Something is killing howler monkeys in Nicaragua. And nobody knows what it is.
Some conservationists speculate that the primates’ plight might be related to drought, food shortages or other environmental factors. But one leading primate expert thinks the monkey die-off could be an early warning sign for something far more serious: a new viral outbreak.
That’s because howler monkeys are super susceptible to mosquito-borne illnesses. Previous monkey die-offs were harbingers of yellow fever outbreaks in Central America in the 1950s, and more recently in Argentina in the late 2000s.
Yellow fever was eradicated in Nicaragua decades ago, but has since been replaced by other mosquito-borne viruses such as dengue, chikungunya and Zika, which this week was declared a global health emergency by the World Health Organization (WHO). Chikungunya has infected more than 100,000 people since arriving in Central America in 2014, and Nicaragua this week reported its first 15 cases of Zika, a virus that’s in the same family as yellow fever.
Primate specialists consulted by Fusion say they don’t know of any reported cases of howler monkeys contracting chikungunya or Zika, but the viruses are so new in the Americas that their greater effects are just being discovered. And given howler monkeys’ hypersusceptibility to yellow fever, experts say it’s not crazy to suspect that some primate populations are also suffering from the spread of related mosquito-borne disease.
“Non-human primates can contract Zika and chikungunya, although we don’t know anything about the symptoms or transmission rates in Neotropical primates,” conservation scientist Williams-Guillén, of Paso Pacifico, told Fusion. “Presumably yellow fever is no longer in Nicaragua, it is just that we know from the past when it was endemic that howlers were susceptible.”
Liliana Cortes-Ortiz, of the international Primate Specialist Group and a researcher at the University of Michigan, says “it could be possible” that primates and other howler monkeys in the Americas are becoming hosts for Zika, which was first discovered in a different species of monkey in Africa. But Zika is new to the Americas, and little is known.
Over the past few months, more than two dozen howler monkeys were found fallen in the tropical dry forest covering Nicaragua’s southern Pacific coast, according to a body count by Paso Pacifico, a non-governmental conservation group working in the area. Those are just the cases people know about. The real number of dead monkeys in the forest could be much higher, conservationists warn.
The dead monkeys that Williams-Guillén’s Paso Pacifico team has examined did not appear to be physically sick, she says. The dead monkeys were found with food in their stomachs and no signs of physical trauma, lesions or hemorrhaging. That suggests they didn’t die of starvation or injury, and that any illness they might have contracted was fast-acting, the wildlife expert says.
Williams-Guillén says her team is working with primate specialists from University of California, Davis to determine the cause of the mysterious monkey deaths. But she says the government would be wise to treat the matter as a potential canary in a coal mine.
Nicaraguan authorities, however, are downplaying the conservation group’s accounts of simian suffering. Government health and wildlife officials last week conducted a series of in situ visits to two coastal areas that reported recent monkey deaths and said they found nothing out of the ordinary. The monkeys populations they saw appeared healthy, and food and water supplies were fine, according to Nicaraguan zoologist and conservation expert Eduardo Sacasa, who accompanied the government team on the first site visit.
Government environment and health officials didn’t respond to requests for comment. They seldom do. But Nicaraguan academics are skeptical that the monkey deaths are linked to Zika. Manuel Orozco, executive director of the Nicaraguan Center for Health Studies and Investigations (CIES), says the first reported cases of Zika in Nicaragua have come from different parts of the country, suggesting its not related to the monkey deaths, which are clustered on the southern Pacific coast.
Still, something strange is happening. Williams-Guillén, who has been studying Nicaragua’s howler monkey population for more than 20 years, says she has “no doubt” that howler monkeys are dying of unusual causes. “I’ve spent years walking around the forest in Nicaragua and never came across a dead monkey before; now we’re coming across many,” she said.
Others have witnessed the phenomena too. One woman used her cellphone to capture a monkey writhing in the throes of death, and another man reportedly called Paso Pacifico to report that he saw a disoriented howler monkey stagger into the street and get hit by a car.
Whatever’s happening, it requires further study, Williams-Guillén insists. And to do that, scientists will need to collect tissue and hair samples from a recently deceased animal and get them to labs in the United States
“We will have to find relatively recently dead bodies of monkeys to collect the samples, so that is the challenge and main potential bottleneck,” Williams-Guillén said.
In the meantime, conservationists insist the howler monkeys are not a threat to humans. Indeed, it’s the other way around.
“Humans are the real threat,” says Sacasa, the Nicaraguan zookeeper.