Researchers isolated a previously unknown virus, named Thogoto virus, from tick pools collected in September 1960 from cattle in the Thogoto forest near Nairobi, Kenya. The tick pool contained Boophilus decoloratus, Rhipicephalus appendiculatus, R. simus, and R. evertsi. The virus was filterable and ether-sensitive, causing severe illness in experimentally infected infant mice, adult mice, hamsters, and sheep. Serial passages showed the virus could be maintained in hamster brain and spleen tissue. Histopathological examination of infected hamsters revealed neuronal degeneration in the cerebellum and cerebral edema. Serological testing against 75 known arboviruses and several other viruses showed Thogoto virus was antigenically distinct from all tested agents. A serological survey of livestock in East Africa revealed high immunity rates in some populations: 12 of 20 cattle and 15 of 15 sheep from Nakuru showed protective antibodies, while lower rates were found in Marigat and Entebbe livestock. No protective antibodies were detected in 48 human sera tested from the same regions. The findings suggest Thogoto virus is a novel tick-borne pathogen with livestock exposure in specific East African geographic areas.

Key findings

• Thogoto virus is a novel, ether-sensitive tick-borne virus isolated from four Rhipicephalus and Boophilus tick species in Kenya, showing no serological relationship to 75 known arboviruses.
• The virus causes acute neurological disease in laboratory animals, producing cerebellar degeneration and cerebral edema with high mortality in hamsters and infant mice within 2-4 days.
• Serological surveys detected high antibody prevalence in East African livestock (60-100% in some cattle and sheep populations) but no antibodies in human serum samples from the same regions.
• The virus is filterable through 410 nm pores but not 210 nm, and is inactivated by ether treatment, indicating an enveloped viral structure.