Zika virus has circulated in areas of Africa and Southeast Asia but was not known to cause large outbreaks. In 2007, it caused an outbreak in a new region, Yap Island in Micronesia. In 2013, the virus caused an even larger outbreak in French Polynesia. In May 2015, the Pan American Health Organization issued an alert regarding the first confirmed Zika virus infection in Brazil. Since that time, Brazil and other countries and territories in Central and South America, as well as the Caribbean (including Puerto Rico and the U.S. Virgin Islands) have experienced ongoing Zika virus transmission.
The first cases of locally transmitted Zika virus in the continental United States were confirmed in Florida in July 2016 followed by Texas in November 2016. Other cases in the continental United States were in people infected during travel to areas where Zika is circulating. In addition, returning travelers infected with Zika have passed the virus on to their sexual partners.
Pregnant women infected with Zika virus can pass the infection onto their babies during pregnancy or around the time of birth. During fetal development, Zika virus can cause a serious birth defect of the brain called microcephaly, a condition in which a baby’s head is abnormally small and can be associated with incomplete brain development. Additionally, Zika virus has also been associated with other fetal development problems, including eye defects, hearing loss, and impaired growth.
In June 2016, NIAID and other National Institutes of Health Institutes launched the Zika in Infants and Pregnancy (ZIP) trial. The study aims to enroll as many as 10,000 pregnant women at up to 15 sites. Participants will enroll in their first trimester of pregnancy and will be followed throughout their pregnancies to determine if they become infected with Zika virus and if so, what outcomes result for both mother and child. The participants’ infants will be carefully followed for at least one year after birth.
In rare cases, Zika infection may also lead to Guillain-Barré syndrome (GBS). GBS is an autoimmune disorder in which damaged nerve cells cause muscle weakness and, sometimes, partial or complete paralysis. Most people recover from GBS but some have permanent damage. In rare cases, GBS leads to death.