An epidemic of Zika fever, caused by Zika virus, began in Brazil and affected other countries in the Americas from April 2015 to November 2016. The World Health Organization (WHO) declared the end of the epidemic in November 2016, but noted that the virus still represents "a highly significant and long term problem". It is estimated that 1.5 million people were infected by Zika virus in Brazil, with over 3,500 cases of infant microcephaly reported between October 2015 and January 2016. The epidemic also affected other parts of South and North America, as well as several islands in the Pacific.
Zika virus spread to Brazil from Oceania in 2013 or 2014. Brazil notified the WHO of an illness characterized by skin rash in March 2015, and Zika was identified as the cause in May 2015. In February 2016, the WHO declared the outbreak a Public Health Emergency of International Concern as evidence grew that Zika can cause birth defects as well as neurological problems. The virus can be transmitted from a pregnant woman to her fetus, and can cause microcephaly and other severe brain anomalies in the infant. Zika infections in adults can result in Guillain–Barré syndrome. In approximately one in five cases, Zika virus infections result in Zika fever, a minor illness that causes symptoms such as fever and a rash. Prior to the outbreak, Zika was considered a mild infection, as most infections are asymptomatic, making it difficult to determine precise estimates of the number of cases.
