Albert Ko, an epidemiologist and infectious disease expert at the Yale University School of Public Health, has been studying Zika virus and its link to birth defects in newborns in Brazil. The mosquito-borne virus is suspected in a huge increase in cases of microcephaly, a rare condition in which babies have unusually small heads and damaged brains.

Ko spent December in Salvador, Brazil’s third largest city, working with researchers from the Oswaldo Cruz Foundation, a branch of that country’s health ministry, and from the University of Texas Medical Branch in Galveston. The team was investigating microcephaly cases at three maternity hospitals.

The Washington Post spoke with Ko on two occasions; his answers have been edited for clarity and length.

What has your research found so far at these three hospitals?

We are still in the middle of our investigation. We strongly believe that the cases of microcephaly we are identifying during this outbreak are due to Zika virus.

However, there are important caveats. First, it’s very likely that because of the high surveillance, we’re identifying cases that would not normally be reported or identified. Secondly, we still need to confirm that Zika virus is causing the large majority of the cases. Brazilian researchers have shown that Zika virus can cause congenital infections, and they have detected the virus in tissues of stillbirths as well as fetuses with congenital malformations.

But for the large majority of cases that have been reported as microcephaly, we still don’t have firm evidence.

This is one of the primary objectives of our research.

How many babies have been born with suspected cases of microcephaly at these hospitals?

We have identified both stillbirths and live births. We have identified 100 live births. But not all of those [cases] may be caused by Zika. We are trying to rule out other common causes, such as prematurity and congenital infections, including toxoplasmosis (an infection caused by a parasite commonly found in cat feces or cat litter).

Can you describe the different kinds of birth defects you’re seeing?

We’re seeing a spectrum. Many have fairly severe central nervous system lesions. There are also a lot of calcium deposits. … Those can cause seizures and cause impairment in terms of function for the brain.

We’re also seeing that in some babies, the brains, which usually have wrinkles, are actually smooth. That’s a sign that development of the brain has been impaired. Several of them are also impaired with respect to vision and hearing.

What else are you finding?

It seems like microcephaly may just be the tip of the iceberg. The preliminary evidence is that [some] babies who don’t have microcephaly may also have neurological lesions or birth defects that are not as obvious as microcephaly. We’re really concerned because of Zika, but we need to rule out other causes of congenital infection to really make sure.

How are the parents and families handling the stress and anxiety?

Obviously there’s a large amount of fear, especially among pregnant women. … For many people, the level of anxiety is extremely great. People want a birth. It’s one of the greatest pleasures or expressions of love in a person’s life. …

For many of the families, it really hasn’t hit yet what the future is going to be. Not all the brains are severely compromised. Some of the babies, now one month or two months old, they’re feeding, they’re growing.

There is a wide mix of emotions. Some families are in denial. Some are just devastated. All of the physicians are just feeling the enormous weight of seeing this unfold, the uncertainty of what has caused this and what the future holds for these babies. There’s a strange heaviness across all the physicians.

Once individuals are infected, do they have immunity for life?

We know so little. We presume that like other flaviviruses, except for dengue, if you’ve been exposed, you will have long-term immunity to being reinfected.