Morphology of the GB hepatitis agent

ATTEMPTS to isolate hepatitis A virus have been in progress for several decades. An important advance was the finding that the marmoset served as a permissive animal host for this virus1, but it became obvious that more than one agent was active. The pedigree of one agent was established as MS-1 (hepatitis A) isolate, while the other, which was demonstrably different by neutralisation and cross-challenge experiments, was designated GB. The GB infectious serum was obtained on the third day of jaundice from a surgeon in Chicago who developed a mild form of acute hepatitis. This serum induced hepatitis in all four marmosets inoculated. A pool of infectious GB serum marmoset (passage 11) was prepared from the total bleeding of nine white-lipped marmosets (Saguinus sp.) 19–24 d after inoculation and during the early acute phase of hepatitis as indicated by an increase of serum transaminase levels. This pool, designated H 205 GB pass 11, has an infectivity of 104.5 marmoset ID50. We have now examined the GB agent electron microscopically, and found that it is smaller and more fragile than the MS-1 strain2, and therefore also the identical CR326 isolate3 of hepatitis A, which have the morphological appearances of recognised, small cubic viruses measuring about 27 nm in diameter.