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Understanding Zika Virus
U. S. Center for Disease Control on Zika

Zika virus disease (Zika) is a disease caused by the Zika virus, which is spread to people primarily through the bite of an infected Aedes species mosquito. The most common symptoms of Zika are fever, rash, joint pain, and conjunctivitis (red eyes). The illness is usually mild with symptoms lasting for several days to a week after being bitten by an infected mosquito. People usually don’t get sick enough to go to the hospital, and they very rarely die of Zika. For this reason, many people might not realize they have been infected. However, Zika virus infection during pregnancy can cause a serious birth defect called microcephaly(, as well as other severe fetal brain defects. Once a person has been infected, he or she is likely to be protected from future infections.

Zika virus was first discovered in 1947 and is named after the Zika Forest in Uganda. In 1952, the first human cases of Zika were detected and since then, outbreaks of Zika have been reported in tropical Africa, Southeast Asia, and the Pacific Islands. Zika outbreaks have probably occurred in many locations. Before 2007, at least 14 cases of Zika had been documented, although other cases were likely to have occurred and were not reported. Because the symptoms of Zika are similar to those of many other diseases, many cases may not have been recognized.

On January 22, 2016, CDC activated its Incident Management System and, working through the Emergency Operations Center (EOC), centralized its response to the outbreaks of Zika occurring in the Americas and increased reports of birth defects and Guillain-Barré syndrome in areas affected by Zika. On February 1, 2016, the World Health Organization declared a Public Health Emergency of International Concern (PHEIC) because of clusters of microcephaly and other neurological disorders in some areas affected by Zika. On February 8, 2016, CDC elevated its response efforts to a Level 1 activation, the highest response level at the agency.

CDC is working with international public health partners and with state and local health departments to:
  • Alert healthcare providers and the public about Zika.
  • Post travel notices and other travel-related guidance.
  • Provide state health laboratories with diagnostic tests.
  • Monitor and report cases of Zika, which will help improve our understanding of how and where Zika is spreading.

US States

  • No local mosquito-borne Zika virus disease cases have been reported in US states, but there have been travel-associated cases.
  • With the recent outbreaks, the number of Zika cases among travelers visiting or returning to the United States will likely increase.
  • These imported cases could result in local spread of the virus in some areas of the United States.

See also the attached, Understanding Zika, for more information on the Zika Virus and the vector mosquitoes associated with Zika.