Abstract and Introduction
Zika virus is a mosquitoborne flavivirus that is the focus of an ongoing pandemic and public health emergency. Previously limited to sporadic cases in Africa and Asia, the emergence of Zika virus in Brazil in 2015 heralded rapid spread throughout the Americas. Although most Zika virus infections are characterized by subclinical or mild influenza-like illness, severe manifestations have been described, including Guillain-Barre syndrome in adults and microcephaly in babies born to infected mothers. Neither an effective treatment nor a vaccine is available for Zika virus; therefore, the public health response primarily focuses on preventing infection, particularly in pregnant women. Despite growing knowledge about this virus, questions remain regarding the virus's vectors and reservoirs, pathogenesis, genetic diversity, and potential synergistic effects of co-infection with other circulating viruses. These questions highlight the need for research to optimize surveillance, patient management, and public health intervention in the current Zika virus epidemic.
Zika virus is a flavivirus that was first isolated in 1947 from a febrile rhesus macaque monkey in the Zika Forest of Uganda and later identified in Aedes africanus mosquitoes from the same forest. In 1954, the first 3 cases of human infection were reported in Nigeria. Serosurveillance studies in humans suggest that Zika virus is widespread throughout Africa, Asia, and Oceania (online Technical Appendix Table 1, https://wwwnc.cdc.gov/EID/article/22/7/15-1990-Techapp1.pdf). However, these studies may overestimate the virus's true prevalence, given serologic overlap between Zika virus and related flaviviruses, such as dengue virus (DENV) and West Nile virus (WNV).[3,4]
Historically, symptomatic Zika virus infections were limited to sporadic cases or small clusters of patients (online Technical Appendix Table 2).. This pattern changed in 2007, when the first major outbreak of Zika virus infection occurred in Yap (Federated States of Micronesia), where ≈73% of the population were infected and symptomatic disease developed in ≈18% of infected persons. Since then, Zika virus infection has spread rapidly. Outbreaks have occurred in French Polynesia, Cook Islands, Easter Island, New Caledonia, and, most recently, the Americas, with sporadic exportations to Europe (Figures 1–3; online Technical Appendix Table 2).
Cases of laboratory-confirmed, imported Zika virus infections in the United States, by state, January 1, 2015–February 10, 2016 (10). All cases are imported, with the exception of 2 sexually acquired autochthonous cases (11,12).
All countries and regions reporting laboratory-confirmed autochthonous Zika virus cases, January 1, 2015–February 10, 2016 (online Technical Appendix Table 2, https://wwwnc.cdc.gov/EID/article/22/7/15-1990-Techapp1.pdf). Data represent outbreaks and case reports for all reported autochthonous laboratory-confirmed cases of Zika virus infection, including those reported in the peer-reviewed literature; public health agency Web sites, bulletins, and broadcasts; and media reports for selected dates.
South America, Central America, and Caribbean countries and regions reporting laboratory-confirmed autochthonous Zika virus disease cases during January 1, 2015–February 10, 2016 (online Technical Appendix Table 2, https://wwwnc.cdc.gov/EID/article/22/7/15-1990-Techapp1.pdf). Data represent outbreaks and case reports for all reported autochthonous laboratory-confirmed cases of Zika virus infection in these countries and regions during January 1, 1952–February 10, 2016, including those reported in peer-reviewed literature; public health agency Web sites, bulletins, and broadcasts; and media reports.
Zika virus was first reported in May 2015 in continental South America in Brazil, where ≈440,000–1,300,000 persons have subsequently been infected (as of February 16, 2016). Furthermore, 29 other countries in the Americas have reported autochthonous Zika virus transmission, including Puerto Rico and US Virgin Islands (Figure 3; online Technical Appendix Table 2). Except for 2 sexually acquired cases, Zika virus in the United States, Canada, and Europe has been restricted to travelers from affected areas (Figure 1; online Technical Appendix Table 2); a patient who delivered an infant with microcephaly in Hawaii had spent part of her pregnancy in Brazil.
Given the wealth of new information about Zika virus, we conducted a literature review to summarize the published findings. This review contextualizes the ongoing Zika virus epidemic in the Americas and identifies knowledge gaps that must be addressed to combat Zika virus successfully.
Emerging Infectious Diseases. 2016;22(7):1185-1192. © 2016 Centers for Disease Control and Prevention (CDC)