O'Connor and Friedrich hope to answer important unknowns about the virus, including how long it's present after infection, where in the body besides the blood it exists, and what the likelihood is that an infected mother will pass it on to her offspring. They are also deviating from the ordinary method for disseminating research — publishing in a peer-reviewed journal — by posting their data for both their colleagues and the public to see as soon as it comes in.

That could be a problem.

"I am aware that sharing ultrasound imagery of developing macaques can elicit stronger emotions than looking at relatively sterile charts and tables. It certainly did for me and our staff who saw the first ultrasound today," O'Connor logged on the lab's website.

"I want to thank those who have viewed our data so far and have chosen not to use it out of context to further arguments against using animals in research."

This ultrasound shows the rhesus monkey fetus before the mother was injected with Zika two weeks ago. Researchers say ultrasounds show the fetus still appears healthy. (University of Wisconsin, Madison)

Last Thursday I asked him what he meant by "taking data out of context."

"The idea of making data from nonhuman primates available to the public is basically an invitation to disaster," he said, referring to the possibility that those who oppose animal research will use it in a propagandistic way. "Just like if you were to take patient data out of the hospital and show images of surgeries or ultrasounds ... without the full context of how you ended up in that position. It can be visceral, it can be grotesque."

O'Connor said that both he and Friedrich have had run-ins over the years with animal welfare activists.

"Madison is a very progressive city," he said. "We have a lot of people here who have very strong viewpoints, including a community of people who are pretty strongly against research on nonhuman primates in most contexts."

The issue of animal welfare has been a flashpoint at the university because of its status as a hub for animal research, and because it operates one of seven national primate research centers. In 2014, the school was fined $35,000 by the U.S. Department of Agriculture for violations of the federal Animal Research Act.

The two scientists' experiences researching AIDS/HIV have colored their opinions about using animals.

"I like to remind people that, even though you don't hear about it as much today, there’s still about 6,000 people who get HIV every day around the world," O'Connor says. "In the entire history of my lab and Tom’s lab and probably every other lab at this university ... we’re not going to use 6,000 monkeys in our entire scientific careers. So the idea that a small number of animals could have a profound effect on the health of a lot of people with HIV is something we came to terms with a long time ago."

Still, he said, injecting a pregnant monkey with the Zika virus was "profound."

"As parents ourselves we are sensitive to the implications of studying mothers during pregnancy," he says.

Friedrich said his first experiment as a Ph.D. student involved injecting monkeys with the simian immune deficiency virus, a retrovirus similar to HIV. "I went back with the veterinarians to assist with the process. I wanted to take ownership of it and see what it was going to mean for those animals, and it was a hard thing to do."

Animal Welfare Group Opposed

Last month, Cruelty Free International, a London-based, anti-animal experimentation organization with roots going back to 1898, came out against the experiments.

“While we support effective and humane research in the search for vaccines and treatments for Zika virus, we have serious concerns regarding the use of monkeys and other animals for this purpose," said Katy Taylor, the organization's director of science. "The poor relevance of using monkeys to study human disease and the greater relevance of human-based approaches, means that it is scientifically and morally indefensible to deliberately infect monkeys with Zika virus and/or to test therapies and vaccines on them.”

Friedrich said using animals is the best way to get the most relevant data quickly, and that human trials would cause significant delay.

"It will take a long time to enroll the number of people that would be required ... to conclude that it was statistically sound data that allows us to draw conclusions applicable to most infected people," he says.

He says taking the necessary samples from a monkey wouldn't be feasible or ethical in humans. "We might sample amniotic fluid from the infected [monkey] on a frequent basis and ask whether the virus gets into the amniotic fluid, and that’s just not something you can do in pregnant humans."

Jonathan Kimmelman, an associate professor in the biomedical ethics unit of McGill University, says it's "silly" to dismiss research results gleaned from animals as irrelevant to humans.

"There are some animal experiments that are reasonably predictive of scenarios that will play out in human beings and some [that] aren’t."

Friedrich points to trials in monkeys that found pre-exposure prophylaxis drugs (PrEP) are effective in preventing infection in people who are later exposed to HIV.

"This result paved the way for clinical trials of PrEP in humans that were also extremely effective," he said in an email. The result: Truvada, approved by the FDA in 2012 as the first drug to prevent people from acquiring HIV.

No Backlash -- Yet

As of last week, the lab had yet to experience a significant backlash for their experiment.

But, O'Connor said, "I’m under no illusion that's going to continue indefinitely."

In the meantime, at least one online criticism has emerged, on a website called "Primate Freedom," which attacks O'Connor for "using and killing monkeys."

"His career rests squarely on their corpses," the post says.

Kimmelman, the bioethicist, says the researchers' public dissemination of their data is a strong mitigating factor in justifying these experiments.

"The sad reality is that most of the research we conduct on animals never gets into the biomedical literature. The results are almost completely inaccessible," he says. "That kind of retention of data fails to redeem the suffering and the sacrifice of animals in experiments."

The real-time data-sharing aspect of their research has so far been a big success, says Friedrich, with other scientists using their posted data and replicating the results, or collaborating on certain tests.

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After Infecting Pregnant Monkey With Zika, Scientists Wait for Backlash