On Wednesday, April 13, the Centers for Disease Control and Prevention (CDC) officially confirmed that the mosquito-borne Zika virus can cause microcephaly, a congenital defect marked by an abnormally small head, and other fetal brain abnormalities. The Zika outbreak had previously been linked with unusually high rates of microcephaly, but it had not been demonstrated that the virus could actually cause the birth defect. The CDC report establishes that when pregnant women contract Zika, the virus can definitely bring about microcephaly. In other words, it’s causation, not just a matter of correlation.
“This study marks a turning point in the Zika outbreak,” Tom Frieden, M.D., M.P.H., director of the CDC, said in a statement announcing the news. Cases in this Zika outbreak were first reported in Brazil in May 2015. To date, the virus, which is usually spread by the Aedes aegypti mosquito species but can also be sexually transmitted, has cropped up in 62 countries and territories, according to the World Health Organization. There have been 346 reported cases in the U.S., all from people returning from travel in affected areas; seven of those were sexually transmitted and none have been due to mosquito bites in this country, says the CDC.
Symptoms of Zika include fever, joint pain, rash, and pink eye, although only 20 percent of those affected show signs of infection. In addition to microcephaly, which can cause developmental delays, hearing problems, and seizures, Zika has also been connected with Guillain-Barre syndrome, an autoimmune neurologic disorder that can bring about paralysis of varying severity.