Fusion and haemolysis of erythrocytes caused by three togaviruses: Semliki Forest, Sindbis and rubella.

Semliki Forest, Sindbis and rubella viruses can fuse erythrocytes from several different species. Large fusion vesicles consisting of tens to hundreds of red blood cells were seen under optical conditions. For the haemagglutination and cell fusion to occur the adsorption of virus and further incubation had to be carried out at pH 5.8. Haemagglutination took place over a wide temperature range (0 to 40 degrees C) whereas fusion required temperatures between 37 and 42 degrees C. Haemolysis of red blood cells induced by togaviruses also required initial incubation at pH 5.8 to enable attachment of the virus to occur after which the pH of the buffer could be raised to neutrality without inhibiting the haemolysis. The amount of togaviruses and Sendai virus required to fuse red blood cells was about the same [I haemagglutinating unit (HAU)/ml] but different ionic conditions were required for fusion.