Epidemiology

A total of 87 countries and territories have reported current or previous Zika virus transmission, including Africa, the Americas, South-East Asia, and the Western-Pacific region, as of July 2019.[17]

Zika virus was first discovered in the Zika forest of Uganda in 1947 in rhesus monkeys, but was not identified in humans until 1952 in Tanzania.[18][19] Since then, outbreaks have occurred sporadically in Africa, the Americas, Asia, and the Pacific. Until 2007, only 14 cases had been documented in humans worldwide.[20]

The first large outbreak was reported on the island of Yap (Federated States of Micronesia) in 2007.[21][22] The most likely source of this outbreak was introduction of the virus by travel or trade involving an infected person or an infected mosquito.[1] Another large outbreak was seen in the Pacific Islands (French Polynesia, Easter Island, the Cook Islands, New Caledonia) in 2013 to 2014. This was the first outbreak where congenital malformations (e.g., microcephaly) and neurologic complications, including Guillain-Barre syndrome (GBS), were linked to the infection, although this association was made retrospectively.[21][23][24]

In 2015 to 2016, a large outbreak occurred in the Americas triggering a public health emergency. At the height of the outbreak in 2016, over 200,000 cases were reported in Brazil - the focus of the outbreak - with over 8000 babies born with malformations related to Zika virus infection. The incidence peaked in 2016, has declined substantially since then, and is now considered to be over.[25] In the US, limited local transmission was reported in Florida and Texas in 2016 to 2017, but no cases have been reported since then. Despite the outbreak being over, Zika virus infection is, and will continue to be, a risk in many countries in the Americas and around the world. 

The 2015 to 2016 outbreak in the Americas resulted in an increase in travel-associated cases globally, including the US, UK, Europe, Australia, New Zealand, Israel, Japan, and China.[26][27][28][29][30][31][32][33][34] Travel-related cases have been declining in US states since 2017, with 72 cases reported in returning travelers in 2018, and only 5 cases reported as of 01 August 2019.[35] In the UK, 4 travel-associated cases were reported in 2018, a significant decline from the 283 cases reported in 2016. One case of likely sexual transmission has been reported in the UK in 2016.[36]

Although the pandemic has waned, there are continued reports of outbreaks in Asia, India, and Africa.[37] An outbreak was reported in India in November 2018; however, transmission is no longer ongoing.[38] Autochthonous transmission was reported in France in October 2019. This is likely the first episode of local vector-borne transmission detected in metropolitan France and in Europe.[39]

An association between Zika virus infection and fetal microcephaly, as well as other birth defects, was first reported in the outbreak in the Americas in October 2015.[40] The prevalence of birth defects potentially related to Zika virus infection was reported to be 3 per 1000 live births in a birth cohort of nearly 1 million births in 2016.[41] Data from the US Zika Pregnancy Registry found that 10% of pregnancies with laboratory-confirmed infection resulted in fetuses/infants with birth defects. This figure increases to 15% when restricting the analysis to the first trimester.[42] This report covered cases reported in US states only. A more robust study of completed pregnancies in women with laboratory evidence of Zika virus infection in US territories found approximately 1 in 20 (5%) fetuses or infants had a possible Zika-associated birth defect. When the analysis was restricted to confirmed infection in the first trimester, the rate increased to 1 in 12 (8%).[43]

An association between Zika virus infection and GBS was first reported in the outbreak in the Americas in July 2015. Current evidence estimates the incidence of GBS to be 24 cases per 100,000 persons infected with Zika.[44] 

CDC: Zika virus case counts in the US external link opens in a new window

PLISA health information platform for the Americas: Zika external link opens in a new window

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