A relatively newly recognised cause of congenital infection when acquired by a woman in the early stages of pregnancy. The virus has been known in Africa and Asia since the 1940s but it has spread widely in the last 10 years to the Americas, western Pacific and to more African countries. It is transmitted by the mosquito Aedes aegypti. Although the large majority of infected persons have no or minor symptoms, in 2013 it was found to cause GUILLAIN-BARRÉ SYNDROME in some patients in French Polynesia; an epidemic in South America, starting in in 2016, has been associated with MICROCEPHALY in affected foetuses with malformation of the underlying cerebral cortex and/or cerebellum and with arthrogryposis. This led the World Health Organisation to declare a public health emergency. There is no specific anti-viral treatment so the major requirement is to control spread of the mosquito vector. Pregnant women are advised to take precautions against mosquito bites and not to travel to affected areas. Because the virus can also be transmitted by sexual contact, those at risk are advised to take whatever contraceptive precautions they regard as ethically or morally acceptable.