Zika: A Timeline
1947: Scientists identify a new virus in rhesus monkeys in Uganda; first human cases detected in Uganda and Tanzania five years later.
2007: First large Zika outbreak in humans, on the Pacific island of Yap in Micronesia. An estimated 73 percent of residents become infected.
May 2015: Brazil confirms locally acquired Zika cases, the first time the disease has been found in South America.
October-November 2015: The virus spreads to the African island of Cabo Verde and at least six Central and South American countries.
November 2015: Brazilian officials declare a public health emergency after seeing an extreme uptick in microcephaly cases in newborns. Amniotic fluid from
two pregnant women in Brazil tests positive for Zika, indicating the virus can be passed from the mother to the developing fetus.
Dec. 31, 2015: U.S. reports its first locally acquired Zika case in Puerto Rico. At press time, the island had 29,462 cases, according to the CDC.
January 2016: The CDC detects Zika in the brain tissue of babies born with microcephaly. Brazil reports 3,893 suspected cases of microcephaly, including 49
deaths. More than a half-dozen more countries report cases.
February 2016: The World Health Organization declares Zika a global public health emergency. President Barack Obama requests $1.9 billion in emergency
funding to fight Zika. Congress refuses to approve the request.
The CDC confirms Zika can cause microcephaly and issues a public health alert.
May 2016: Puerto Rico reports its first microcephaly case linked to Zika.
July 2016: Two human vaccine trials begin, one led by the U.S. National Institutes of Health and a second by U.S. company Inovio Pharmaceuticals and South
Korean firm GeneOne.
July 29, 2016: Four cases of locally acquired Zika infection are reported in Miami-Dade and Broward counties in South Florida. Since then, there have been
a total of 139 cases of local transmission in the state.
Aug. 1, 2016: The CDC issues a travel warning that pregnant women should avoid a specific neighborhood in Miami, one of the first times the agency has done
this because of a disease outbreak in the continental U.S.
Aug. 12, 2016: U.S. government declares a public health emergency in Puerto Rico as a result of the Zika epidemic.
Sept. 6, 2016: WHO recommends practicing safe sex for six months to avoid transmission, based on findings that Zika can be detected in semen for several
Nov. 1, 2016: Stanford researchers report that Zika infection impairs male fertility in mice models.
As of November, there had been 30,000 cases of Zika virus infection, 3,268 pregnant women with evidence of Zika infection and 25 babies born with
Zika-related birth defects in the U.S. and its territories.