Skip to Main Content

MADISON, Wisc. — Walk into most macaque enclosures, and you might expect a ruckus: bird-like cooing if you’re bringing them food, or guttural barks if you aren’t.

But these 13 monkeys didn’t make a sound.

They were used to visitors, and on a day in early June, when the door cracked open, the one with the red scar hardly even looked up. At that point, she was something of a celebrity. Anyone with an Internet connection could click through every aspect of her life; her pregnancy was as headline-worthy as Janet Jackson’s.


She was among the first pregnant lab monkeys to be infected with Zika virus, and two days earlier, she had been the first to come to term. Now, she was back in her cage, as all of her bodily fluids — and every part of her fetus — were being tested for traces of the virus.

Primate research is usually slow and secretive, its protocols vetted and tweaked and vetted again before being carried out by a special team of veterinarians and technicians. But as more and more Zika-infected women start giving birth to babies with defects, a handful of labs — including the one here at the University of Wisconsin, Madison — have fast-tracked the process.


“Because Zika is a public emergency, you have to be rushed … you can’t afford to have a vaccine only 50 years from now,” said University of California, Los Angeles, researcher Dr. Karin Nielsen-Saines, who is studying how the virus affects pregnant women in Brazil. “It’s very frustrating when you see a disease that you can’t do anything about,” she added. “It’s very difficult for everyone involved.”

These experiments could help to eliminate that frustration — after all, one of the most widely prescribed HIV drugs was discovered through research on the same species, the rhesus macaque, by some of the same scientists.

David O’Connor’s lab
Researchers in David O’Connor’s lab at the University of Wisconsin, Madison, analyze human plasma samples containing the Zika virus. Kristi L. Hall

Yet the pace of this Zika research is also daunting: Researchers are using the monkeys to learn as much about the virus as they can — but they’re still figuring out whether Zika even affects macaques in the same way it affects humans.

David O’Connor, the leader of the University of Wisconsin’s Zika project, had hardly even heard of the virus until October 2015. He was at a conference in Brazil to talk about his other work — most of it on HIV — when a Brazilian colleague pulled him aside. “He said they had these babies being born with small heads,” O’Connor recalled. “He and others had suspected it was a virus.”

Could O’Connor help?

Soon, his team was receiving vials of the virus isolated from around the world, and preparing to inject it into the folds of monkeys’ skin. Would they sicken? Would the virus affect them at all? The researchers had no idea.

They weren’t the only ones intrigued by Zika: So many scientists wanted to collaborate on the project that O’Connor couldn’t figure out how to loop them all in without hours wasted assigning passwords.

Then he had an idea: Why not just post everything they found online for public use? Other researchers could use the data to avoid unnecessarily repeating experiments that had already been done. Vaccine makers could look to the data for real-time updates. Interested laypeople could get a glimpse inside the often-hermetic world of biomedical research as it tries to elucidate a public health emergency.

Since then, the California and Oregon National Primate Research Centers, as well as the nonprofit biomedical institute Southern Research, were inspired to start sharing data from their own Zika-infected macaques.

The question — for the researchers and for everyone — was: How well could a relatively small number of monkeys reproduce the biology that is driving the Zika outbreak?

The Zika room

To enter the restricted areas of the Wisconsin National Primate Research Center, you need to take off your street clothes. You then slip into a three-piece suit of scrubs, stretch water-resistant covers over your shoes, snap on two pairs of gloves, pull on a hairnet, and strap a mask around your ears, pinching it tight over your nose. As if that weren’t enough, you also shield your face with a visor that looks like it might’ve been borrowed from the riot police.

That isn’t, in fact, enough for the Zika room. There, you have to shimmy into a white full-body Tyvek suit.

The getup is as much to protect the monkeys from human germs as it is to protect us from theirs. But on the door is a forbidding orange sign: “Warning: pregnant women should not enter.”

Zika Ultrasound
Researchers at the Wisconsin National Primate Research Center perform a fetal ultrasound on a pregnant rhesus macaque to study the link between the Zika virus and birth defects, and to try to develop a Zika vaccine. Justin Bomberg/University of Wisconsin-Madison

In many ways, the macaques in the Zika room are no different from those elsewhere in the lab. They too listen to Top 40 radio to replace the auditory stimulation of a forest or a New Delhi suburb. They too are given chains of cut PVC piping into which the staff has frozen a mixture of yogurt, juice, fruit, and cereal, so that the monkeys can indulge their dinnertime habits, picking at sweet ice crystals the way they might at grubs in a rotten log. They too twist the mirrors tied to their cages to make threatening displays across the room, using eye contact to establish a hierarchy as rigid as any military platoon.

Their bodily fluids are a different story, though.

For 10 days after being injected with Zika, the monkeys were anesthetized daily through the bars of their cages and carried to a table in the corner of the room. There, on sterile cloths, they had their blood drawn and their saliva soaked up with a sponge. These samples were packed alongside vials of urine and feces into a cooler and driven four miles to David O’Connor’s lab, where a researcher would send out a mass email: “Blood is here, come and get it!”

Then, the sequencing began.

In males and non-pregnant females, the researchers found virus in the blood for a few days after infection. After that, the virus seems to have been beaten back by the monkeys’ immune systems. When they were re-infected with a different strain, the virus was undetectable in their blood and urine.

“Getting infected is like being vaccinated,” Saverio Capuano, the assistant director of animal services, said through his mask and visor. He gestured around the room to all the monkeys that were scampering around their cages, potentially immune. “That’s what we’re hoping will happen in downtown Rio de Janeiro.”

The pregnant females, though, presented a mystery when first injected with the virus — a mystery that had also been observed in humans: The virus seemed to be lingering in their blood.

“There are a couple of different interpretations,” said Thaddeus Golos, a pregnancy expert at University of Wisconsin who is collaborating with O’Connor on the Zika project. “One might be that in pregnancy the maternal immune response is somewhat compromised. … Another possibility, though, is that the placenta and the fetus became infected and continued to release virus into the bloodstream.”

The monkey with the red scar hadn’t had the prolonged presence of virus in the blood — perhaps because she was infected during the third trimester instead of the early stages of pregnancy, when Zika appears to wreak its worst damage. But the virus’s presence in her body was no less mysterious.

On June 1, when she was in the operating room for a C-section, the surgeons sampled a bunch of her tissues to analyze in the lab.

Still lurking in her lymph nodes and her spleen were traces of virus, even though it hadn’t been detectable in her blood for weeks and weeks. O’Connor wasn’t sure how to explain it.

“We’re treating it like a mistake; someone somewhere messed something up,” he said two days later, as he emerged from a huddle of researchers trying to figure out what to make of the results. “It hadn’t been on our radar as something we had to look for in these animals. Until it was.”

Mapping a virus

It wasn’t a mistake.

O’Connor’s group took more biopsies from other, non-pregnant monkeys 70 days after they had been first infected, and found traces of the virus in both their lymph nodes and their spleens.

That didn’t necessarily mean that those monkeys were still able to transmit the virus: It could just have been bits of genetic material left over after a battle between Zika and the immune system.

But researchers in Oregon found the virus in lymph nodes, the spleen, joint tissues, and the urinary tract a few days after it had disappeared from the blood — and it was live virus, not just traces of genetic material.

Earlier on, the scientists had also seen traces of the virus in the nervous tissue of the spinal cord and the sciatic nerve, a possible explanation for the link between Zika virus and a paralysis-causing neurological condition called Guillain-Barré syndrome.

Taken alone, each of these results can seem almost meaningless, like trying to make out an entire van Gogh from a single stroke of paint. But taken together, they start to provide a map of the virus’s hiding places, which can be essential for stopping the damage caused by the disease.

“For the development of vaccines and therapeutics, it’s really important to know where the virus is and how long it’s staying there, so we can measure the efficacy,” said Daniel Streblow, a virologist who is studying macaque models at the Oregon Health and Science University.

Just as important as stopping the spread of Zika from one body to another is preventing it from being transmitted across the placenta and into a fetus. It’s done with remarkable success in HIV with a combination of potent drugs.

Because Zika is most dangerous for fetuses, a drug that has a similar effect on Zika could diffuse much of the panic surrounding the outbreak.

To look for such a drug, though, researchers need an animal model that accurately reproduces how the virus sneaks across the immunological checkpoint that is the human placenta.

It looks like the macaque may be that animal model. On June 22, the Oregon team performed a C-section on a fetus that had been looking abnormal for weeks. They are now trying to figure out whether that abnormality is microcephaly, a brain-damaging birth defect that has been linked to Zika in humans. The Wisconsin team is also racing to analyze fetal tissue samples — and their pathologist is busy fixing even more onto microscope slides.

For the scientists, the urgency around the Zika research is exhausting — “The last six months will go down as the most stressful ever in the 10-plus years I’ve had a lab,” said O’Connor — but there is exhilaration in his voice when he discusses the work.

Even on a late Friday afternoon on a terrace overlooking Lake Mendota, while swimmers shimmied off the edge of a dock and families lined up for bratwursts, O’Connor and the other researchers here kept talking Zika.

For a while, the conversation drifted to soccer: That night, the US would play Colombia, and academic collaborators from each country were sporting rival colors. But soon, they were back on the virus: why transmission was reported in Rio but not Sao Paulo, how contraception is illegal in some of the most affected countries.

One grad student, Brock Bakke, listed the ravages of other infectious diseases: millions of deaths, horrible cancers caused by viruses, debilitating fevers.

Yet here they were, drinking beer, poring over the mysteries of a virus they hardly knew about before this past fall.

“A bunch of scientists were like, ‘You can kill millions of us, you can give us cancer,’” Bakke said, bouncing his 5-month-old on his lap. “‘But don’t mess with our babies.’”