YM 50/64 a new arbovirus prototype designed as Okola virus has been isolated from a pool of 15 Eretmapodites gr. chrysogaster captured in 1964, at 25 km from Yaounde (Federal Republic of Cameroons).
Okola virus showed physical and chemical properties of an arbovirus. It was difficult to obtain its hemagglutinating antigen. This strain proved to be serologically different from all african arbovirus to which it was compared by complemenr fixation and neutralisation tests both at the East African Virus Research Institute (Entebbe) and the Pasteur Institute (Dakar). It is therefore temporarily classed in the non grouped mosquitoe born viruses.
A very low percentage of the inhabitants of Cameroons possessed hemagglurination-inhibition antibodies, except in the north of the country.