Wesselsbron (WSL) virus is an arthropod-borne virus in the genus Flavivirus of the family Flaviviridae[1] that causes Wesselsbron disease in cattle, sheep, goats, camels, pigs, donkeys, horses, ostriches, and wild ruminants[2] with occasional incidental spillover to humans.

The first known outbreak was reported in 1955 on a sheep farm in the town of Wesselsbrons in Orange Free State Province, South Africa after an increase of lamb deaths and ewe abortions.

[7] Since 1955, WSL virus has been found in animals and mosquitos from Zimbabwe, Uganda, Kenya, Nigeria, Central African Republic, Senegal, Cameroon, and Ivory Coast.

Signs of illness, which include but are not limited to fever, anorexia, listlessness, weakness, and increased respiration, can often go undetected because they are not specific to any disease.

The WSL virus has an incubation period of 2–4 days[13] before leading to a sudden onset of a generally mild, acute phase that includes fever, rigors, headache, myalgia, arthralgia, and impaired vision.