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CDC Provides Updates on Zika-Related Birth Defects

It has been more than 50 years since an epidemic resulted in as many birth defects as the Zika virus. To address this epidemic, the second in a series of six teleconferences, hosted by the Centers for Disease Control and Prevention (CDC), discussed Zika infection during pregnancy as well as subsequent birth defects.

To elaborate on the top areas of interest and challenges that health officials faced, the Centers for Disease Control and Prevention (CDC) hosted their second in a series of six teleconferences that discusses Zika infection. This teleconference discussed Zika infection during pregnancy as well as subsequent birth defects.

Sonja A. Rasmussen, MD, MS, director of the CDC’s Division of Public Health Information Dissemination and editor in-chief of the Morbidity and Mortality Weekly Report noted that although 4 in 5 Zika-infected adults are asymptomatic, the resulting complications in pregnant women and their fetuses are historical. She stated that it has been more than 50 years since an epidemic, the Rubella epidemic of the 1960s, resulted in as many birth defects as the Zika virus.

Zika virus has been detected in amniotic fluid, placenta, fetal and infant brains, and products of conception. The CDC officially confirmed a link between microcephaly and Zika infection after an unprecedented increase in cases immediately following the detection of Zika in Brazil in 2015. Zika infection around the time of fetal conception or during pregnancy can result in stillbirths, a decrease in the total amount of brain tissue, which would result in microcephaly, brain damage due to calcium deposits in the brain, excess fluid in the brain, irregular development of one or both eyes, and hearing impairments. Other common effects include:

  • Seizures
  • Trouble swallowing
  • Hypertonicity and posturing
  • Contractures which include club foot and joint curving
  • Severe irritability
  • Delays in development
  • Growth abnormalities Intrauterine growth restriction Head size not in proportion to length and weight

Dr. Rasmussen noted that there are still many unanswered questions regarding Zika infection in pregnant women. As a result, the CDC has launched three data collection initiatives: US Zika Pregnancy Registry, for pregnant women in the United States; Zika Active Pregnancy Surveillance System, for pregnant women in Puerto Rico; and Proyecto Vigilancia de Embarazadas con Zika, for pregnant women in Colombia. These programs are a collaboration between the CDC and state, tribal, local, and territorial health departments. They aim to monitor both pregnant women and their fetuses and to inform expecting mothers of clinical guidelines and infection prevention methods. The surveillance registries will monitor:

  • Pregnant women diagnosed with Zika infection Infants born to these women
  • Infants with lab evidence of congenital Zika infection whose mothers did not test positive for Zika Mothers of these infants

In response to the impending threat of active Zika transmission in the Continental US and Hawaii, the CDC is:

  • Increasing lab capacity for testing to identify Zika virus infection
  • Assisting in development of Zika detection tests
  • Collaborating with partners to control vector populations
  • Providing infection prevention recommendations
  • Building state capacity to identify babies with Zika-related birth defects

Janet Cragan, MD, MPH, medical officer in the CDC’s National Center on Birth Defects and Developmental Disabilities, delved into the details of microcephaly. She noted that there is currently no single accepted definition of the abnormality, since clinicians are using different cut-off points for diagnosis: head circumference less than third, fifth, or tenth percentile in comparison to infants of the same age and sex. However, during the teleconference, the CDC provided the listeners with a “Zika-related definition of congenital microcephaly,” which is divided into two parts, definite and possible:

  • Definite Live births Head circumference (HC) at birth <3rd percentile for gestational age and sex, OR If HC at birth is not available, HC <3rd percentile for age and sex within the first 6 weeks of life, adjusted for gestational age if preterm Stillbirths and Elective Terminations HC at delivery <3rd percentile for gestational age and sex
  • Possible Live births If an earlier HC is not available, HC <3rd percentile for age and sex beyond 6 weeks of life All Pregnancy Outcomes Microcephaly diagnosed or suspected on prenatal ultrasound in the absence of available postnatal HC measurements

Dr. Cragan also identified three distinct types of microcephaly:

  • Disproportionate- the infant’s head is disproportionate to the weight and length, but is normal for its age and sex
  • Proportionate- the infant’s head, weight, and length are too small for its age and sex, but are in proportion to each other
  • Relative microcephaly- the infant’s head size is within normal range for its age and sex, but is disproportional to its weight and length.

It was noted that infants born with microcephaly can expect a lifetime of cognitive and neurological impairments.

Dr. Cragan also discussed the importance of monitoring the prevalence of microcephaly. The CDC suggests that cases be divided by severity, known cause, and unknown cause. Suggested sources for data collection included areas where births and elective terminations occur (including home births), and hospitals and clinics where these infants are treated; the importance of reporting details specific to each case (in terms of the observed abnormalities) was also stressed.

Dr. Cragan also went on to describe Fetal Brain Disruption Sequence (FBDS), which was observed before 1984, but not officially described until then. FBDS is described as “brain destruction resulting in [the] collapse of the fetal skull, microcephaly, scalp rugae, and neurological impairment.” It was noted that this phenotype was observed in Zika-infected infants in Brazil.

At the completion of the teleconference, both Dr. Rasmussen and Dr. Cragan answered questions regarding Zika and microcephaly. One question posed during the teleconference was whether the rumor that the rise in microcephaly cases in Brazil was due to exposure to a chemical in pesticides was true. It was explained that this theory has no relevance since the pesticide in question has been in use for years, which would beg the question, why are we seeing the increase in the number of congenital microcephaly cases now? Furthermore, this theory would not explain the birth defects seen in fetuses of mothers who were infected with the Zika virus either through travel to a country where there is active transmission or through sexual contact with an infected male.

It was noted that the CDC does not know exactly how long Zika stays in the body, however, based on similar viruses and history of infections, for men, Zika can remain in bodily fluids (which can be transmitted to sexual partners) for up to 6 months, while for women it can stay in the body from 1 week to 10 days; however, it is recommended that women postpone conception for up to 8 weeks after the passing of a Zika infection.

Although Zika virus RNA has been detected in breastmilk, there are no known cases of viral transmission through breastfeeding. The CDC recommends the continuation of breastfeeding infants since the “benefits far outweigh the small risk of infection.”

The importance of communicating the threat of the Zika virus to the general public, informing them about the importance of reporting Zika symptoms or observed complications, and providing them with infection prevention methods continued to be emphasized. For any clinical concerns regarding Zika, the CDC will answer all questions emailed to ZikaMCH@cdc.gov. More information regarding microcephaly can be found on the CDC page, or the National Birth Defects Prevention Network page.