Viral genome was detected in brain tissue of all young and aged BALB/c mice, apart from one juvenile mouse in which neither antigen nor lesions were identified ( Figure 2 ). Viral genome loads in brain ranged from 10 5.1 -10 13.1 copies HeV/ 10 12 18S; viral genome was also present in lung tissue of four of the five aged animals and one of the five juvenile animals (Mouse 23, Figure 2 ), albeit at lower levels than seen in brain tissue.