Abstract
Summary
Horses from many of the Western States and from Massachusetts have antibodies, in varying proportion, to the St. Louis encephalitis virus. Inoculation in non-immune horses by the subcutaneous, intranasal or intracerebral routes, of a St. Louis virus freshly isolated from mosquitoes, failed to produce clinical disease. It did produce inapparent infection resulting in the presence of virus in the blood, in 2 instances in which suitable tests were made, and in all 4 inoculated animals induced a high titer of serum antibody. We conclude that in horses, inapparent infection occurs frequently in many widely scattered areas of the United States.
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