STEVE INSKEEP, HOST:
This next story underlines how much we don't know about the Zika virus. That's the virus that's been linked to many birth defects - or so doctors think. NPR's Lourdes Garcia-Navarro traveled to the Brazilian city of Salvador, where researchers are trying to answer a question that seemed like it was already answered.
LOURDES GARCIA-NAVARRO, BYLINE: And that question is, is the Zika virus responsible for the rise in the cases of microcephaly that doctors are seeing across the country? So far, doctors suspect the link is there, but they're trying to prove it beyond a reasonable doubt. This week, director Antonio Raimundo de Almeida at the Roberto Santos General Hospital in Salvador, in the state of Bahia, gathered 16 mothers with their microcephalic babies for a battery of tests.
ANTONIO RAIMUNDO DE ALMEIDA: We do a full history. We do blood tests - everything. It's a full team
GARCIA-NAVARRO: In the waiting room, the mothers cradled their infants, who all have the telltale small cranium of microcephaly. To be clear, microcephaly is a symptom and not a disease. The condition happens when a fetus's brain doesn't develop in the mother's womb, so the skull doesn't expand to a normal size - hence the small head. And there are many things that can cause it, Dr. Almeida says.
ALMEIDA: Toxoplasmosis, cytomegalovirus, syphilis...
GARCIA-NAVARRO: ...As well as Rubella and genetic abnormalities. So first, they need to rule out that any of those have caused these cases of microcephaly. A team of six doctors - from a neuropediatrician to an ophthalmologist - have gotten a good look at large group of affected infants. And the doctors have made some startling discoveries. Suspected cases of Zika-related microcephaly have some unique markers.
In one of the rooms, Dr. Adriana Mattos examines 3-month-old Barbara Antonia, who has microcephaly.
ADRIANA MATTOS: (Speaking Portuguese).
GARCIA-NAVARRO: Dr. Mattos turns the child on her chest and points out that Barbara Antonia appears to be able to lift her head, and that she has unusual upper-body strength.
MATTOS: (Speaking Portuguese).
GARCIA-NAVARRO: But in fact, what she says is that in many of these Zika-related cases, the muscles in the upper body and neck are unusually stiff, which is very different than what we find in other infections that cause microcephaly, she says. Dr. Joao Ricardo de Almeida is a neuroradiologist, and he's been reviewing dozens of ultrasound brain scans of the microcephalic infants.
JOAO RICARDO DE ALMEIDA: You see, like, very profound abnormalities. Usually it's striking. It's really scary to look at, you know.
GARCIA-NAVARRO: He says mothers who were infected in the first trimester have infants who seem to suffer the most damage, and that kind of damage also appears to be different.
J. ALMEIDA: Regarding Zika, there seems to be some particular abnormalities that we do not see in, for example, toxoplasmosis or cytomegalovirus or rubella.
GARCIA-NAVARRO: If you look at a brain, which we've all seen, we have these ridges like coral, and these babies don't have that.
J. ALMEIDA: They don't. It's like a smooth rock.
GARCIA-NAVARRO: And he says the degree of damage that he's seeing will probably mean that rehabilitation will be very difficult.
J. ALMEIDA: They're not going to be functional. They're going to be having to, you know, be taken care of, like, for the rest of their lives.
GARCIA-NAVARRO: Dr. Albert Ko from Yale University has been collaborating with Bahia's study. He says while microcephaly is getting all the attention, the virus could be having a far wider range of effects on fetuses.
ALBERT KO: We are seeing cases in the hospital of children who have normal-sized heads but are having neurological lesions and eye lesions. And we're extremely concerned about that because that may suggest that these cases of microcephaly - those 4,000 cases - are just the tip of the iceberg.
GARCIA-NAVARRO: Children could appear normal, but may suffer a range of developmental delays, he says. In other words, scientists say, the deeper they investigate this outbreak, the more worrying it becomes. Lourdes Garcia-Navarro, NPR News, Salvador, Brazil.