A novel virus in swine is closely related to the human hepatitis E virus.

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.

Field trial to evaluate immunogenicity of a glycoprotein I (gE)-deleted pseudorabies virus vaccine after its administration in the presence of maternal antibodies.

A field trial was conducted on a commercial swine farm quarantined because of infection with pseudorabies virus. The purpose was to investigate, in growing pigs born to hyperimmunized sows, the immunogenicity of a vaccine with a glycoprotein I (gE) deletion. One hundred twenty pigs were assigned at random to 1 of 3 vaccination schedules at ages: 8 and 12 weeks; 8, 12, and 14 weeks; and 8, 12, and 16 weeks. Immune response was measured at 8, 12, 14, 16, and 18 weeks, using the serum neutralization test, a screening ELISA, and assays of IgG and IgA in serum and nasal secretions. Results of the serum neutralization test and the screening ELISA indicated that, for pigs vaccinated only at 8 and 12 weeks, the percentage of pigs with pseudorabies virus serum antibodies decreased substantially by 18 weeks; for pigs given a booster at 14 or 16 weeks, the prevalence of serum antibodies at 18 weeks was higher, with 16-week booster vaccination eliciting the best response. At each age, nasal IgA and IgG values were highly correlated (r > or = 0.70), as were serum IgA and IgG values; correlations of serum with nasal IgA and IgG values were somewhat lower (approx range, r = 0.40 to 0.70). Nevertheless, an increase in serum IgA or IgG values on vaccination was no guarantee of an increase in nasal IgA or IgG values. For serum and nasal mucosal antibodies, a poor immune response was associated with high quantities of maternally derived antibodies. Vaccination at 16 weeks was necessary to ensure eliciting of an immune response in almost all pigs.

Eradication of pseudorabies virus from three large swine herds achieved by management intervention and use of a vaccine with a deletion for glycoprotein I.

Three large farrow-to-finish swine herds in Illinois, quarantined because of infection with pseudorabies virus (PRV), were enrolled in an intensified PRV eradication program, with the goal being release from quarantine within 3 years. The intervention plan primarily relied on vaccination, using a vaccine with a deletion of the genes coding for glycoprotein I, in breeding and growing/finishing pigs and decreases of movement and mixing of growing/finishing pigs. The initial goal was to decrease viral spread in the growing/finishing pigs, thereby enabling production of seronegative replacement gilts. Off-site rearing of replacement gilts was implemented in 1 recently infected herd in which the seroprevalence in the growing/finishing group was high. Results of bimonthly serologic monitoring indicated that there was minimal spread of PRV in the growing/finishing pigs after 1 year. Increases in the number of sows culled combined with an increase in the number of seronegative replacement gilts entering the breeding group resulted in a reduction of sow seroprevalence, so that phased test and removal of seropositive breeding stock could commence in all 3 herds at about 18 months after initiation of the program. Persistent use of the test-and-removal procedure and repeated testing for release from quarantine were required for the most recently infected herd. All herds were released from quarantine within 3 years, indicating that a PRV eradication program based on vaccination and management changes designed to minimize the spread of PRV can be used in conjunction with test-and-removal procedures to effectively eliminate PRV from large farrow-to-finish swine herds.

Progress after one year of a pseudorabies eradication program for large swine herds.

Six large farrow-to-finish swine herds quarantined for pseudorabies in Illinois participated in the USDA-initiated Large Herd Cleanup Study. These herds were monitored for antibodies to pseudorabies virus (PRV) for 1 year after the initiation of an intensive eradication program. Herd size ranged between 425 and 1,500 females of breeding age. Gene-deleted modified-live virus vaccines were used on all farms, with 3 of the 6 herds receiving a vaccine with a deletion of the gene for glycoprotein-I and the other 3 herds receiving a vaccine with a deletion of the gene for glycoprotein-X. The breeding herd and growing pigs were vaccinated on each farm. Each herd produced its own replacement gilts. In addition, management changes emphasizing all-in, all-out pig flow were initiated. One year after initiation of the vaccination program, sera for the measurement of PRV antibodies were obtained from sows and heavy finishing pigs (> 70 kg) from each of the farms. Prevalence of PRV antibodies attributable to wild-type virus infection ranged from 7 to 63% (median, 33%) for sows and from 0 to 42% (median, 4%) for finishers, as determined by the appropriate vaccine differential test. For each sow herd, there was a large decrease in the PRV seroprevalence rate after 1 year of the program (range, -21 to -68%; median, -42%). Examination of PRV prevalence rates by parity indicated decreased seroprevalences in the lower parities (< 2) in 3 of the herds, suggesting that vaccination reduced the spread of PRV.(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of the sensitivity and specificity of two diagnostic tests for antibodies to pseudorabies virus glycoprotein X.

The diagnostic performance of 2 enzyme-linked immunosorbent assays (gX-T, gX-H) for antibodies to pseudorabies virus (PRV) glycoprotein X (gX) were evaluated using 311 serum samples from a nonvaccinated quarantined herd. When the standardized virus neutralization (VN) test, which uses the Shope strain (VN Shope), was used as the comparative diagnostic standard, the gX-T test had a 7% false-negative rate and a 52% false-positive rate, and the gX-H test had a 19% false-negative rate and a 19% false-positive rate. When the VN test with a Bartha recombinant strain (VN Bartha gIIIKa) was used as the diagnostic standard, the gX-T test had a 9% false-negative rate and a 26% false-positive rate, and the gX-H test had a 24% false-negative rate and a 11% false-positive rate. Thus, the gX-T test was more sensitive and the gX-H test was more specific. Additional diagnostic tests on 79 serum samples from a noninfected herd did not produce false positives for the gX-H test, but there was an 8% false-positive rate for the gX-T test. Previous studies from our laboratory have demonstrated that VN Bartha gIIIKa has higher sensitivity than VN Shope, without losing specificity, and thus is a better comparative diagnostic standard. When adding a suspect range to the gX-T test, using the same criteria as the suspect range for the gX-H test, the false-positive rate of the gX-T test was reduced to 5% when evaluated versus VN Bartha gIIIKa in the infected herd and to 1% for the PRV-negative herd.(ABSTRACT TRUNCATED AT 250 WORDS)

Prevalence of pseudorabies virus infection and associated infections in six large swine herds in Illinois.

Sera were collected from 6 large farrow-to-finish swine herds infected with pseudorabies virus (PRV) in Illinois. All herds were participating in the Large Herd Cleanup Study, a USDA-initiated project to evaluate the feasibility of eradicating pseudorabies from large farms (greater than 400 sows) by use of a combination of vaccination and management changes. Herd size ranged between 425 and 1,500 breeding females. Between April and July 1990, sera for measurement of PRV antibodies were obtained from 113 to 156 sows and 112 to 162 finishing pigs (body weight greater than 70 kg)/herd. Duplicate sera from 30 sows and 30 market-weight pigs/herd were obtained for measurement of serum antibodies to the following associated organisms: swine influenza virus, transmissible gastroenteritis virus, encephalomyocarditis virus, Actinobacillus pleuropneumoniae, Eperythrozoon suis, and 6 serovars of Leptospira interrogans. Prevalence of PRV antibodies attributable to field virus infection ranged between 53.8 and 100% for sows and between 0.7 and 97.3% for finishing pigs, as determined by the appropriate differential test for the vaccine being used on each farm. In only 1 herd, PRV seroprevalence was increased with higher sow parity. For associated infections, the risk of seropositivity attributable to PRV was not significant (for most infections) on all farms and varied among farms. Thus, pseudorabies did not appear, in general, to increase susceptibility to infection with other disease agents.

Responses to copulatory stimulation in neonatally androgenized female rats.

A series of experiments evaluated the extent to which copulatory stimulation could ameliorate the anestrus and sterility exhibited by neonatally androgenized female rats. The age at which animals began to exhibit persistent vaginal estrus and the degree of sexual receptivity exhibited under several testing paradigms were found to be inversely related to the dose of testosterone propionate (TP) injected neonatally. With increasing numbers of mounts received, both the number of androgenized animals exhibiting sexual receptivity and the quality of the estrous behavior exhibited tended to increase. The extent to which copulatory stimulation modified receptivity varied with the dose of TP injected neonatally and the condition of testing. Animals injected with high doses of TP (500 microgram) usually showed little or no receptive behavior even in the most extensive behavioral tests. However, under some testing conditions animals receiving 50 micrograms of TP neonatally, while showing little or no receptivity during initial mounts, showed increased receptivity as behavioral tests were extended. Following matings that included one to five ejaculations, only control animals were observed to become pregnant. However, when androgenized females cohabited with males for an extended period, animals that had neonatally received .5 microgram of TP, but not higher doses, did become pregnant. It is concluded that the capacity of systems mediating reproductive physiology and behavior to be facilitated by stimuli associated with males and that mating is a characteristic of the female rat which can be manipulated by injection of hormones during the neonatal period.

Forward masking as a function of frequency, masker level, and signal delay.

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.