A novel virus, designated swine hepatitis E virus (swine HEV), was identified in pigs. Swine HEV crossreacts with antibody to the human HEV capsid antigen. Swine HEV is a ubiquitous agent and the majority of swine >3 months of age in herds from the midwestern United States were seropositive. Young pigs naturally infected by swine HEV were clinically normal but had microscopic evidence of hepatitis, and developed viremia prior to seroconversion. The entire ORFs 2 and 3 were amplified by reverse transcription-PCR from sera of naturally infected pigs. The putative capsid gene (ORF2) of swine HEV shared about 79-80% sequence identity at the nucleotide level and 90-92% identity at the amino acid level with human HEV strains. The small ORF3 of swine HEV had 83-85% nucleotide sequence identity and 77-82% amino acid identity with human HEV strains. Phylogenetic analyses showed that swine HEV is closely related to, but distinct from, human HEV strains. The discovery of swine HEV not only has implications for HEV vaccine development, diagnosis, and biology, but also raises a potential public health concern for zoonosis or xenozoonosis following xenotransplantation with pig organs.

The forward masking of a sinusoidal signal by a sinusoid of the same frequency was investigated for frequencies ranging from 125 to 4000 Hz. Forward masking in dB is proportional to both masker level and log signal delay at each frequency. More forward masking occurs at very low frequencies than at high frequencies, given equal-sensation-level maskers, and masked thresholds are greater at low frequencies than at high frequencies given equal-SPL maskers. The data can be described equally well by assuming that the difference in forward masking as a function of frequency is due to a change in the time course of recovery from masking or to a change in the growth of masking at each signal delay. The frequency effect is not large enough to change the interpretation of forward-masking data in studies of suppression or psychophysical tuning curves.