ANNAPOLIS, MD. – The scramble to learn exactly how and when after infection the Zika virus affects the developing fetus has put pregnant women at the center of an unprecedented infectious disease emergency response.
“It’s the most complicated infectious disease response we’ve ever done,” Dana Meaney-Delman, MD, of the Centers for Disease Control and Prevention, told an audience at the annual scientific meeting of the Infectious Diseases Society for Obstetrics and Gynecology. “It’s also the first time an emergency response team has included an ob.gyn.”
Although research into Zika virus is happening at breakneck speed, every finding seems to lead to still more questions. “It’s hard to keep up,” said Dr. Meaney-Delman, who is a Clinical Deputy on the Pregnancy and Birth Defects Task Force, part of the CDC’s Zika virus response.
What is known
What is known is that Zika virus is primarily vector-borne, either manifesting as a mild illness or remaining subclinical. The virus is also communicable through male-to-female sex, female-to-female sex, blood donation, and organ transplantation. Once infected, one is immune; if symptomatic, the presentation clears within a couple of weeks. If a woman is infected during pregnancy, it can be transmitted to the developing fetus, including at the time of birth, according to Dr. Meaney-Delman.
“We know transmission can occur in any trimester. We’ve seen it in the placenta, in amniotic fluid, in the brain, as well as in the brains of infants who have died,” she said.
Whether the virus poses a risk to the fetus around the time of conception is not clear, but Dr. Meaney-Delman said that since other infections such as rubella and cytomegalovirus do pose a risk, the CDC is issuing Zika guidance accordingly.
Despite an initial theory that pregnant women were more susceptible to Zika infection, there is no evidence to date confirming this, but “the combination of mosquitoes and sexual transmission really puts a woman of reproductive age at risk,” said Catherine Y. Spong, MD, who also spoke during the meeting. Dr. Spong is acting director of the National Institute of Child Health and Human Development, part of the National Institutes of Health.
Based on data derived from other flaviviruses, the “good news” is that infected nonpregnant women who later want to conceive do not have a higher risk of bearing a child with Zika-related complications, according to Dr. Meaney-Delman.
Abnormalities seen and unseen
During the initial stages of the Zika outbreak in Brazil, the spiking rate of babies born with microcephaly attracted the most attention; yet it is now apparent that children were also born with a growing list of other Zika-associated pregnancy outcomes that likely were missed at the time, according to Dr. Spong.
“That’s not to say that a child that doesn’t have microcephaly does or doesn’t have some of these other complications. We don’t know; they weren’t studied because they didn’t have the microcephaly,” Dr Spong said. “To get the data right, you need to follow all the children.”
Brain abnormalities such as ventriculomegaly and intracranial calcifications, as well as a range of growth abnormalities, miscarriage, and stillbirth are increasingly associated with infants born to infected women. Data is also beginning to link Zika virus to limb abnormalities, hypertonia, hearing loss, damage to the eyes and central nervous system, and seizures.
The World Health Organization has also noted the involvement of the cardiac, genitourinary, and digestive systems in babies born to infected mothers in Panama and Colombia. “The caveat [to these data], is that all these women were symptomatic,” Dr. Spong said, noting that in Brazil, where the outbreak was first documented, 80% of the infected pregnant women were asymptomatic during the pregnancy.
“Just because the mother has no symptoms, she’s fine? That doesn’t make any sense to me,” Dr. Spong said. “We know that infections in pregnancy can result in long-term outcomes in kids that you don’t have the ability to diagnose at birth. We need to be cognizant of this and we need to study it.”
Although initial theories were that viremia in symptomatic women was likely higher, thus imparting a higher risk of infection in their fetus, Dr. Meaney-Delman said the number of asymptomatic women whose fetuses are affected has debunked this line of thinking.
Risk of infection during pregnancy
As to what the actual risk of Zika virus infection is during pregnancy, “honestly we don’t know,” said Dr. Spong. “There are modeling estimates that [it’s] between 1% and 13% in a first trimester infection, but we don’t have the hard and fast data.”