Is the Zika Virus (or Something Worse) Killing Nicaragua’s Monkeys?

Scientists fear that dozens of dead monkeys found in recent weeks may indicate the spread of a mosquito-borne pathogen.

A spider monkey near Cocibolca Lake in Granada, Nicaragua. (Photo: Alfredo Estrella/AFP/Getty Images)

Feb 3, 2016· 2 MIN READ

John R. Platt covers the environment, wildlife, and technology and for TakePart, Scientific American, Audubon, and other publications.

What the heck is killing Nicaragua’s monkeys?

Over the past couple of months, dozens of dead or dying monkeys have turned up in southwestern Nicaragua. The sick animals have displayed extreme lethargy or convulsions and have quickly perished after being discovered.

“A lot of signs point to some sort of pathogen being responsible,” said Kimberly Williams-Guillén, director of conservation science for Paso Pacifico, a nonprofit working in the area.

Pathogens that could be affecting the primates include mosquito-borne illnesses such as chikungunya, dengue fever, and the Zika virus, which the World Health Organization this week declared a global health emergency. So far only about a dozen people in Nicaragua have been diagnosed with Zika, but it is heavily present in neighboring countries.

Other possible causes for the monkey mortalities include drought or toxins. The region is experiencing a drought, and Williams-Guillén theorized that if any of the monkeys’ normal food sources are not available, “they could start eating something else that’s potentially toxic.”

None of the dead monkeys collected showed obvious signs of illness or damage. “If anything, I was struck by what good conditions the monkeys appeared to be in,” Williams-Guillén said. She reported that one monkey she autopsied showed no obvious signs of dehydration or emaciation. Another dead monkey examined last week by a Mexican veterinarian who specializes in primates had no obvious external signs of trauma or infection. “The animals seemed to be in good condition other than being dead,” she said.

So far most of the dead animals have been mantled howler monkeys. “Howler monkeys are one of the more abundant wildlife species in the region,” Williams-Guillén said. “They’re not shy about being near human communities because they’re not hunted. They’re not even pests. Nobody bothers them; they don’t bother anybody else.”

Additional deaths have come among two rarer species, white-faced capuchins and black-handed spider monkeys. Paso Pacifico has worked the past few years to conserve the spider monkeys, which are critically endangered in Nicaragua.

Williams-Guillén expressed concern that the number of dead monkeys that have been found does not convey the scope of the problem because finding a recently dead animal is a rare event. “Animals tend to get scavenged or decompose very quickly in tropical environments,” she said. “I’ve spent years of my life walking around forests in Nicaragua, and I’ve never just found a dead monkey just lying around. We have people finding dead and dying monkeys throughout the zone. It’s very unusual.”

Paso Pacifico has applied to the Nicaraguan government for emergency funding and hopes to bring in additional experts to do a rapid assessment to figure out what is killing the animals. DNA tests, for example, may reveal any possible viruses. Examinations could also reveal if the dead animals are a harbinger of a potential public health crisis that could affect people living near them.

Viruses would be hard to treat, as there are no antiviruses for Zika, chikungunya, or dengue for humans, let alone for animals. Drought could be easier to solve, at least in the short term. “We could put in emergency temporary watering holes,” Williams-Guillén said, which would let the animals stay hydrated.

For now, though, the main focus is on mobilizing resources to resolve the mystery. “All we can say is there is unusual mortality, and we want to figure out what’s going on and take steps to resolve it,” she said.