Most individuals infected with Zika virus experience mild or no symptoms. About 25% of infected people develop symptoms 2-10 days after infection, including rash, fever, joint pain, red eyes, and headache. Recovery is usually complete and fatalities are rare.
Two conditions associated with Zika virus infection have made the outbreak potentially more serious. The first is development of Guillain-Barré syndrome, which is progressive muscle weakness due to damage of the peripheral nervous system. The association of Guillain-Barré was first noted in French Polynesia during a 2013 outbreak.
Congenital microcephaly has been associated with Zika virus infection in Brazil. While there are other causes of microcephaly, there has been a surge in the number of cases during the Zika virus outbreak in that country. Whether or not Zika virus infection is responsible for this birth defect is not known. One report has questioned the surge in microcephaly, suggesting that it is largely attributed to an ‘awareness’ effect. Current epidemiological data are insufficient to prove a link of microcephaly with Zika virus infection. Needed are studies in which pregnant women are monitored to see if Zika virus infection leads to microcephaly.
Given the serious nature of Guillain-Barré and microcephaly, pregnant women should avoid traveling to areas that are endemic for Zika virus infection, or to take measures to reduce exposure to mosquitoes.