Pandemic delays critical vaccine for endangered golden lion tamarins

The rampant spread of COVID-19 across Brazil is threatening more than half a century of conservation efforts to protect a small, bright orange monkey called the golden lion tamarin.

Named for their leonine manes and found only in Brazil, golden lion tamarins had shrunk in number to a mere 200 in the 1970s, because of their capture for the pet trade and the destruction and fragmentation of their Atlantic Forest habitat. A series of efforts—ranging from genetic and reproductive research to captive breeding and relocations to habitat areas needing the biggest population boost—brought their numbers back up to about 3,700 by 2014. (Read about the creation a wildlife corridor in the Atlantic Forest to help golden lion tamarins cross a busy highway and enter new territory.)

Then, another setback: a 2017 outbreak of yellow fever killed some 30 percent of their restored numbers. Now, a years-long effort to vaccinate the monkeys against yellow fever has been put on hold because of the coronavirus pandemic.

“It was a surprise that the tamarins died” of yellow fever, says Russ Mittermeier, chief conservation officer at the nonprofit Global Wildlife Conservation, who has been studying the golden lion tamarin since the 1970s. Other monkey species were known to be susceptible to the disease, but not golden lion tamarins. “Another outbreak would be disastrous.”

It was mid-2017 when the golden lion tamarins started to disappear.

Carlos Ramon Ruiz-Miranda, a primatologist at the State University of Northern Rio de Janeiro and his colleagues were finishing a routine survey of the tiny monkey’s population. Brazil was in the midst of its worst yellow fever outbreak in 80 years, which had swept across the country’s southeast, killing more than 250 people and thousands of monkeys in the Atlantic Forest.

When Ruiz-Miranda couldn’t find any of the golden lion tamarins in the Poço das Antas Biological Reserve, a main region of study since 1985, he felt disconcerted.

“I felt worried and a little bit scared because it’s a big population, and there was this sudden realization that something bad had happened,” he says.

Soon, locals started calling the researcher about sick golden lion tamarins lying on the ground, unable to climb trees. (Read about the golden lion tamarins stolen from European zoos in recent years.)

“It’s really rare to find dead golden lion tamarins just lying in a pasture,” says Ruiz-Miranda, who is also the president of the nonprofit Golden Lion Tamarin Association, a Brazil-based conservation group. The monkeys tend to stay in the forest, only crossing pastures briefly when going from one forest fragment to another, and their carcasses disappear quickly because of the predators and high humidity where they live. “In all the years I’d worked with them, I’d never seen that before.”

In May 2018, scientists confirmed the first golden lion tamarin death from yellow fever. The following year, a study showed just how dire the situation was; the yellow fever outbreak caused the population to drop by almost a third, to just 2,516 monkeys left today. At the Poço das Antas Biological Reserve in Rio de Janeiro, researchers did eventually confirm that 30 golden lion tamarins were still living there, but the reserve’s population had plummeted 70 percent.

Ruiz-Miranda and others from the Golden Lion Tamarin Association and Save the Golden Lion Tamarin, a U.S.-based charity, decided a vaccine was their best chance to save the species.

In many cases, vaccinating entire populations of primates would be impossible, but golden lion tamarins live in a small region and are closely tracked by researchers, so it seemed feasible, says Sérgio Lucena, a primatologist and director of the National Institute of the Atlantic Forest. To be successful, he says, “the vaccine has to be used in a very exact way and within a very restricted area.”

After the first round of vaccines—a diluted version of what is administered to humans—was given to golden lion tamarins in captivity and deemed safe, the biggest hurdle was getting permission to give it to the monkeys in the forest. This was the first time such a request had been made to the government, and there was no clear process for getting it approved.

Then, just as Ruiz-Miranda and his team were waiting for one last permit before heading into the field to vaccinate five of the monkeys’ social groups, the COVID-19 pandemic hit.

Stuck working from home and unable to head into the field to continue their work, the researchers have lost seven months waiting.

“We were very frustrated and irritated with the bureaucracy,” says Ruiz-Miranda. “We were making weekly calls to try to get something going with the vaccination and to have a quick response to the realization we had lost the tamarins.”

Finally, their insistence got them what they needed in August. Permit in hand, they’re ready to head back into the field this September. Once the first groups are vaccinated and transferred, they’ll be observed for six months to a year before others get the same treatment.

To protect the researchers from the spread of COVID-19, they will now travel to the forest in teams of two, requiring more vehicles and increasing the time and costs needed to carry out their work. Just three will be allowed in the lab at once, and they will wear masks all the time, not just while handling the monkeys. (There’s no evidence golden lion tamarins can get the coronavirus from humans, but there’s also no evidence they can’t.)

It takes up to three days to find the golden lion tamarins that are monitored with telemetry; those without radio transmitters can take two months to track down. Once found, they are put in a special trap where they are sedated to take blood samples, swabs and perform a full health check. The yellow fever vaccine can be administered with the monkeys awake.

If all goes well, the goal is to vaccinate 500 golden lion tamarins, the minimum viable population to keep the species alive in the wild. Ruiz-Miranda hopes the time they lost to COVID-19 hasn’t already taken a toll on the population’s health.

“The smaller the population, the higher the probability that any small catastrophic event could wipe them out,” he says. “If nothing is done, we could start seeing local extinctions.”