EVALUATION OF VASCULAR CLEARANCE AS A MARKER FOR VIRULENCE OF ALPHA-VIRUSES - DISASSOCIATION OF RAPID CLEARANCE WITH LOW VIRULENCE OF VENEZUELAN ENCEPHALITIS-VIRUS STRAINS IN GUINEA-PIGS

The concept that relates low virulence of certain alphaviruses to low viremia and efficient vascular clearance of virus was tested in guinea pigs. Previously published studies with hamsters suggested that virulent strains maintain high viremias primarily because they are cleared inefficiently from the blood. In guinea pigs, 6 of 6 virulent strains of Venezuelan encephalitis virus were cleared inefficiently, whereas 3 of 6 nonlethal or benign virus strains were cleared rapidly. However, 3 other guinea pig-benign Venezuelan encephalitis virus strains cleared slowly, like lethal strains. The inability of 1 benign virus strain, which cleared slowly, to produce a high viremia was correlated with inefficient growth in primary viral replication sites. Thus, the potential of some alphaviruses to produce destructive lesions may be restricted by efficient clearance of virus from the blood, whereas the growth of other benign alphavirus strains may be restricted after the virus is presented to target cells.