This article primarily covers the chronology of the 2015–16 Zika virus epidemic. Flag icons denote the first announcements of confirmed cases by the respective nation-states, their first deaths (and other events such as their first reported cases of microcephaly and major public health announcements), and relevant sessions and announcements of the World Health Organization (WHO), and the U.S. Centers for Disease Control (CDC), as well as relevant virological, epidemiological, and entomological studies.
The date of the first confirmations of the disease or any event in a country may be before or after the date of the events in local time because of the International Dateline.
UgandaThe Zika virus is first isolated in 1947 in a rhesus monkey in the Zika Forest near Entebbe, Uganda, and first recovered from an Aedes africanus mosquito in 1948.[4][5] Serological evidence indicates additional human exposure and/or presence in some mosquito species between 1951 and 1981 in parts of Africa (Uganda and Tanzania having the first detection of antibody in humans, in 1952,[6] followed by isolation of the virus from a young girl in Nigeria in 1954 during an outbreak of jaundice,[7] and experimental infection in a human volunteer in 1956.[8] The virus was then found variously in Egypt, Central African Republic, Côte d'Ivoire, Senegal, Sierra Leone, and Gabon;[citation needed] Between 1969 and 1983, Zika was found in equatorial Asia including India, Indonesia, Malaysia and Pakistan.[9] Zika is generally found in mosquitoes and monkeys in a band of countries stretching across equatorial Africa)[10] and Asia (Malaysia, Philippines, Thailand, Vietnam, and Indonesia).[11][12][13] The first confirmed case of Zika fever in a human occurs in Uganda during 1964 in a field researcher, who experiences a mild, non-itchy rash.[4]
Federated States of MicronesiaThe first major outbreak is identified outside of Africa and Asia, on Yap Island. Previously only 14 cases of Zika fever had been documented since the virus had first been identified in 1947.[11][14] Approximately 5,005 people, more than 70% of the population of 7,391, were infected with Zika, and generally exhibited mild symptoms; no cases of microcephaly were reported.[12]
United StatesThe first case of sexual transmission is reported, that of a scientist who had fallen ill in Senegal who thereafter infected his wife.[4]
Researchers identify two distinct lineages of the Zika virus, African and Asian.[4][10][15][16][17][18]
French PolynesiaIn October 2013, an independent outbreak of the Zika virus occurred in the Society, Marquesas and Tuamotu Islands of French Polynesia.[19] The outbreak abated in October 2014, with 8,723 suspected cases of Zika reported. The true number of Zika cases was estimated at more than 30,000.[20] An unusual rise in neurological syndromes is reported, including 42 cases of Guillain–Barré syndrome (GBS);[21] typically five cases are reported in a three-month timeframe.[22]
French Polynesia On 20 March, researchers discover that two mothers and their newborns test positive for Zika, perinatal transmission confirmed by polymerase chain reaction performed on serum collected within four days of birth during the outbreak.[4][23]
French Polynesia On 31 March, researchers on Tahiti report that 2.8% of blood donors between November 2013 and February 2014 tested positive for the Zika virus, of which 3% were asymptomatic at the time of blood donation.[24] This indicated a potential risk of transmission of the Zika virus through blood transfusions, but there were no confirmed cases of this occurring.[25]
French Polynesia On 13 December, a patient recovering from Zika infection on Tahiti seeks treatment for bloody sperm. Zika virus is isolated from his semen, adding to the evidence that Zika can be sexually transmitted.[4][26]
JapanIn December 2013, a Japanese tourist returning to Japan was diagnosed with Zika virus infection by the National Institute of Infectious Diseases after visiting the French Polynesian island of Bora Bora, becoming the first imported case of Zika fever in Japan.[27]
New CaledoniaIn January 2014, indigenous cases of Zika virus infection were reported in New Caledonia.[28] The outbreak peaked in April, with the number of confirmed cases reaching 1,400 by 17 September.[21]
Cook IslandsIn February 2014, an outbreak of Zika started in the Cook Islands. The outbreak ended on 29 May, with 50 confirmed and 932 suspected cases of Zika virus infection.[21][29]
Easter IslandIn March 2014, there were one confirmed and 40 suspected cases of Zika virus infection on Easter Island.[30]
BangladeshA human blood sample that was obtained in 2014 was confirmed to have Zika virus by Bangladesh's health ministry on 22 March 2016.[31]
Solomon IslandsAn outbreak of Zika begins on the Solomon Islands, with 302 cases reported by 3 May.[32]
Brazil On 2 March, an illness in Northeastern Brazil characterized by a skin rash is reported.[33] In 2015 alone the virus was detected in several other regions. Subsequent genetic analysis of Brazilian Zika genomes suggest that virus may have been circulating undetected for over 1 year in Brazil.[34]
VanuatuOn 27 April, the Vanuatu Ministry of Health reports that blood samples collected before March were confirmed to contain the Zika virus.[35]
BrazilOn 29 April, samples first test positive for the Zika virus.[10]
BrazilOn 15 May, the Ministry of Health reports the presence and circulation of the Zika virus in the states of Bahia and Rio Grande do Norte after testing 16 people for Zika.[36]
BrazilOn 17 July, neurological disorders in newborns associated with history of infection are reported.[10]
BrazilA sharp increase in the number of microcephaly cases is reported. The state of Pernambuco used to register 10 cases of microcephaly annually,[37] whereas in 2015 over 140 cases were registered.[38]
ColombiaOn 16 October, Colombia confirms, by PCR, its first autochthonous Zika cases.[39]
Colombia27 cases of Guillain–Barré syndrome are reported in the region around Cucuta; 27,000 cases of Zika are reported nationwide.[40]
Cape VerdeOn 21 October, Cabo Verde confirms, by PCR, its first outbreak of Zika.[41]
SurinameOn 2 November, Suriname reports its first two autochthonous cases.[42]
BrazilOn 11 November, the Ministry of Health declares a national public health emergency.[37][43]
United NationsOn 17 November, the Pan American Health Organization (PAHO), under the aegis of the WHO, issues an Epidemiological Alert regarding the increase in microcephaly cases in northeastern Brazil.[37]
French PolynesiaOn 24 November, French Polynesian authorities announce that there had been an unusual increase in the number of cases of central nervous system malformations in fetuses and infants, including microcephaly, following the 2013–2014 outbreak.[44][45]