1.Studies on Sindbis virus, a newly recognized member of the arthropod-transmitted viruses, are described; these include data on its immunological characteristics, distribution in the Nile Valley, vertebrate host range, and transmissibility by arthropods.
2.The virus has been isolated from mosquitoes during three successive summers, and once from a juvenile hooded crow (Corvus corone sardonius).
3.It has been placed by Casals and Brown (1954) in Group A of the arthropod-transmitted viruses, but is distinguishable from other members of this group by the neutralization test.
4.Its particle size, estimated by gradacol membrane filtration, is between 40 and 48 mu.
5.On initial passages by brain-to-brain transfer it is fatal to infant mice but not to adult mice.
6.It is highly fatal to embryonated hens' eggs and is markedly cytopathogenic to outgrowths of fibroblastic cells in chick embryo tissue cultures.
7.Experimentally it is easily transmitted by Culex mosquitoes (Culex pipiens L. and Culex univittatus Theobald), and Ornithodoros savignyi (Audouin) ticks are infectible by parenteral puncture and will subsequently transmit the infection by feeding upon infant mice.
8.Antibody surveys imply a) a wide vertebrate host range including man, domestic quadrupeds, birds, and domestic fowl, and b) frequent human infection (27 per cent), particularly in the age group of 15 years and over (34 per cent), in the Nile Delta, and less frequent human infection (12 per cent) in the Southern Sudan.
9.No information is available on the symptomatology of natural infections.
Present address: The Rockefeller Foundation Virus Laboratories. 66th Street & York Ave., New York 21, New York.