Zika Virus

Abstract

I n 1947, a study of yellow fever yielded the first isolation of a new virus, from the blood of a sentinel rhesus macaque that had been placed in the Zika Forest of Uganda. 1 Zika virus remained in relative obscurity for nearly 70 years; then, within the span of just 1 year, Zika virus was introduced into Brazil from the Pacific Islands and spread rapidly throughout the Americas.2 It became the first major infectious disease linked to human birth defects to be discovered in more than half a century and created such global alarm that the World Health Organization (WHO) would declare a Public Health Emergency of International Concern. 3 This review describes the current understanding of the epidemiology, transmission, clinical characteristics, and diagnosis of Zika virus infection, as well as the future outlook with regard to this disease. Epidemiol ogyZika virus is a flavivirus, in the family Flaviviridae.Although Zika virus was isolated on several occasions from Aedes africanus mosquitoes after its discovery in 1947, 4 there initially was no indication that the virus caused human disease.Nevertheless, a serosurvey involving residents of multiple areas of Uganda revealed a 6.1% seroprevalence of antibodies against Zika virus, which suggested that human infection was frequent.5 Additional serosurveys indicated a much broader geographic distribution of human infection, including Egypt, 6 East Africa, 7 Nigeria, 8 India, 9 Thailand, 10 Vietnam, 10 the Philippines, 11 and Malaysia (near Kuala Lumpur and in East Malaysia [Sabah and Federal Territory of Labuan]).12 Human illness caused by Zika virus was first recognized in Nigeria in 1953, when viral infection was confirmed in three ill persons.8 Despite recognition that Zika virus infection could produce a mild, febrile illness, only 13 naturally acquired cases were reported during the next 57 years.[13][14][15][16] Thus, it came as a great surprise when a 2007 outbreak on several islands in the State of Yap, Federated States of Micronesia, resulted in an estimated 5000 infections among the total population of 6700.17 Subsequently, an outbreak in French Polynesia in 2013 and 2014 is estimated to have involved 32,000 persons who underwent evaluation for suspected Zika virus infection.[18][19][20] Although most of the illnesses appeared similar to those seen in Yap, cases of Guillain-Barré syndrome were also noted.19,21 Subsequent outbreaks occurred on other Pacific islands, including New Caledonia (in 2014), 22 Easter Island (2014), 23 Cook Islands (2014), 24 Samoa (2015), and American Samoa (2016) (Fig. 1).In stark contrast to these outbreaks, in the past 6 years, only sporadic cases of Zika virus infection have been reported in Thailand, 25,26 East Malaysia (Sabah), 27 Cambodia, 28 the Philippines, 29 and Indonesia.30,31 Zika virus was first identified in the Americas in March 2015, when an outbreak