Elida M. Bautista

Experimental porcine reproductive and respiratory syndrome virus infection in one-, four-, and 10-week-old pigs.

One-, 4-, and lo-week-old pigs were exposed to porcine reproductive and respiratory syndrome virus (PRRSV) to determine the effect of age on clinical signs, hematologic alterations, the onset and duration of viremia, routes of virus shedding, antibody production, and microscopic lesions produced by PRRSV isolate ATCC VR-2332. The response to PRRSV infection was similar among age groups. Fever, usually prolonged, and a marked dyspnea with cutaneous erythema when restrained for sample collection were the most consistent clinical signs. Prolonged periocular edema was unique to the 1-week-old pigs. The white blood cell count was decreased on day 4 postexposure (PE) due to decreases in neutrophils and lymphocytes. The virus was isolated from buffy coats at day 1 PE and was isolated from serum, buffy coat, or plasma at each sample collection period through the end of the trial (day 28 PE). Virus was most consistently isolated from lung, lymph node, spleen, and tonsil on day 7 PE and exclusively from lymph node, spleen, and tonsil on day 28 PE. Virus was infrequently isolated from urine and fecal and nasal swabs. Consistent microscopic changes in all age groups included interstitial pneumonia and lymph node hypertrophy and hyperplasia on days 7 and 28 PE, lymph node necrosis on day 7 PE, and subacute mononuclear myocarditis on day 28 PE. Findings presented here indicate that interstitial pneumonia, lymphoid necrosis, and mononuclear myocarditis are characteristic lesions of PRRSV isolate ATCC VR-2332 infection in 1-, 4-, and lo-week-old pigs.

Comparison of Porcine Alveolar Macrophages and CL 2621 for the Detection of Porcine Reproductive and Respiratory Syndrome (PRRS) Virus and Anti-PRRS Antibody

The American and European strains of porcine reproductive and respiratory syndrome (PRRS) virus were initially isolated in an established cell line (CL 2621) and porcine alveolar macrophages (PAM), respectively. Subsequent isolation of American strains of this virus in PAM has also been reported. To determine their relative sensitivity for virus isolation, both PAM and CL 2621 cells were inoculated with 98 tissue specimens and 73 serum samples from animals suspected of having PRRS. Four of the 98 tissue samples yielded virus in both cell types, whereas 7 samples were positive only in PAM and 4 samples only in CL 2621. Of the 73 serum samples tested, 18 were positive in PAM of which only 2 were positive in CL 2621. Additionally, 82 isolates obtained initially in CL 2621 were inoculated in PAM cells, and 18 strains isolated originally in PAM were inoculated in CL 2621. Of the 82 CL 2621 isolates, 25 could not be propagated on PAM. Of the 57 that replicated in PAM, as detected by a positive test on indirect fluorescent antibody test, only 28 produced cytopathic effects and 29 did not. Of the 18 PAM isolates, 5 did not grow on CL 2621. Although PAM were relatively more sensitive for virus isolation, their failure to support the growth of certain strains of PRRS virus indicates the existence of variants among PRRS virus strains, and both PAM and CL 2621 should be used for virus isolation from clinical samples. In addition, the sensitivity of these 2 cell types was compared for the detection of fluorescent antibodies to PRRS virus using 179 serum samples from PRRS-infected animals. The results were comparable in both cell systems.

IFNγ inhibits porcine reproductive and respiratory syndrome virus replication in macrophages

SummaryThis study reports the effect of IFNγ on the replication of porcine reproductive and respiratory syndrome virus (PRRSV) in macrophages. Pretreatment with IFNγ profoundly affected PRRSV replication in porcine macrophages evaluated by reduction in titer and percentage of positive cells. The effect of IFNγ on PRRSV replication was both dose-dependent and related to the time of exposure. The mechanism of action was not due to blocking virus attachment. The inhibitory effect on PRRSV replication in macrophages suggests that IFNγ may play an important role in protection.

Immunity to PRRSV: Double-edged sword

Abstract The immune system is a double-edged sword for porcine reproductive and respiratory syndrome virus (PRRSV) infection. On one edge PRRSV has a predilection for immune cells and the disease manifestations can be linked directly to changes in the immune system. PRRSV appears to replicate extensively, if not exclusively, in cells of the immune lineage, notably macrophages; the direct replication of which may lead to immunosuppression, precipitate secondary infection and/or mediate disease. On the other edge, the virus stimulates immunity post-infection that protects an animal from re-infection. A vast array of structural and functionally distinct antibody specific to PRRSV are generated following infection or vaccination. Discrete populations of functional antibodies appear at different times and possibly reflect reactivity to different PRRSV polypeptides. Cell-mediated immune responses specific to PRRSV can be detected in various exposed pigs as well. Thus, the immune system appears to be intimately involved in both the disease process and protection from disease. It is unclear at this state of understanding what immune compartment provides protective immunity. Is it humoral (i.e. antibodies), selective functionally distinct populations of antibodies specific for selected PRRSV polypeptides or is cellular immunity essential for protection, or both. This review will attempt to summarize the current state of knowledge of the complex interaction of the immune system and PRRSV.

T cell responses to the structural polypeptides of porcine reproductive and respiratory syndrome virus

SummaryThe identification of antigens recognized by T cell responses has become fundamental for developing effective immunizations against viral infections. Lymphocyte proliferation and delayed-type hypersensitivity responses to porcine reproductive and respiratory syndrome virus (PRRSV) infection have been demonstrated. However, the polypeptide specificity of T cell responses to PRRSV is unknown. To identify the PRRSV polypeptides recognized by porcine lymphocytes two approaches were employed. First polypeptides of purified virions were separated by SDS-PAGE and particle suspensions obtained from nitrocellulose blots were used as antigens. Second, the polypeptides encoded by ORFs 2, 4, 5, 6, and 7 of the strain VR-2 332 were expressed as fusion proteins with a histidine tag in mammalian cells, using vaccinia virus as expression system. Significant antigen-specific proliferation responses to the matrix and envelope proteins from purified virions were obtained. This finding was supported by specific and dose-dependent proliferation responses to the recombinant polypeptides encoded by ORF2, 5 and 6 detected in virus-infected but not in control pigs. These results demonstrate that T-cell responses can be detected to individual PRRSV polypeptides. The greater response to the product of ORF6 than to the other PRRSV polypeptides indicates that the viral matrix polypeptide may have a major role in cellular immunity.

Structural polypeptides of the American (VR-2332) strain of porcine reproductive and respiratory syndrome virus.

SummaryThe structural polypeptides of the isolate VR-2332 of porcine reproductive and respiratory syndrome virus were analyzed in sucrose gradient-purified virions. The virus had an average density of 1.15 g/cm3 and contained, by SDS-PAGE, three major polypeptides with apparent molecular weights of 15, 19 and 26–30 kDa, which were designated as nucleocapsid (N), matrix (M) and envelope (E), respectively. The predominant structural protein was N. N-glycosidase F digestion only affected E whereas O-glycosidase or endoglycosidase H digestion had no effect, suggesting that the viral glycoproteins contain only complex N-linked carbohydrates.

Serologic Survey for Lelystad and VR-2332 Strains of Porcine Respiratory and Reproductive Syndrome (PRRS) Virus in US Swine Herds

Viral infection of the monocyte-macrophage system of this pigeon demonstrated by both light and transmission electron microscopy suggests that the virus may interfere with antigen processing in pigeons, as is speculated in psittacine birds with PBFD. Multiple infections with bacteria (Chlamydia psittaci, Pasteurella sp., and an enteropathogenic coccobacillus), parasites (Tetrameres sp., and Trichomonas sp.), and viruses (presumptive paramyxovirus or herpesvirus) suggest that acquired immunodeficiency was associated with the circoviruslike agent. Immunohistochemistry, DNA in situ hybridization, and polymerase chain reaction with DNA dot-blot hybridization indicate that this pigeon circa-like virus is distinct from PBFD virus with respect to antigenicity and nucleic acid sequence. However, both viruses are similar with respect to suggestion of acquired immunodeficiency and association with a plethora of secondary infections.