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SAN JUAN — Hordes of American scientists and health officials have descended on Brazil since the Zika epidemic first emerged there last year. But it’s here, in this island territory, where leading disease researchers from the US government can really throw the weight of all their resources on the problem.

Puerto Rico is, in some respects, a massive Zika laboratory. A very active one.​

“We have many questions that have a very urgent public health need to be answered,” said Tyler Sharp, acting head epidemiologist at the CDC’s dengue branch, which is based in San Juan. “We would much prefer to not have to ask them. But they need to be asked.”


Nearly 100 CDC scientists are in the territory now focused on the Zika response. Some work at the dengue branch; others have been brought in from CDC headquarters in Atlanta or from the Arboviral Disease Branch in Fort Collins, Colo.

Microbiologist Joan Kenney was one of those who flew in from Colorado. She and her colleagues are testing insecticides, trying to see which ones are still effective against the island’s ubiquitous mosquitoes.


The need to figure out what will fend off Aedes mosquitoes here is critical. Puerto Rico sees an estimated 33,000 live births a year — and a lot of women could be exposed to the Zika virus while they are pregnant.

“I’m very concerned that before the year is out, there could be hundreds of thousands of Zika infections in Puerto Rico and thousands of infected pregnant women,” CDC Director Dr. Tom Frieden, who recently traveled to Puerto Rico, said during a teleconference late last week.

Zika WIC Puerto Rico
Maria Elena Malaret, a nutritionist and dietitian, explains the Zika virus to Julimar Rivera, left, who is four months pregnant, and her friend Alexandra Ayala. Erika P. Rodriguez for STAT

Regina Simeone, an epidemiologist with the CDC’s National Center on Birth Defects and Developmental Disabilities, is working with counterparts in Puerto Rico’s department of health to set up a registry of pregnant women who have been infected with the Zika virus.

To date, 21 pregnant women are known to have contracted the virus, the health department said Friday in its weekly release of Zika statistics. When pregnant women test positive for the virus, they are referred for ultrasound tests. According to Sharp, “We have not heard of any abnormal findings by ultrasound yet.”

The idea behind the registry, Simeone told STAT, is to mine the medical records of infected women to glean as much information as possible about their pre-pregnancy health and the health at birth of any previous children.

Then, the health of mothers and children born to them will be followed forward. Studying these mother-infant pairs should shed light on what Zika infection in pregnancy can provoke, in terms of birth defects, and how often they occur. For instance, it may indicate how frequently stillbirths happen after Zika infection.

“In terms of pregnant women, we think we can answer many — maybe not all — but many of the questions that we may have about microcephaly, relative risk, those sorts of things,” said Sharp. The island’s strong health care system and CDC’s partnership with the health department will assist in the effort, he noted.

Another CDC study will aim to answer key questions about how long people who are infected with Zika continue to emit the virus in body fluids. People who have contracted Zika and who agree to take part in the study will be asked to give a variety of body fluids at various times after they first became sick.

Saliva, urine, semen, and vaginal secretions will all be tested to see if diagnostic tests that use each fluid work better than the current approach, testing blood. It’s already thought the virus is found only briefly in blood but lingers longer in urine and saliva.

Sharp said semen and vaginal secretions will also be studied to get a better handle on how big a role sexual transmission plays in the spread of Zika.

And the researchers won’t merely look for traces of Zika, but actual infectious copies of the virus. Traces — or what is known as “defective interfering particles” — can’t pass on infection. Only whole, live viruses can.

The outbreak in Puerto Rico should additionally offer insights into the suspected link between Zika infections and Guillain-Barré syndrome, a form of progressive paralysis that is normally temporary. Puerto Rico has reported only one case of Guillain-Barré in a Zika patient, to date. But a large outbreak could bring many more.

Zika WIC Puerto Rico
Educational material about the Zika virus at a San Juan mall. Erika P. Rodriguez for STAT

French Polynesia reported a twentyfold increase in the prevalence of Guillain-Barré in 2013-14 during a major Zika outbreak there. Nine countries or territories have reported either an increase in cases linked to Zika outbreaks or Guillain-Barré in people who have tested positive for the virus.

In some cases, the phenomenon has been studied retrospectively, looking backward after the fact. But the plan in Puerto Rico is to quickly identify any patients with Guillain-Barré and follow them in real time to hopefully pin down whether Zika infection is responsible.

Other work planned for Puerto Rico includes trying to figure out how best to help people here combat Zika. Frieden said it is clear that before any programs can be rolled out on a large scale, they need to be piloted first.

For instance, there have been discussions about whether to offer to install screens on the homes of pregnant women; many dwellings in Puerto Rico do not have them.

A recent pilot test revealed what seems like a simple — if not cheap — way to protect pregnant women may not be so easy to put into operation.

Some people didn’t want screens because of the perception they obstruct the breezes that cool homes, Frieden said. Others, he noted, have open eaves, in which case screens on the windows “would have little or no impact.”