Zika virus

Zika virus zēˈkə [key], single-stranded RNA virus of the genus flavivirus that infects human and primates and causes a disease known as Zika fever or zika. It is primarily transmitted by the bite of a female Aedes mosquito, but an infected pregnant mother may transmit the virus to the fetus, and the virus also may, more rarely, be transmitted through sexual intercourse and bodily fluids.

The symptoms of Zika fever typically include a low-grade fever accompanied by a rash, joint pain, or conjunctivitis; there also may be muscle pain, swelling of the joints in the hands or feet, headache, pain behind the eyes, and vomiting. Roughly three out of four persons infected with the virus, however, show no symptoms. In most cases there are no severe complications and the infected individual recovers fully, but in some outbreaks the disease has been associated with clusters of Guillain-Barré syndrome, in which the body's immune system attacks peripheral nerves, producing progressive muscle weakness that can lead to partial or, in severe cases, near total paralysis and potentially death. If the virus is transmitted to a pregnant woman's fetus it can cause significant damage in some cases to the developing brain, the effects of which are most evident in children born with microcephaly, a birth defect characterized by an unusually small head and brain damage, but a range of other neurological and developmental disorders have been associated with exposure to Zika during pregnancy.

Zika fever is often misdiagnosed dengue fever in areas where dengue fever is common because of similar symptoms. There is no vaccine or treatment for the virus, other than alleviating the symptoms of infection. Like other mosquito-borne infections, prevention focuses on controlling the mosquitoes that spread the virus and avoiding being bitten.

The virus was first isolated from a rhesus monkey from Uganda's Zika Forest in 1947, and was first found in humans in Nigeria in 1954. Outbreaks of the disease initially occurred in tropical Africa and SE Asia, but in 2007 there was an outbreak in the Pacific, on Yap island in the Federated States of Micronesia. In 2013 an outbreak occurred in French Polynesia and the disease then spread to other parts of the Pacific. The virus has been identified since 2015 in a number of South and Central American countries, Mexico, the Caribbean, Florida and S Texas, and India, with the most significant outbreak being that in Brazil in 2015–16, which was associated with a sharp increase in the occurrence of microcephaly. An increase in microcephaly cases also was associated with the 2013 outbreak in French Polynesia.

See D. G. McNeil, Jr., Zika: The Emerging Epidemic (2016).

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