In April 2018, employees of Associação Mico-Leão-Dourado, an NGO dedicated to protecting the species, found one of these endangered primates apparently sick and unable to climb trees.
He was lying on the forest floor in the municipality of Aldeia, about 80 kilometers from the capital of Rio de Janeiro.
The next day, field workers looked for the animal but could not find it in the middle of the forest. But, at the end of that month, the bodies of two other lion tamarins were discovered in nearby forests, in Cambucaes and Imbau.
The victimized animals immediately put environmentalists on alert.
On May 17, 2018, their worst fears came true: the first confirmed death of a golden lion tamarin from yellow fever was announced by the Ministry of Health and the Ministry of the Environment.
“Until this report, we didn’t know whether the animals were susceptible to the disease, even after four decades of working with lion tamarins.
But now we understand that they are even more susceptible than humans,” explains Dr. Carlos Ruiz, president of the Mico-Leão-Dourado Association.
A species at risk
Known for its characteristic “mane”, similar to that of a lion, and for its orange coat, the golden lion tamarin, or Leontopithecus rosalia, is a monkey endemic to the Atlantic Forest, a biome that is home to 22 of the 77 species of primates in Brazil.
In the 1980s, the species was critically endangered due to habitat loss and extremely high levels of poaching.
At the time, the population was reduced to just a few hundred individuals who inhabited isolated forest fragments around the São João River basin, in the state of Rio de Janeiro.
However, a successful campaign focused intensively on conservation actions, which saw the introduction of zoo-born tamarins into wild populations, increased the number of lion tamarins to 3,700 in 2014.
Then came the yellow fever outbreak, between late 2017 and early 2018. It was the biggest human epidemic in Brazil since mass vaccination began in the 1940s. , spread to the populous states of the Southeast, killing hundreds and infecting thousands.
Scientists, alarmed by the first yellow fever deaths of golden lion tamarins in 2018, were stunned by the 32% decline in the species due to the disease, a terrible loss for an animal already classified as endangered by the International Union for Conservation. of Nature (IUCN).
Compounding the crisis, there was an uninformed reaction by local residents to the yellow fever outbreak, with a series of attacks on all species of monkeys, apparently based on the false belief that lion tamarins, not mosquitoes, were capable of transmitting directly the disease to humans. Some primates were illegally killed by poisoning and others were shot.
More bad news: Research published in 2018 by Karen Strier, an anthropologist at the University of Wisconsin who has studied Atlantic Forest monkeys since the 1980s, and colleagues revealed that muriquis numbers have also suffered “catastrophic” declines in the Private Natural Heritage Reserve of the Atlantic Forest due to yellow fever, falling by 10% and 26% in two separate populations.
“The impact of yellow fever has been absolutely devastating” for these primates, especially lion tamarins, says Ruiz. “It could set conservation efforts back 30 years.”
He reports some good news: volunteers are now continuously monitoring surviving lion tamarin populations, helping local public health officials ensure nearly 100% vaccination of people in affected areas, and regularly exchanging information with government agencies to help to prevent future outbreaks.
Isolate epidemic or a permanent affliction?
It is believed that yellow fever originated in Africa and spread to Brazil as a result of the transatlantic trade of enslaved people.
The disease first appeared in Recife, in 1685, according to historical records. However, yellow fever is not endemic to most of the country and therefore most monkeys have not developed resistance to it, leaving them particularly vulnerable, according to the Brazilian Society of Primatology.
It is not known how, or when, lion tamarin populations will recover after this significant loss.
“The biggest problem is how these species recover from collapses,” says anthropologist Strier. “Either they reproduce within the surviving group or they need to recruit individuals from other populations.
But the more fragmented the landscape, the more difficult [this recruitment] is.” The problem with reproduction within a single group is that “if the population is small, it may not work, and it also produces less genetic diversity.”
Tragically, primate experts fear that yellow fever outbreaks could become a regular occurrence in the Atlantic Forest, and that the disease could become a new threat to the golden lion tamarin, while illegal trafficking remains a serious concern.
“From time to time, [yellow fever] re-emerges and may affect regions beyond the Amazon if the transmission is viable,” says a spokesperson for the Brazilian Society of Primatology. “But it could also become an endemic disease in the Atlantic Forest.”
A combination of climate change and deforestation in areas that serve as buffer zones between the rainforest and urban areas has allowed yellow fever to spread.
Logging and charcoal production, agriculture, and urbanization have devastated the habitat of the golden lion tamarin, reducing it to just 2% of its original Atlantic Forest area.
The promise of a vaccine
Hope now centers on a newly developed vaccine for non-human primates that could immunize species like the golden lion tamarin and perhaps save them from disease and help them avoid extinction.
Marcos Freire, a researcher at the Oswaldo Cruz Foundation in Rio de Janeiro, who worked on a team that produced a vaccine for yellow fever in humans, has been looking for an alternative for primates since 2017, and believes he now has one that might work.
“We would like to vaccinate some of these animals and then transport them back to areas where there has been mortality,” he says. “But no one has ever vaccinated a monkey species before and there are many challenges.”
Freire says he is applying for permission from the Ministry of Health and the Ministry of Agriculture to capture and immunize wild lion tamarin populations.
“In Brazil, until now there has never been a license to administer vaccines to non-human primates”, he says. “Dogs, cats, and cows, yes – but not primates.”
The vaccine, which he initially hopes to use in 500 primates, is based on a dilution of the yellow fever vaccine given to humans and uses a similar process and formula.
“We applied different amounts of doses to species from our primate center in Rio de Janeiro and the results were effective”, he reveals.
But practical challenges persist: how, for example, “to test it in animals that are critically endangered?”, asks Strier, who supports the development of the vaccine.
“And how do you administer it to animals in the wild in a cost-effective way? And what about the fact that there are humans who have not yet been vaccinated?”
Even if these hurdles are overcome, vaccination will not completely eliminate the disease because female mosquitoes pass the virus directly to their eggs.
Meanwhile, there are other promising solutions, such as neutralizing mosquitoes through genetic modification, as explored in the case of Zika virus; or using mathematical models to anticipate the arrival of the virus in various locations to combat it immediately.
The vaccine, if it proves effective, could offer important relief to these endangered primates, even as other human dangers put pressure on ecosystems in the Southeast.
Regardless of the results, vaccine research will offer “a good opportunity to learn from what happens,” concludes Freire.
“Do lion tamarins survive because they are immune or have they not been infected? Any kind of [observed] result will be important. Because, if every year we have another episode, we would have to go back to captive breeding.”