The virus is primarily transmitted by midge bites and affects cattle, goats, sheep and camelids such as llamas, and midges are most active between April and November.
Mae'r feirws yn cael ei drosglwyddo'n bennaf gan bigiadau gwybed ac mae'n effeithio ar wartheg, geifr, defaid a chamelod fel lamas, ac mae gwybed yn fwyaf amlwg rhwng Ebrill a Thachwedd.