Microcephaly: Details on the Alarming Birth Defect Linked to Zika Virus The rare birth defect is associated with the mosquito-borne Zika virus.

 -- At the center of the Zika virus crisis is the rise of a dangerous condition called microcephaly. The rare birth defect has affected thousands of infants in Brazil, leading officials to call up the military and hundreds of thousands of health workers to combat the virus, which is transmitted by mosquitoes.

What Is Microcephaly?

Microcephaly literally means small head, and infants are usually diagnosed if their head circumference is in the last 3 percent for infants of the same sex and age. Those with the defect often face a host of other symptoms related to the deformity.

These problems include seizures, developmental delays, hearing loss and vision problems, according to the Centers for Disease Control and Prevention.

"If the head is small, the brain is small and that means there’s something wrong," said Dr. Frank Esper, an infectious disease specialist at University Hospitals-Rainbow Babies & Children’s Hospital.

Until doctors do scans and developmental testing, it isn't immediately clear if a child will have significant developmental delays or if they will just have the significantly smaller head, Esper said.

How Often Does Microcephaly Happen?

In the U.S., the birth defect is extremely rare and affects about two to 12 infants out of 10,000 live births, according to the CDC.

What Causes Microcephaly

There are various reasons an infant would develop microcephaly in utero. There could be a genetic cause or the mother may have been exposed to a different infections, including rubella or toxoplasmosis, while pregnant.

Additionally, severe malnutrition or exposure to drugs and alcohol could increase the risk of giving birth to a child with microcephaly.

Last year, health officials sounded the alarm of an increase in microcephaly cases in Brazil that they connected to an increase in Zika virus cases.

Is There a Treatment?

There is currently no treatment or cure for microcephaly. In more severe cases, infants can get supportive care to help with other health problems such as seizures. Additionally, services such as speech or physical therapy to help with developmental delays can help children.

It's still unclear whether children exposed to the Zika virus will have many other developmental delays related to their microcephaly, Esper said.

"We know the developmental milestones for each of these children. The researchers will be able to look at their children and see if they are meeting their developmental milestones," Esper said. "I expect that in 2016, we will have a better idea about what it means for the child" to have Zika-related microcephaly.

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