Zika outbreak: Monkey study suggests infection lasts longer in pregnancy than thought

Among the first surprising results: While most people harbourZika in their bloodstream for only a week or so after infection, thevirus lingered in one pregnant monkey's blood for 70 days and inanother for 30 days.

We are in a race against the virus, arace against time.-KoenVanRompay

Rhesus macaque monkeys make a good model for studying how Zikainfects people, researchers at the University of Wisconsin-Madisonconcluded Tuesday in Nature Communications. But what's novel is thatthe team is posting its raw data online right away even ultrasoundimages of developing monkeys that they acknowledged at the time"can elicit stronger emotions than looking at relatively sterilecharts" so that normally competing research labs can worktogether to speed discoveries.

A handful of other labs have joined in the movement to sharetheir own data from Zika-infected monkeys in real time.

The Zika virus, which is spread mainly by a tropical mosquito, iscausing an epidemic in Latin America and the Caribbean. It causesonly a mild illness, at worst, in most people but can cause severebrain-related birth defects if woman are infected during pregnancy.

Protective vaccine hints

O'Connor's team gave monkeys a skin jab with a strain of Zikavirus to mimic a mosquito bite. Tuesday's paper compiles resultsfrom eight animals. Much like people, the six non-pregnant monkeyscleared Zika out of the bloodstream fairly quickly, in about 10days.

And when researchers attempted to infect them with the samestrain 10 weeks later, they didn't get sick evidence that itshould be possible to design a protective vaccine, O'Connor said.

"We don't know how long this immunity lasts," cautioned studyco-author Dawn Dudley, but that's a key question for women incountries hard-hit by the virus.

Elsewhere on Tuesday, mice given a single shot of one of two experimental Zika vaccines were completely protected when exposed to the virus one to two months later. It's a promising sign that similar vaccines under development for humans will protect against Zika, U.S. researchers said.

"Thenew mouse model should be useful for comparative assessments of the large range of vaccine candidates now being designed," said Professor Adrian Hill, director of Oxford University's Jenner Institute, which did not conduct the mouse study but is also developing Zika vaccines.

In the mouse study, published in the journal Nature, a team led by Dr. DanBarouch of Beth Israel Deaconess Medical Center and Harvard Medical School,tested two different vaccine candidates in a strain of mice that develops Zikasymptoms.

One candidate, a DNA vaccine, was developed by Barouch and colleagues. Itcontains bits of genetic material from a Zika virus strain from Brazil.

The other was made from a purified but inactivated version of the Zika virusfrom Puerto Rico. That vaccine was developed by researchers at Walter ReedArmy Institute of Research in Silver Spring, Md.

Does longer viruspresence inblood relate to birth abnormalities?

Mice given either type of vaccine were 100 per cent protected from Zika after asingle shot. Unvaccinated mice that were exposed to the virus all developedsymptoms of Zika.

Both types of vaccines DNA and inactivated virus vaccines have beensuccessfully developed to prevent infection from viruses related to Zika,including West Nile and dengue.

"We need to be cautious about extrapolating data from a mouse model intohumans," Barouch said. But the fact that the vaccines protected mice and thattheir antibodies protected other mice from Zika was grounds for optimism overthe development of a Zika vaccine, he said.

Another big issue with the monkey research is why the two pregnant monkeys, infected duringthe first trimester, had infections linger drastically longer something reported so far in only one human case, which ended inabortion.

When those monkey babies are delivered by C-section andeuthanized next month, their tissues and placenta will be carefullyexamined for Zika. One theory is that if a fetus is infected, itwill pump virus back into mom's blood, O'Connor said.

"We might hypothesize that the pregnancy with the longestduration of extended viremia is more likely to have abnormalitiesdetected at birth, but right now that's simply a hypothesis," hecautioned.