates to the US.
“Primate experimentation in the US is part of the global wildlife trade in endangered species,” Jones-Engel said. “It’s unspeakably cruel and a substantive threat to public health. It must end,” said Dr Jones-Engel.
