Enhanced Resistance of Mice to Infection with Langat (TP21) Virus Following Pre-treatment with Sindbis or Semliki Forest Virus

The Rayne Institute, St Thomas' Hospital, London, SE1 and * Microbiological Research Establishment, Porton Down, nr. Salisbury, Wilts., U.K. Significant protection to heterologous i.c. challenge with the flavovirus Langat occurred after a single i.c. injection of avirulent strains of the alpha viruses Semliki Forest or Sindbis given 1 day to 5 weeks before challenge. Some protection also occurred after an i.p. infection with these viruses. We consider that the protection afforded by the alpha viruses is due to interference with the multiplication of Langat virus and is related to the maximum level of brain infectivity reached in the alpha virus infection. Received 7 April 1976; accepted 16 June 1976.