The use of a whole inactivated PRRS virus vaccine administered in sows and impact on maternally derived immunity and timing of PRRS virus infection in piglets.

Background: Porcine reproductive and respiratory syndrome virus (PRRSV) vaccination is usually based on administering periodically PRRS modified live virus (MLV) in sows throughout their life. Using this schedule, transfer of maternally derived antibodies to the offspring is limited. The aim of the present study was to test the concept of priming with an MLV and boosting with a commercial inactivated virus vaccine in sows to reduce PRRSV incidence and improve productivity. Methods: On two farms, all the sows were vaccinated with a MLV vaccine at week 8 of gestation. Then two groups were designated, one group was re-vaccinated in the third week prior to farrowing and using a commercial inactivated vaccine (the PG group). The second group was the control group (C). Assays for PRRSV infection and productive parameters were evaluated. Results: For both farms, the incidence of PRRSV was lower at 6 weeks of age in PG than in C (p < 0.05). At weaning the proportion of PRRSV seropositive piglets was higher for PG as well (p < 0.05). The litters from C sows from both farms showed a higher pre-weaning mortality (odds ratio, C vs. PG = 1.18 ± 0.09; p < 0.05). Conclusions: Administration of the vaccine in sows before farrowing was safe and associated with reduced incidence of PRRSV in piglets up to 6 weeks of age.

Classical swine fever: comparison of oronasal immunisation with CP7E2alf marker and C-strain vaccines in domestic pigs.

Effective oronasal vaccination against classical swine fever (CSF) is essential to achieve protection in wild boar. However the currently available live CSF vaccines, e.g. C-strain, do not allow serological differentiation between infected and vaccinated animals (DIVA). A modified live marker vaccine candidate (CP7E2alf) has been recently developed (Reimann et al., 2004). This communication reports the comparison of CP7E2alf and C-strain virus vaccines during 98 days following oronasal immunisation in domestic pigs. C-strain vaccine virus was consistently detected in tonsils of all (n=30) animals from 3 to 77 days post vaccination (dpv) and in blood (n=36) between 3 and 13dpv by CSFV-specific rRT-PCR. CP7E2alf virus RNA was detected in 6 animals slaughtered between 4 and 63dpv by a BVDV-specific rRT-PCR. The chimeric virus was not detected in blood samples. As detected by CSFV E2-specific antibody ELISA and virus neutralisation tests, seroconversion first occurred at 11dpv in the C-strain vaccinated group and between 11 and 15dpv in the CP7E2alf vaccinated group. The serological response was still present at 98dpv. The CP7E2alf serological response remained negative using the CSFV E(rns) ELISA whereas seroconversion occurred in the C-strain vaccinated group. In conclusion, the primary replication site of CP7E2alf vaccine virus was found to be the tonsils as in the C-strain and virulent field strains. Persistence of CP7E2alf in the tonsils was also demonstrated up to 63dpv. Both vaccines showed immunogenicity after oronasal administration in domestic pigs. In contrast to the C-strain, CP7E2alf vaccine allowed the use of DIVA approaches in serological tests. This study confirms CP7E2alf as a promising marker vaccine candidate for oronasal vaccination programmes to control CSF in domestic pigs and wild boar.

Occurrence of atypical myxomatosis in Central Europe: clinical and virological examinations.

An outbreak of the atypical form of myxomatosis struck a rabbit farm in Hungary. The animals had previously been vaccinated with a vaccine containing Shope rabbit fibroma virus strain. The disease appeared in winter when the presence of mosquitoes and fleas is not common. The virus was isolated from an eyelid specimen of a naturally infected rabbit. The surviving animals were observed for four weeks, blood samples were collected and, after euthanasia, organ specimens were also examined by morphological methods including pathology and electron microscopy. Serum samples were examined by virus neutralisation for antibodies. Genetic analysis of the isolated virus was carried out by polymerase chain reaction (PCR) and direct sequencing. The primers were designed on the basis of the major envelope gene (Env) of the Lausanne reference strain in the GenBank. The viral proteins were examined by SDS-PAGE. The isolated virus (ref. no.: BP04/2001) was able to infect the susceptible animals directly, by contact. The disease was characterised by respiratory symptoms of the upper tracheal tract, conjunctivitis and high mortality by the 11th-14th day. Aerogenic infection with strain BP04/2001 resulted in 100% morbidity among the susceptible animals. Sequencing of the amplified 400-bp-long DNA revealed 97% homology with the Env gene of the Lausanne strain, which proves that strain BP04/2001 is a variant of the Lausanne strain having been enzootic throughout Europe. The live vaccine strain used in Hungary against myxomatosis, which is also a Lausanne-derived strain, protected the animals. According to the protein analysis a protein of 200 kDa in size is not expressed in strain BP04/2001. This is the first report on atypical myxomatosis in Central Europe. The virus spreads by airborne transmission and may cause severe losses in the rabbit population.