Epidemiology

A total of 92 countries and territories have reported current or previous Zika virus transmission, including Africa, the Americas, South-East Asia, the Western-Pacific region, and one country in Europe (France), as of May 2024.​[18]

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.[19][20] 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.[21]

The first large outbreak was reported on the island of Yap (Federated States of Micronesia) in 2007.[22][23] 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.[22][24][25]

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 the outbreak is now considered to be over.[26] However, transmission continues to occur in the Americas with over 36,000 cases reported in 2022.[27]​ 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.​[28][29][30][31][32][33][34][35]​ Travel-related cases have been declining in US states since 2017, with only 11 travel-associated cases reported in between 2020 and 2022.[36] 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.[37] No travel-related cases have been reported in the UK since 2018.

Although the epidemic has waned, there are continued reports of outbreaks in Asia, India (as recently as late 2021), and Africa.[38] No cases of microcephaly or GBS have been linked to the latest outbreak in India as yet.[39] 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.[40]

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.[41] 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.[42] Specifically, the prevalence rate of congenital microcephaly was reported to be 3%, central nervous system abnormalities were 6%, and intracranial calcifications and ventriculomegaly were 1%.[43]

Data from the US Zika Pregnancy and Infant Registry (which includes US states and territories) between 2015 and 2018 found that approximately 5% of infants born to women with probable or confirmed infection had any Zika-associated brain or eye defect. Around 35% of infants with a birth defect had more than one defect. Analysis of the subgroup with confirmed infection during pregnancy found that approximately 6% of infants had any Zika-associated brain or eye defect. Among pregnancies with confirmed infection, the frequency of any Zika-associated birth defect was higher among those with first (8%) and second (6%) trimester infections compared with third trimester infections (3.8%).[44]

An association between Zika virus infection and GBS was first reported in the outbreak in the Americas in July 2015. Evidence suggests the incidence of GBS to be 24 cases per 100,000 persons infected with Zika.[45] Recovery is variable; some patients return to health while others have chronic disability.[46]

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