This is a transmission electron micrograph (TEM) of Zika virus, which is a member of the family Flaviviridae. Virus particles are 40 nm in diameter, with an outer envelope, and an inner dense core. (credit: CDC) Two months after a 68-year old British man became sick with Zika virus, traces of the germ lingered in his semen, researchers reported Friday. The finding suggests that the mosquito-spread virus may unexpectedly hang around in the body for much longer than symptoms appear, which typically only last for about a week.