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  • Most infected persons asymptomatically seroconvert.

  • Clinical symptoms are akin to those of chikungunya virus infection but with less arthritis.

  • Complications include microcephaly and ocular complications in infants born to mothers infected during pregnancy as well as Guillain-Barré.

  • There is no effective antiviral or vaccine.

General Considerations

Zika virus is a flavivirus, akin to the viruses that cause dengue fever, Japanese encephalitis, and West Nile infection. It was originally isolated from macaques in 1947, in the Zika forest near the Entebbe airport of Uganda. The virus was named Zika in 1952, and the first human cases were noted in Nigeria in 1968 although earlier cases probably occurred in Uganda and Tanzania.

The virus was noted in Africa and Asia during the 1950s–1980s, but first spread beyond those two continents during 2007 when an outbreak occurred in Yap State, Federated States of Micronesia. A large outbreak occurred in French Polynesia in 2013. A smaller outbreak occurred on Easter Island during 2014. The virus then spread to the Western hemisphere and was first noted in northeastern Brazil in 2015. Up to 1.3 million cases occurred in Brazil during that year. Zika virus then spread rapidly throughout the Americas, including the United States and worldwide Global WHO reports show that transmission is ongoing in 79 nations, interrupted in 5, and potential with presence of vectors in 64. Despite distinct lineages, Zika virus exists as only one serotype.

Aedes species mosquitoes, particularly Aedes aegypti, are primarily responsible for transmission of Zika virus. The biodistribution of the species largely determines the area of prevalence for Zika virus. Aedes species mosquitoes are found primarily in the southeastern United States, but one species Aedes albopictus (the Asian tiger mosquito known to sequester in tires) may be seen as far north as Pennsylvania and New Jersey. Rarely, a few other mosquito species including Anopheles and Culex may be competent for the Zika virus. Sexual transmission is reported from males and females to partners via vaginal, anal, or oral sex. Vertical transmission from pregnant woman to fetus is prominent. Transmission via platelet transfusion is also reported.

Since the onset of the first reported cases in the United States in 2015, the number of reported Zika cases is over 43,000, with 37,286 symptomatic cases from US territories (largely Puerto Rico) and 5728 cases from US states. The territorial cases are largely locally acquired and the US state cases are largely travel-acquired (with 231 of the 5728 US cases acquired via local transmission and 55 via sexual, bloodborne, or unknown routes). As of October 31, 2018, the US states reported 45 cases, with California (12) and New York (8) having the highest numbers. The number of annual cases is diminishing markedly in the United States with a peak in 2016 of 4897 travel-associated cases and 224 locally acquired ...

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