A mosquito-borne flavivirus that usually causes mild symptoms in humans, including fever, skin rashes, conjunctivitis, muscle and joint pain, malaise, and headache. However, infection during pregnancy can result in brain abnormalities of the fetus, notably microcephaly (an abnormally small skull). Zika virus can also trigger Guillain–Barré syndrome—a more severe disease of the peripheral nerves, possibly causing breathing difficulties. Infection is usually from a mosquito bite, although the virus may also be transmitted by sexual intercourse. The virus was first isolated in a rhesus monkey in the Zika forest of Uganda in 1947.