Some characteristics of four attenuated vaccine virus strains and a virulent strain of Aujeszky's disease virus

In the present study four attenuated virus strains, used as vaccines, and a virulent strain of Aujeszky's disease virus (ADV) were compared with respect to their virulence in mice, their ability to induce virus-specified thymidine kinase (TK) in infected cells, and their cleavage profiles of viral DNA's after treatment with the restriction endonuclease KpnI. The survival time of mice inoculated with the B-KAL or the virulent NIA-3 strain was comparable, whereas the Bartha and BUK strains required significantly longer periods to kill mice. Mice were resistant to the MK-25 strain of ADV. The strains were assayed for TK phenotype by plaque autoradiography after 3H-thymidine labelling of infected cells. MK-25 proved to be the only strain defective in induction of TK in pig kidney cells. Restriction endonuclease analysis of viral DNA's revealed that each vaccine strain showed a characteristic fragment pattern that could easily be differentiated from that of other vaccine and field strains of ADV. The present results demonstrate that the mouse virulence test and the TK assay detect differences in biological properties of ADV strains, but that restriction endonuclease analysis is required for unambiguous identification of vaccine and field strains of ADV.     

Effect of infections with swine fever virus on immune functions I. Response of lymphocytes from blood and lymphoid organs from infected and normal pigs to anti-immunoglobulin serum and protein A

Pigs exposed to a low-virulent strain of swine fever virus (SFV) developed an inapparent infection. At times when a transient leucopenia occurred, the peripheral blood lymphocytes (PBL) were unresponsive to the mitogenic stimulus of anti-immunoglobulin serum (anti-Ig) and protein A.Pigs lethally infected with a virulent SFV showed leucopenia and unresponsiveness of PBL to anti-Ig and protein A from 2 days post infection until death.This suggests a defect in B lymphocyte function in pigs infected with SFV. The unresponsiveness to anti-Ig appeared not to be caused by a reduced ability of lymphocytes to redistribute their receptors into caps, the presence of suppressor cells or absence of surface immunoglobulin bearing lymphocytes in the peripheral blood. A direct action of the virus itself also seemed unlikely.Lymphocytes from spleen reacted as PBL. However, lymph node cells did not lose their capability to respond to anti-Ig.These data suggest that a change in the migration pattern of anti-Ig responsive lymphocytes could account for the observed unresponsiveness of PBL and spleen lymphocytes to anti-Ig.     

Pseudorabies virus is transmitted among vaccinated conventional pigs, but not among vaccinated SPF pigs

Whereas the reproduction ratio (R) of pseudorabies virus (PRV) in vaccinated specific pathogen free (SPF) pigs without maternally derived antibodies under experimental conditions has repeatedly been shown to be significantly below 1, R in vaccinated conventional pigs in the field with maternally derived antibodies was significantly above 1. To exclude the difference in husbandry conditions as a cause for this discrepancy, we quantified and compared the transmission of PRV in both groups under identical experimental conditions. Whereas none of the SPF sentinel pigs became infected (R=0, significantly<1), all conventional sentinel pigs did become infected (R=2.5, significantly>1). Moreover, only one SPF pigs shed virus in saliva, the mean cumulative titre being almost a 100-fold less than in conventional pigs (17 pigs, P=0.003). In addition, the mean proliferation of peripheral blood lymphocytes in response to PRV antigens was significantly higher in SPF pigs than in conventional pigs at all points studied (P<0.0001). Moreover, the virus-neutralising antibody titre after vaccination was significantly higher in SPF pigs than in conventional pigs. We conclude that the discrepancy in transmission between vaccinated SPF pigs and vaccinated conventional pigs cannot be attributed to the experimental conditions.     

Airborne transmission of BHV1, BRSV, and BVDV among cattle is possible under experimental conditions

To control the diseases caused by bovine herpesvirus 1 (BHV1), bovine respiratory syncytial virus (BRSV), and bovine virus diarrhoea virus (BVDV), it is crucial to know their modes of transmission. The purpose of this study was to determine whether these viruses can be transmitted by air to a substantial extent. Calves were housed in two separate isolation stables in which a unidirectional airflow was maintained through a tube in the wall. In one stable, three of the five calves were experimentally infected with BHV1 and later with BRSV. In the BVDV experiment, two calves persistently infected with BVDV (PI-calves) instead of experimentally infected calves, were used as the source of the virus. In all the calves infections were monitored using virus and antibody detection. Results showed that all the three viruses were transmitted by air. BHV1 spread to sentinel calves in the adjacent stable within three days, and BRSV within nine days, and BVDV spread to sentinel calves probably within one week. Although airborne transmission is possibly not the main route of transmission, these findings will have consequences for disease prevention and regulations in control programmes.     

Effect of Roscovitine‐Treated Donor Cells on Development of Porcine Cloned Embryos

Synchronization of the donor cell cycle is an important factor for successful animal cloning by nuclear transfer. To improve the efficiency of porcine cloning, in the present report, we evaluated effects of contact inhibition, serum starvation and roscovitine treatment of donor cells on in vitro and in vivo developmental potency of cloned porcine embryos. Fibroblasts derived from a porcine foetus at day 30 of gestation were isolated and cultured to 70% confluency. Then, cells were either cultured to 100% confluency for contact inhibition, or cultured in 0.5% serum for 72 h for serum starvation or with 15 μm roscovitine for 24 h. Cells were most effectively synchronized at G0/G1 in the serum starvation group (87.5%) compared with the contact inhibition and roscovitine treatment groups (76.3% and 79.9% respectively p < 0.05). However, after somatic cell nuclear transfer followed by in vitro culture, the serum starvation group showed a significantly lower blastocyst formation rate (5.6%) compared with the contact inhibition and roscovitine treatment groups (11.6% and 20.0% respectively). Differential expression of apoptosis‐related genes and the level of apoptosis in each treatment group explain the variation in developmental competence among the groups. Significantly higher level of apoptosis was observed in the serum starvation group. On the other hand, the roscovitine treatment group shows the lowest level of apoptosis and the best in vitro development among the groups. Cloned embryos derived from roscovitine‐treated donor cells were transferred to surrogate pigs. Three healthy live piglets were produced. In conclusion, we suggest that roscovitine treatment of donor cells improves development of cloned porcine embryos and can raise the efficiency of cloned piglet production.     

Therapeutic efficacy of zeta-cypermethrin pour-on for the treatment of biting and sucking lice in cattle under field conditions

OBJECTIVE: To assess the efficacy of zeta-cypermethrin pour-on to control cattle lice. DESIGN: Five field trials in south-eastern Australia. PROCEDURE: Zeta-cypermethrin pour-on, deltamethrin pour-on and pour-on vehicle were applied to groups of 10 cattle. Lice were counted before treatment and 14, 28, 42 and 56 days after treatment. RESULTS: Zeta-cypermethrin pour-on given at 2.5 mg/kg was equivalent to, or marginally more effective than a deltamethrin pour-on at 0.75 mg/kg. It eliminated B bovis and H eurysternus and gave good control of L vituli and S capillatus. Zeta-cypermethrin at 1 mg/kg gave good control of B bovis and H eurysternus but was not satisfactory against L vituli and S capillatus. CONCLUSION: Zeta-cypermethrin pour-on, given at 2.5 mg/kg, is an effective treatment for cattle lice control. Zeta-cypermethrin, and other synthetic pyrethroid pour-ons, are the treatment of choice to control B bovis.