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1. ZIKA VIRUS

ESSENTIALS OF DIAGNOSIS

  • Most infected persons asymptomatically seroconvert.

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

  • Complications include microcephaly and ocular abnormalities 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, and 239,742 cases were subsequently reported between 2015 and 2018. Zika virus spread rapidly throughout the Americas, including the United States and worldwide (http://www.who.int/csr/disease/zika/en/). Autochthonous transmission of Zika virus has been reported in 87 countries and territories. In October, 2019, the first mosquito-transmitted, locally acquired cases of Zika virus were reported in Europe (Southern France). 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 most cases from US territories (largely Puerto Rico). The territorial cases are largely locally acquired and the US state cases are largely travel-acquired. 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 cases (Florida, 218; Texas, 6). As of November 7, 2019, there have been 15 cases (14 in travelers and 1 laboratory-acquired case) in the US states and 51 (49 locally acquired cases and 2 travel-associated cases) in the US territories.

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