How Global Partnerships Are Saving Golden Lion Tamarins From Yellow Fever

By Kara Arundel, a Save the Golden Lion Tamarin board member and career journalist.

Biologist Andréia Martins in the field. Photo Credit - Sally Foster

The golden lion tamarin, a small monkey with silky, light reddish hair and native only to a small Southeast Atlantic Forest area in Brazil, is the first non-human primate species to be vaccinated against yellow fever. The vaccine and vaccination campaign against the potentially fatal disease was the result of an urgent international effort created in just over a year after a third of the wild golden lion tamarin population, which is endangered, had succumbed to the disease.

“When you work with the conservation of a species, you have a plan to move forward and get to the point where you’re going to save the species and moving forward with that plan and then all these things happen that come in and set you back,” said Carlos Ruiz Miranda, an associate professor at Northern Rio de Janeiro State University.

Ruiz Miranda is also chair of the board of Associação Mico-Leão Dourado (AMLD), a Brazilian non-profit who together with its sister organization, U.S.-based Save the Golden Lion Tamarin (SGLT), is working to protect golden lion tamarins.

Now, nearly four years after the discovery of the disease’s threat to the golden lion tamarins, and during the midst of the global COVID-19 pandemic, hundreds of wild monkeys have been successfully vaccinated. Work is ongoing to vaccinate hundreds more. The result of these efforts not only protects the golden lion tamarin population but could also serve as a model to support other vulnerable animal populations, say those leading this endeavor.

The threat

Yellow fever, which is spread by infected mosquitoes, can lead to serious illness in people. It is endemic to Africa and became established in tropical areas of the Americas in the 1600s. In Brazil, the disease is cyclical and had not previously been documented in the wild golden lion tamarins.   

Ruiz Miranda describes the golden lion tamarins as a sentinel species that helps health officials predict risks to the human population. And that’s what started to happen in Brazil in 2016 and 2017 when yellow fever began threatening animals and humans.

It took months to understand the full impact the disease was having on the golden lion tamarin population. 

The monkeys live in the lowland Atlantic coastal forest in 13 isolated blocks of forest. Their habitat is threatened by encroaching development, although some of the land is in protected areas. AMLD’s goal is to have 2,000 golden lion tamarins living in at least 25,000 hectares, or 62,000 acres, of connected and protected forest — a population that scientists believe would persist in the long term and retain a target level of genetic diversity.

The yellow fever concerns began when one golden lion tamarin carcass was brought to AMLD’s lab and found positive with the disease. Eventually, researchers estimated that 32% of the wild golden lion tamarin population, or about 1,200 of 3,700 of the animals in the wild, died due to yellow fever. Two of the blocks of isolated forest lost over 90% of their golden lion tamarin populations, said Ruiz Miranda.

James Dietz, a conservation biologist and founding director of both AMLD and SGLT, said he was an emotional wreck after learning of the animal’s deaths and the ongoing threat to those still alive. 

The golden lion tamarin is a source of pride for Brazilians. Its image is on the country’s currency and stamps. The monkeys are also admired worldwide by animal lovers, including at 159 zoos across the globe with golden lion tamarins in their collections. Those zoos participate in a cooperative breeding program that maintains genetic diversity among the animals. The golden lion tamarins living in zoos serve as insurance should they be needed to help recover the wild population.

“They’re beautiful animals,” said Ruiz Miranda. “You have to keep beautiful animals around and beautiful things. You can’t let them disappear.”

Meta team in the field. Photo credit - Andréia Martins/AMLD

The vaccine

For decades, virologist Marcos da Silva Freire has worked on the development of vaccines for humans. He is currently a scientific advisor at Oswaldo Cruz Foundation, which functions as Brazil’s health institution. Over the years, the foundation has developed human vaccines for dengue fever,  Zika, yellow fever, mumps, rubella and more. The foundation had never worked on vaccines for animals, Freire said.

The yellow fever outbreak that began in late 2016 was a significant event with many human deaths reported in areas that had been considered free of the disease, according to the scientific journal Viruses. 

As the country worked to distribute yellow fever vaccines to humans, Freire and others wondered if that vaccine could also protect the golden lion tamarins. Freire has a personal affection for the animals. His family’s farm was one of the first to welcome reintroduced zoo-born golden lion tamarins in the 1980s and he is an AMLD board member.

But while there was support among those involved in conservation of the species to test the efficacy of the human yellow fever vaccine on the captive golden lion tamarins, there were concerns that those experiments would cause adverse effects in the animals.

Freire and his team diluted the human yellow fever vaccine to be safe for the 1-pound monkeys. The experiments — supported with grants from SGLT and AMLD, vaccine donations from Brazil’s national health institution, and the cooperation of the Oswaldo Cruz Foundation and the Primate Center of Rio de Janeiro — were complex because scientists had to collect blood samples of individual animals at different intervals to test for the virus’s antibodies. The animals’ behaviors were also observed and their temperatures measured. This careful work showed that the vaccine was safe and  highly effective in golden lion tamarins. One shot is believed to provide life-time immunity against the disease as it does in humans.

“Since the beginning, my feeling was that the vaccine would work,” Freire said.

But getting an effective vaccine was only part of the solution. The successful inoculation of golden lion tamarins in the wild would be another hurdle.

The vaccination campaign

To begin vaccinating the wild golden lion tamarins, scientists had to first figure out which government entity would provide the needed permits. Because this was the first time a wild animal population was being inoculated in Brazil, the permits, it was realized, had to come from multiple agencies, including the health, agriculture, and wildlife ministries, Ruiz Miranda said.

Just as the needed permits were acquired and the vaccination campaign began, COVID-19 emerged putting the vaccination campaign in jeopardy by forcing changes to the approach and timing of the campaign, said Dietz.

“I was terrified, both for GLTs and for AMLD personnel,” Dietz said. “At that point [COVID-19] vaccines were not available and we didn’t know if GLTs could get COVID. We lost a beloved partner and friend. Sad and scary times indeed.”

The pandemic interrupted the translocation of vaccinated golden lion tamarins into their native habitats and sending equipment to Brazil internationally was logistically difficult, he said.

The scientists adapted and persevered with the delicate work.

Biologist Andréia Martins, the coordinator of field work for AMLD, said capturing tamarins in the wild is a job that requires time and patience. She is responsible for monitoring and capturing golden lion tamarins in the wild for the yellow-fever vaccination campaign, as well as vaccination efforts for captured golden lion tamarins. 

“The COVID-19 pandemic disturbed the beginning of vaccination a little. We missed the best time for capture but the work continues,” Martins said.

The small monkeys were captured and taken to a lab to receive the vaccine because the animals needed to be anesthetized to receive the inoculation and follow-up blood testing. The vaccine is administered just under the monkey’s skin, Ruiz Miranda explains. The golden lion tamarin’s skin is very thin and that’s why the animal had to be sedated so it would not move during the shot.

AMLD Executive Director Luis Paulo Ferraz said that the scientists tried to keep the golden lion tamarins together in their family groups when transporting them back and forth to the lab.

Scientists had discussed creating a field processing procedure so they wouldn’t have to take the animals to a lab but there were risks to that. “We thought about that and said, ‘It’s a new thing. It has all the recipe for going wrong,’” Ruiz Miranda said.

Bringing the animals to the lab allowed scientists to observe the animals and collect blood samples to see if the vaccine was working. Early results were promising. 

The scientists continued the work, capturing the tamarins again 30 days after the initial vaccination to measure the vaccine’s efficacy. 

As of January 2022, more than 200 tamarins have received the yellow fever vaccination and blood tests indicate that 92% of the vaccinated monkeys have developed antibodies to the disease, Martins said.

Freire credits the partners and supporters who assisted with these efforts. “If we had to do it alone, we wouldn’t have been able to do it,” he said.

Ongoing efforts

The project is still in its experimental phase and there is a three-year plan to inoculate a total of 500 golden lion tamarins, Martins said.

Ruiz Miranda said the hope is that as more monkeys are vaccinated, there will be a way scientists can develop a field processing procedure in which it’s not necessary to bring the animals back and forth to the lab.

Dietz said the vaccination efforts are ongoing while AMLD and its partners continue to learn more about the biology of the virus in the presence of people and non-human primates in the forests. He also said the project will require long-term funding. “I’m not sure when/if we will be able to say that we are done vaccinating GLTs against yellow fever,” Dietz said.

Andréia Martins carries the Olympic Torch in the name of Associação Mico-Leão-Dourado (Golden Lion Tamarin Association) through the city of Rio Bonito in 2016.

Adds Ferraz, “Our main concern now is related to the fact that we don’t know what are the possibilities of this crisis happening again.”

Meanwhile, the public can help support AMLD’s vaccination efforts by making contributions to the all-volunteer Save the Golden Lion Tamarin organization, with the funds going to support AMLD’s strategic plan to keep GLTs safe from extinction. 

AMLD and SGLT continue to provide zoos worldwide with up-to-date information on the progress of the yellow fever vaccination campaign.

Ferraz invites people to follow AMLD and SGLT on social media and to visit the Golden Lion Tamarin Ecological Park in Brazil when it is safe to do so. “It’s a fantastic experience in your heart and makes you feel part of this process,” he said.