The survival of Salmonella anatum, pseudorabies virus and porcine reproductive and respiratory syndrome virus in swine slurry

The survival of Salmonella anatum, pseudorabies virus (PRV), and porcine reproductive and respiratory syndrome virus (PRRSV) in swine slurry was studied at different temperature (4 degrees C, 25 degrees C, and 37 degrees C) and pH (4.0, 7.0, and 10.0) conditions. The longest survival of S. anatum (56 days) was observed at 4 degrees C and pH 7.0. The pseudorabies and the PRRS viruses also survived the longest at 4 degrees C and pH 7.0 but were inactivated within 8 and 14 days, respectively.

Virus quantification and identification of cellular targets in the lungs and lymphoid tissues of pigs at different time intervals after inoculation with porcine reproductive and respiratory syndrome virus (PRRSV)

Sixteen 6 week old conventional pigs were inoculated by aerosol with a European strain of porcine reproductive and respiratory syndrome virus (PRRSV). Virus replication was followed by virus titration and immunofluorescence in the lungs and in associated and distant lymphoid tissues at 3, 14, 21, 35, 42 and 82 days post-inoculation (DPI). PRRSV replication was detected in alveolar macrophages, lungs, tonsils, spleen, retropharyngeal lymph nodes, bronchial lymph nodes and thoracic aortic lymph nodes at 3 DPI. The same tissues, except retropharyngeal and thoracic aortic lymph nodes, were PRRSV positive at 14 DPI. Lungs and alveolar macrophages were PRRSV positive until 35 DPI. PRRSV was not detected in heart, peripheral blood mononuclear cells and bone marrow cells. Viremia was detected from 3 to 28 DPI. Not more than 2% of alveolar macrophages were PRRSV positive even during the acute stage of infection. 80 to 94% of the PRRSV infected cells in the lungs and in lung lavaged cells were identified as macrophages using a porcine macrophage specific monoclonal antibodies. In the lymph nodes and spleen, 100% of the infected cells were macrophages. Anti-PRRSV antibodies were detected by a blocking ELISA as early as 7 DPI. the antibody titre gradually increased to reach a geometric mean titre (GMT) of 160 at 35 DPI. It remained at that level until the end of the study. These findings clearly demonstrate that PRRSV has a tropism for macrophages. PRRSV mainly replicates in macrophages of the lymphoid tissues and lungs in the acute phase of infection and persists in the lung macrophages.

Effect of heparin on infection of cells by porcine reproductive and respiratory syndrome virus

OBJECTIVE

To investigate whether heparin has any effect on the growth of porcine reproductive and respiratory syndrome virus (PRRSV).

SAMPLE POPULATION

2 isolates of PRRSV, and as control viruses, 1 isolate of pseudorabies virus (PRV) and 1 isolate of parainfluenza 3 virus (PIV-3).

PROCEDURES

Plaque assays, using a continuous cell line (MARC-145) derived from African green monkey kidney cell line (MA104), were performed for determination of inhibitory effect of heparin on PRRSV, PRV, and PIV-3. The effect of various doses of heparin and heparinase on the growth of PRRSV, PRV, and PIV-3 was evaluated and compared. In each experiment, value were expressed as the mean value for duplicate samples.

RESULTS

The number of plaques formed by PRRSV and PRV was reduced to 24 to 25 and 15% of the untreated control (100%), respectively, by 1 U of heparin/ml, but could not be reduced below 6 to 7 and 3%, respectively, by use of concentrations up to 50 U/ml. An inhibitory effect of heparin, at a concentration up to 50 U/ml, was not observed on PIV-3. Delaying addition of heparin for 30 minutes after the addition of PRRSV and PRV reduced plaque formation by 48 to 51 and 68%, respectively, compared with 91 to 92 and 95%, respectively, if heparin was added at the time of infection. In addition, most PRRSV added was retained by heparin beads, as was PRV. Heparinase treatment of MARC-145 cells reduced the number of PRRSV-, as well as PRV-induced plaques. On the other hand, the number of PIV-3-induced plaques did not decrease after treatment of MARC-145 cells with heparinase.

CONCLUSIONS

Addition of heparin to PRRSV or to the MARC-145 cells before virus inoculation and treatment of the cells with heparinase prevented the virus from infecting the cells.

Comparative morphogenesis of three PRRS virus strains

The morphogenesis of a Dutch PRRS field strain virus (Lelystad virus) was studied and compared to that of a U.S. field strain VR2332 and its attenuated vaccine strain JJ1882. Porcine lung alveolar macrophages (PLAM) and CL2621 cells were infected with high doses of virus (MOI = 10). At 4, 6, 9, 12, 18, 24, and 48 h post infection (hpi) cells were fixed for electronmicroscopy or for detection of viral antigens by immunoperoxidase staining. From 6 hpi on, viral antigens were detected in the cytoplasm and from 9 hpi on completely assembled virus particles could be detected in infected cells. The three strains were similar in assembly of new virus particles, envelopment at the smooth endoplasmic reticulum, and egress from infected cells. However, distinct differences were seen in replication time of the three strains in various cell types. The Lelystad virus replicated very fast and efficiently in PLAM while VR2332 and JJ1882 replicated preferably in CL2621 cells. JJ1882 replicated faster in CL2621 cells than VR2332 did, probably because of increased adaptation to the cell-line. Although the U.S. and European strains differ at the level of the genome, morphogenesis is not visibly altered. There is however a distinct difference in preferred cell type between the European strain and the two U.S. strains.

Efficacy of an inactivated vaccine for prevention of reproductive failure induced by porcine reproductive and respiratory syndrome virus

This report describes the results of experiments with an inactivated oily vaccine containing per dose about 10(5.5) median tissue culture infectious dose (TCID50) of the Spanish strain of porcine reproductive and respiratory syndrome (PRRS) virus grown in porcine alveolar macrophages (PAMs). In order to evaluate the efficacy of the vaccine, two experimental infection routes were tested in sows; subsequent intranasal (i.n.) and intravenous (i.v.) (out of a total of 93 piglets born to 7 sows, 16% were mummified, 18.2% were weak and died within 48 h of birth, 37% were stillborn, 5.3% died between 2 and 7 days of age, 22.5% lived for more than one week) and intranasal alone (out of a total of 65 piglets born to 5 sows, 0% were mummified, 22.5% were weak and died within 48 h of birth, 40% were stillborn, 4.6% lived for more than one week). I.N. alone was selected to evaluate the efficacy of the vaccine because this is the natural route of infection. A number of experiments were conducted to test the immunogenicity of the vaccine. In general, after challenge with the homologous strain, protection in vaccinated sows was high (at least 70% of the piglets were born alive and healthy), whereas protection in unvaccinated sows was low (only 10% of the piglets were born alive and healthy). Vaccinated animals devoid of antibodies by immunoperoxidase monolayer assay (IPMA) at the time of challenge were still protected at experimental infection.

Slow-reacting and complement-requiring neutralizing antibody in swine infected with porcine reproductive and respiratory syndrome (PRRS) virus

Various conditions were evaluated and modified to enhance the sensitivity of the neutralization (NT) test for detecting antibody in swine infected with porcine reproductive and respiratory syndrome (PRRS) virus. Higher NT antibody titers were consistently obtained by the addition of 10% (v/v) complement, fresh guinea pig serum, to the virus diluent and by the incubation of serum-virus mixture at 4 degrees C for 24 hr. The appearance and persistence of antibodies detected by the modified NT test showed a similar pattern to those of antibodies detected by the indirect fluorescent antibody (IFA) assay, although the antibody titers obtained by the former method were consistently lower than those obtained by the latter method. Slow-reacting complement-requiring NT antibody was detected in sera from pig 2 weeks after infection with PRRS virus. The slow-reacting complement-requiring NT antibody in the early serum samples was sensitive to 2-mercaptoethanol (2-ME), whereas the slow-reacting complement-requiring NT antibody in the late serum samples was resistant to 2-ME. The initial phase may represent the IgM response and the later phase a change to IgG. A NT test was developed in which serum-virus mixtures were incubated at 4 degrees C for 24 hr with complement; this gave an improved sensitivity over the previous incubation at 37 degrees C for 60 min.