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Only months ago, the world’s knowledge about the Zika virus was pretty paltry.

So scant, in fact, that Dr. Tom Frieden, director of the Centers for Disease Control and Prevention, tweeted a picture of what he called “50 years of neglect” — a modest pile of scientific papers, not much thicker than a slim paperback. That was the sum total of Zika science.


In the intervening weeks, researchers in labs the world over have shifted their focus to the Zika virus — and that work is already gleaning results. Meanwhile, the virus’s march through the Americas is adding real world epidemiological evidence to bolster our understanding of what humankind can expect from Zika.

Many mysteries remain. But here are some things we’ve learned.

1. Yes, Zika infection during pregnancy can lead to brain-related birth defects in a fetus

For months, experts were cautious about linking the virus to birth defects. They really don’t have any doubt anymore: Zika has joined the list of viral infections that can cause birth defects if contracted during pregnancy.


Outside the research world, skeptics continue to ask why microcephaly, a condition in which newborns have abnormally small heads, hasn’t been seen elsewhere. Zika, after all, has been around for decades. The truth is that the condition has been seen elsewhere (including French Polynesia, which experienced a Zika outbreak in 2013-2014), and will likely be seen in more places with increasing frequency in the coming months.

A woman in Hawaii who spent the early part of her pregnancy in Brazil gave birth to a baby with severe microcephaly. A woman in Slovenia who, likewise, spent the early part of her pregnancy in Brazil terminated her pregnancy after tests showed significant birth defects, including microcephaly and fluid buildup in the brain.

Panama had informed the World Health Organization that Zika virus was found in a microcephalic infant. Born prematurely, it died shortly after birth. Colombia and Cape Verde have also recorded microcephaly cases, but are still checking to see if they are linked to Zika infection. Martinique may have joined the list.

The numbers outside Brazil are still small. But Zika arrived in other countries later than it did in Brazil. So the full consequences of infection during pregnancy won’t be seen in other parts of Latin America until the summer and fall, experts predict.

2. This isn’t just about microcephaly

While an explosion in the number of microcephaly cases in Brazil first alerted health authorities to possible complications from Zika, researchers now recognize that the virus can wreak other kinds of damage on developing fetuses.

Dr. Karin Nielsen-Saines, who is studying a cohort of women in Brazil who were infected during pregnancy, said microcephaly isn’t even the most common problem her team has seen. More frequent are brain calcifications — signs of brain tissue death. Another common observation is something called in utero growth restriction — babies that aren’t premature but are born unusually small. It’s as if they were starved in the womb, Nielsen-Saines told STAT.

Researchers from Brazil and the United States have also reported finding vision-threatening eye lesions in 10 of a group of 29 microcephalic babies they examined.

One of the authors, Dr. Albert Ko, of Yale University, is concerned that Zika-induced brain damage may be found in babies who don’t have microcephaly — babies whose mothers may initially believe they have dodged Zika’s blow. His group has also diagnosed hearing problems in some babies, Ko said.

Other, more subtle problems are likely going to come into view over time, Dr. Anthony Fauci warned in a recent talk on Zika. “That’s just the way congenital abnormalities work,” said Fauci, director of the National Institute of Allergy and Infectious Diseases.

It’s hard to prove, because miscarriages are common and occur for lots of reasons, but it is thought Zika infection during pregnancy may also increase the risk of late-term fetal loss.

3. Zika is an STD

In 2008, an American researcher got infected with Zika while doing fieldwork in Senegal. A short while after his return home, his wife — who hadn’t left the US — was sick too. The mode of transmission was sex, an unexpected discovery that earned the couple a spot in the medical literature.

The assumption was that sexual transmission of Zika was probably a rare event. Mosquitoes are the main culprit for the spread of this virus.

But the world’s recent experience with Ebola — a virus that can linger in testicles for months and is emitted in semen — made public health officials look more closely at the possibility of sexual spread of Zika.

In early February, the Dallas health department reported a case of a person whose partner had returned, infected, from South America. Since then, five more people in the US are believed to have been infected through sex. Argentina, Italy, France, and New Zealand have also reported cases of sexual transmission.

This is no longer a medical oddity. It’s a real public health concern, in part, because it increases the risk that women who are pregnant or might become pregnant could become infected.

4. Politicians may have global health fatigue

The Obama administration asked for $1.9 billion to finance the US Zika response. But the Republican-dominated Congress says there is unused Ebola response money the administration should use first.

The impasse is hurting the country’s ability to respond, Fauci and Frieden, the CDC director, have said. Congress held firm, heading off for a long Easter break without blinking.

Fauci warned this could have real implications for the development of a vaccine. It could spook off the pharmaceutical industry, critical players in this kind of work. “Uncertainty about funding, and how much we’re going to put in, and how much we’ll be able to do really brands us a little bit, if not a lot, like an unreliable partner,” he said.

The WHO is also having trouble raising funds for its Zika response. It’s asked for $25 million to fund its Zika efforts and those of its Americas division, the Pan American Health Organization. It’s received $3 million and is in negotiations for another $4 million.

The European Commission has released about $11 million for Zika research. Britain is spending about $5.7 million. A quarter of that is from the Wellcome Trust charity.

5. Mosquitoes are not our friends

OK, we already knew that.

But of all the misery these blood-sucking menaces spread — malaria, yellow fever, dengue, chikungunya, West Nile virus, Japanese encephalitis, St. Louis encephalitis, La Crosse encephalitis, Venezuelan encephalitis, and more — congenital birth defects are a new low.

Mosquitoes are nasty.

Follow the Zika virus through time and space

It might seem like the Zika virus exploded out of nowhere in Brazil a few months ago, but the virus has been all over the world since it was discovered in Uganda in 1947. Use the button to manually navigate the globe through the years, or drag your cursor to rotate it, and click on countries to discover the distribution of the Zika virus infection and associated neurological disorders across time and geographies, starting in 1947.