SILVA JARDIM, Brazil (AP) -- At a small lab in Brazil's Atlantic rainforest, researchers with gloved hands and masked faces weigh four tiny golden monkeys so a veterinarian can gently insert a needle under the thin skin of each sedated animal's abdomen.
The next morning, biologist Andréia Martins takes them to exactly where they were caught. She opens the wire cages and the monkeys scoot out, hop to a tree or onto the ground, scale the canopy and regroup as a family. They chat loudly as they disappear into the rainforest.
This brief, strange encounter with humanity was for their own health - and the survival of their species. These endangered wild monkeys, known as golden lion tamarins, have now been vaccinated against yellow fever, part of a groundbreaking campaign to save an endangered species.
"Vaccinating wildlife for the good of animals, not to protect humans, is novel," said Luís Paulo Ferraz, president of the nonprofit Golden Lion Tamarin Association.
When yellow fever began spreading in Brazil in 2016, resulting in more than 2,000 human infections and around 750 deaths, it also quickly killed a third of high-risk tamarins, most of them within months. So scientists in Brazil have developed a yellow fever vaccine for the endangered monkeys.
The vaccination campaign started in 2021 and more than 300 tamarins have already been vaccinated. The first such attempt in Brazil - and one of the first in the world - raises fundamental questions about how far one has to go to save a species from extinction.
One of the traditional conservation adages is “let it be”. But at a time when every corner of the earth is being affected by human impact — from melting icebergs to fragmented forests to plastic-filled oceans — a new generation of scientists and environmentalists are calling for increasingly more intrusive approaches to saving wildlife and ecosystems.
"There are people who say we shouldn't touch nature, that we shouldn't change anything. But really, there are no more pristine natural habitats," said Tony Goldberg, a disease ecologist and veterinarian at the University of Wisconsin-Madison who supports vaccination of wild animals when it's safe and practical. "People are becoming aware of the scale of the problem and realizing that they need to do something."
Carlos R. Ruiz-Miranda, a conservation biologist at the State University of Northern Rio de Janeiro, is among the scientists who have worked to protect golden lion tamarins for more than three decades, twice rushing to their rescue when they were threatened with extinction . He says vaccination is the only option left: "Is it too extreme? Give me another alternative.”
"We have to intervene when it's a man-made conservation risk, if you want an environment with wildlife," Ruiz-Miranda said.
Viruses have always existed in abundance in nature. But humans have drastically altered the conditions and impacts on how they spread throughout wildlife. Epidemics can spread across oceans and borders faster than ever before, and species already declining from habitat loss and other threats are at greater risk of being wiped out by outbreaks.
"Human activities absolutely accelerate the spread of disease in nonhuman populations," said Jeff Sebo, an environmental researcher at New York University who was not involved with the Brazil project.
But there are risks. It's hard to decide which species will get the attention and resources needed to survive. In Brazil, a political climate of fear of the COVID-19 pandemic and misinformation about vaccines in general have caused delays. But if scientists get it right, they could be pioneers in showing what's possible to save endangered wildlife.
The story of the golden lion tamarins is an epic saga — one that Marcos da Silva Freire, a longtime Brazilian public health official, experienced first-hand.
When Freire was a child in the 1960s, he spent weekends at his family's estate in the Atlantic Forest. But he has never seen golden lion tamarins.
Around this time, Brazilian primatologist Adelmar Faria Coimbra-Filho first sounded the alarm about the declining tamarin population. Habitat loss and poaching for the pet trade had reduced their numbers to just 200 in the wild.
Southeast Brazil was once covered by rainforest, but today the rolling landscape is an uneven checkerboard of dark green jungle and grassy cow pastures – only 12% of that rainforest remains.
Yet it is the only place on earth where wild golden lion tamarins live.
Efforts to save the charismatic monkeys — famous for their copper-colored fur and small, inquisitive faces framed by silky manes — led to a groundbreaking captive breeding program coordinated by around 150 zoos worldwide, including the Smithsonian National Zoo in Washington, D.C These animals were then carefully released in Brazil starting in 1984 in cooperation with local landowners.
When approached by researchers, Freire's father, a landowner, told them to coordinate with his son, who was then a veterinary medicine student in his mid-20s.
On a clear July morning, Freire walks a dirt road on his property, rays of light breaking through palm fronds. "The first monkeys were released around here, over that hill," he said, gesturing from the shore of a small lake, recalling that afternoon almost 40 years ago.
He smiled as he saw some of their offspring, two monkeys hopping along a swaying vine. They jumped onto a high branch and soon disappeared in a green kaleidoscope.
The reintroduction was a learning process, for both the scientists and the monkeys, he recalled. It was usually the second generation, not the first, that learned to be successful again in the wild.
Thanks to these efforts—and subsequent campaigns to replant and connect rainforest plots—the tamarin population slowly recovered, reaching about 3,700 by 2014.
But any celebration was premature.
On a foggy winter morning, Andréia Martins donned a camouflage jacket, rubber boots and a face mask and tucked her machete into her belt. She followed a narrow trail through the rainforest, stopping periodically to whistle in imitation of monkey contact calls.
Martins has been tracking golden lion tamarins in the rainforest for almost forty years. The longtime Golden Lion Tamarin Association biologist can discern the tiny glimmer of golden fur beneath a green canopy and recognize more than 18 different vocalizations — from alpha males' specific calls to their mates to different sounds to alert young monkeys to different ones Ways to draw attention to food and predators.
On this hike, she recorded the noisy encounter between two families of monkeys, about a dozen animals, cackling loudly to proclaim their territory.
Because of their patient fieldwork, which has recorded detailed population data for four decades, the researchers were even able to track how many tamarins were being killed by the yellow fever virus when it began circulating.
After the first laboratory-confirmed death of a tamarin from yellow fever in 2018, her team's census showed that the population of wild tamarins had dropped from 3,700 to about 2,500.
In the Poço das Antas Biological Reserve, one of the largest contiguous forest areas where they live, the death toll was even higher: a population of about 400 tamarins dropped to just 32. "They just weren't there anymore," she recalled itself.
The tamarins had again fallen victim to human encroachment. From the top of a wooden watchtower it is possible to see parts of the replanted rainforest as well as the newly upgraded BR101 highway which brings a steady flow of traffic to the region.
"This epidemic spread very quickly from north to south, across the country — no wildlife does that," Ruiz-Miranda said. "It's people. They overcome long distances in buses, trains, planes. They bring the disease with them.” Yellow fever is transmitted by mosquitoes, he explained, but highly mobile infected people spread the disease much further and faster than insects alone.
“We have lost 32% of the wild population. It was a tragedy - it showed us how vulnerable this small population is," said Ferraz of the nonprofit Golden Lion Tamarin Association.
"We realized that if we don't do anything, we could lose the entire population in five years."
Through a twist of fate, Marcos da Silva Freire had specialized in viruses. At the time of the yellow fever outbreak, he was deputy director for technological development at Brazil's Oswaldo Cruz Foundation, which oversees vaccine diagnostics and production in the country.
Conservationists, who had campaigned to protect the monkeys for decades, were at odds over whether to vaccinate them. Some hoped the virus would not affect the monkeys; others feared that any kind of novel intervention would be too risky.
But Freire decided to test an idea. He arranged with the Rio de Janeiro Primate Center that trials of different doses of yellow fever vaccine on about 60 monkeys, close relatives of tamarins, should begin in January 2018.
A year later, he checked the antibody levels in her blood - the vaccine seemed to be working, with no negative side effects.
Freire began devising a plan for the tamarins. "The idea is to vaccinate 500 animals," he said. "The aim is to vaccinate 150 animals and later take blood samples - to test safety and effectiveness."
The biologists had already refined a technique to lure the wild monkeys into baited cages. "It sounds like a cliché, but monkeys eat bananas," said scientist Ruiz-Miranda.
But finding official approval for something Brazil has never done before, vaccinating a wild species, has not been an easy process. And then COVID-19 struck.
When the team finally received government approval to begin vaccinating wild monkeys, Freire oversaw the initial rounds of vaccinations.
So far they have vaccinated more than 300 tamarins and found no adverse side effects. When they caught monkeys and retested them, 90% to 95% showed immunity - similar to the effectiveness of human vaccines.
The outbreak appears to have subsided and the monitored monkey population has stabilized overall and even increased slightly within the Poço das Antas Biological Reserve. And now the golden lion tamarins stand a better chance of survival than symbols of the Atlantic Rainforest.
While authorities elsewhere have vaccinated animals to protect human health — feral dogs and wild animals like raccoons have been vaccinated against rabies and other diseases — it's still very rare for scientists to give vaccine injections to directly protect an endangered species.
There was the campaign launched in 2016 to vaccinate endangered Hawaiian monk seals against a strain of the morbillivirus. And rabies vaccines have been given orally, hidden in food, to the endangered Ethiopian wolf and some other species.
Martin Gilbert, wildlife veterinarian and epidemiologist at Cornell University, explored another potential vaccination campaign by modeling the number of Amur tigers in Russia that would need to be vaccinated to protect against canine distemper. "Infectious diseases pose a threat to the conservation of wild species, and these will only increase as populations become more fragmented and isolated," he said.
Of particular concern are cases where encounters between humans or domesticated animals and wild animals directly transmit disease to threatened species, such as respiratory diseases and great apes. Several studies have shown that chimpanzees living near human settlements are more likely to suffer from several diseases.
"There's a lot of debate now about whether there is a ticking time bomb before wild ape populations become infected with COVID, and it sweeps through groups and kills many apes," said Goldberg of the University of Wisconsin-Madison.
Nevertheless, other scientists urge caution with any type of new intervention.
“What are the unintended consequences of vaccination? You can't always be sure," said Jacob Negrey, a biologist and primatologist at Wake Forest University's School of Medicine. "That would be my greatest hesitation - have we adequately controlled every single variable?"
James Dietz, a biologist and president of the US-based non-profit organization Save the Golden Lion Tamarins, was initially suspicious of Brazil's vaccination campaign. "If we choose to vaccinate wild animals against a disease, we may give them an advantage over unvaccinated animals - and by doing so we may be acting against natural selection, which over time would improve the genetics of the species," he said .
But in the end he overcame those concerns. "It wasn't until I realized the level of mortality that I realized we had to do this," he said. "And I'm very happy with the direction we've taken."
There are other reasons to be cautious. While golden lion tamarins are tiny — weighing less than 2 pounds — and can be lured into cages with banana bait, it's more difficult with large carnivores. "Capturing wild tigers and providing a vaccine is extremely difficult," said Dale Miquelle, who directs the global tiger program at the nonprofit Wildlife Conservation Society.
Still, his organization recommends that "for small and high-risk populations, it's a good idea to get vaccinated" against canine distemper. Nobody has tried it yet.
In Australia, scientists have applied for permits to begin a field trial to vaccinate wild koalas against chlamydia, which in some populations infects up to 80% of animals, causing death and reducing fertility.
The potential downside? "Capturing koalas is really stressful for the animals," said Samuel Phillips, a biologist at Australia's University of the Sunshine Coast. "It's a good balancing act between stressing them out and trying to help."
But increasingly, he and other scientists feel that through habitat loss and other environmental changes, "we've reduced their population so much that it's already at a critical point."
His conclusion: "We must do more to ensure that they survive."
Follow Christina Larson on Twitter at@larsonchristina
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