Porcine Reproductive And Respiratory Syndrome Virus Inoculation Research Articles

208 The antiviral and immunomodulating properties from glycerides of lauric acid in PRRSV-infected PAM cells

Abstract The objective of this study was to assess the ability of a commercially available blend of glycerides of C12 to inhibit porcine reproductive and respiratory syndrome virus (PRRSV) replication in porcine alveolar macrophages (PAM) and to investigate the immunomodulatory effect during PRRSV infection in vitro. PAM were collected by lung lavage from 4-wk-old piglets, free of PRRSV. PRRSV strain 13V091 was used in this study and a commercially available mixture of mono-, di- and tri-glycerides of lauric acid (GC12). The product concentrations tested were 0.022% (T1), 0.044% (T2) and 0.088% (T3). Three different infection assays were used: (1) Co-incubation; PRRSV was inoculated together with GC12 for 1 h, (2) Pre- and Post-infection; GC12 was added to PAM cells for 24 h before infection and after 1 h of incubation for another 24 h, and (3) Post-infection; GC12 was added only after PRRSV infection for 24 h. Titration of the progeny virus was performed on PAM from all three infection assays. Cytokine analysis was only performed for infection assay 2 and 3. Collected supernatants were subjected to multiplex ELISA to measure the level of TNF-α and IL-8. Two-tailed t test P value was used to determine statistically significant differences. P < 0.05 was considered to be statistically significant. Addition of GC12 in the Co-incubation assay did not reduce PRRSV infectivity at 24-h post infection (hpi; Table 1). In contrast, the Pre- and Post-infection assay showed significantly reduced PRRSV titer from 6 hpi onwards at concentration 0.044%. At concentration 0.088% a significant reduction was observed at 24 hpi. Addition of GC12 after PRRSV inoculation (post-infection) also showed significantly reduced PRRSV titer from 6 hpi onwards at concentration 0.044% and 0.088%. In the Pre- and Post-infection assay, all treatments with GC12 numerically increased the production of TNF-α at 24 hpi. A dose response effect was observed at 24 hpi with increasing concentrations of GC12 resulting in increasing levels of TNF-α. However, in the Post-infection assay only treatment with 0.088% GC12 numerically increased the production of TNF-α by 1.5-fold. Compared with the control (PAM+PRRSV), a significantly greater concentration of IL-8 was observed with 0.044% (P = 0.019) and 0.088% (P = 0.007) GC12 24 hpi in the Pre- and Post-infection assay (1,806 ± 376; 3,751 ± 636; 3,439 ± 420 pg/mL respectively). These two concentrations resulted in numeric increase of IL-8 24 hpi in the Post-infection assay and no effect was observed with 0.022% GC12 (Control 2,332 ± 998; T1 2,079 ± 964; T2 3,525 ± 344; T3 4,475 ± 295). From this study it can be concluded that GC12 exhibited antiviral activity against PRRSV strain 13V091 and influences the cytokine production of PAM during PRRSV infection, potentially neutralizing the suppression of the immune response by PRRSV.

Porcine reproductive and respiratory syndrome virus induces tight junction barrier dysfunction and cell death in porcine glandular endometrial epithelial cells

Reproductive failure caused by porcine reproductive and respiratory syndrome virus (PRRSV) is characterized by embryonic death and weak-born piglets and is associated with placental cell apoptosis and impairment of endometrial integrity. Here, we aimed to determine whether endometrial epithelial barrier function and viability were altered following PRRSV type 1 or type 2 infection. PRRSV inoculation was examined at the apical or basolateral side of porcine glandular endometrial epithelial cell cultures isolated from 4- to 6-month-old PRRSV-free herd gilts (n = 7 pigs). On the apical side, four days postinfection (4 dpi) with type 2 PRRSV, transepithelial electrical resistance decreased by 31% ± 5%, and paracellular permeability to fluorescein isothiocyanate-dextran (4 kDa) increased by 10-fold as compared with the mock and type 1 infection. Real-time polymerase chain reaction results revealed that both PRRSV types upregulated the mRNA expression of the barrier builder tight junction protein (TJ) Cldn5, but downregulated pore-forming TJ Cldn7. Additionally, the expression of other TJ genes, i.e., Cldn3 and Cldn8, was differentially increased by PRRSV type 1 and that of zonula occludens-1 was increased by PRRSV type 2. MTT assays indicated an increase in porcine glandular endometrial epithelial cell culture at 2–6 dpi following type 2 infection. Analysis of apoptosis using Annexin/propidium iodide staining combined with flow cytometry showed that the percentage of viable cells decreased, accompanied by a significantly higher dead cell population following PRRSV type 2 infection at 2–4 dpi. PRRSV type 1 infection also induced dead cells (>4%) at 2 dpi; however, the cell population recovered at 4 dpi. In conclusion, PRRSV type 2 infection caused more severe TJ barrier dysfunction and reduced cell viability compared with PRRSV type 1 infection in the porcine endometrium. Impairment in the membrane integrity of the maternal glandular endometrium may be the underlying mechanism of PRRSV-induced reproductive failure in pregnant sows.

Highly Pathogenic PRRSV-Infected Alveolar Macrophages Impair the Function of Pulmonary Microvascular Endothelial Cells.

The porcine reproductive and respiratory syndrome virus (PRRSV), especially the highly pathogenic strains, can cause serious acute lung injury (ALI), characterized by extensive hemorrhage, inflammatory cells and serous fluid infiltration in the lung vascular system. Meanwhile, the pulmonary microvascular endothelial cells (PMVECs) are essential for forming the air–blood barrier and keeping the water–salt balance to prevent leakage of circulating nutrients, solutes, and fluid into the underlying tissues. As well, they tightly regulate the influx of immune cells. To determine the possible relationship between the PMVECs’ function changes and lung vascular permeability during PRRSV infection, the PMVECs were co-cultured with HP-PRRSV-inoculated primary pulmonary alveolar macrophages (PAMs) in transwell model, and then the RNA sequencing (RNA-seq) and comprehensive bioinformatics analysis were carried out to characterize the dynamic transcriptome landscapes of PMVECs. In total, 16,489 annotated genes were identified, with 275 upregulated and 270 downregulated differentially expressed genes (DEGs) were characterized at both 18 and 24 h post PRRSV inoculation. The GO terms and KEGG pathways analysis indicated that the immune response, metabolic pathways, cell death, cytokine–cytokine receptor interaction, viral responses, and apoptotic process are significantly regulated upon co-culture with PRRSV-infected PAMs. Moreover, according to the TERR and dextran flux assay results, dysregulation of TJ proteins, including CLDN1, CLDN4, CLDN8, and OCLN, is further confirmed to correlate with the increased permeability of PMVECs. These transcriptome profiles and DEGs will provide valuable clues for further exploring the roles of PMVECs in PRRSV-induced ALI in the future.

Silence of TGF-β1 gene expression reduces prrsv replication and potentiates immunity of immune cells of tibetan pig

Transforming growth factor beta 1 (TGF-β1) was of importance in the pathogenesis of porcine reproductive and respiratory syndrome virus (PRRSV). To determine whether knockdown of TGF-β1 gene expression could facilitate the control of PRRSV infection, specific sequences for expressing shRNA targeted to porcine TGF-β1 gene were synthesized and cloned into pSilencer 3.1-H1 neovector. Then they were used to transfect peripheral blood mononuclear cells of Tibetan pig (Tp-PBMCs) followed by PRRSV inoculation. The positive recombinant plasmids were screened for inhibition of TGF-β1 gene expression by real-time quantitative RT-PCR. Conversely, the mRNA level of PRRSV in shRNA treated Tp-PBMCs dramatically decreased, and there were significant increases of the transcription of immune genes, such as interleukin-2 (IL-2), interleukin-4 (IL-4), interferon-alpha (IFN-α), interferon-gamma (IFN-γ), tumor necrosis factor-alpha (TNF-α), toll-like receptor 3 (TLR3), toll-like receptor 7 (TLR7), Myeloid differentiation primary response gene (88) (MyD88), and interleukin-27p28 (IL-27p28). However, the expressions of IL-8 and IL-10 genes significantly reduced in comparison to the control infected cells. In addition, transfection with the shRNA plasmids significantly elevated the viability of immune cells. Therefore the knockdown of TGF-β1 gene expression by shRNA not only inhibits the replication of PRRSV but also improves immune responsiveness following viral infection, suggesting a novel way to facilitate the control of PRRSV infection in pigs.

Global miRNA, lncRNA, and mRNA Transcriptome Profiling of Endometrial Epithelial Cells Reveals Genes Related to Porcine Reproductive Failure Caused by Porcine Reproductive and Respiratory Syndrome Virus.

Porcine reproductive and respiratory syndrome virus (PRRSV) can cause respiratory disease and reproductive failure in pregnant pigs. Previous transcriptome analyses in susceptive cells have mainly concentrated on pulmonary alveolar macrophages (PAM) and Marc-145 cells, and on the respiratory system. Some studies reported that apoptosis of placental cells and pig endometrial epithelial cells (PECs) is an obvious sign linked to reproductive failure in pregnant sows, but the mechanism is still unknown. In this study, Sn-positive PECs were isolated and apoptosis rates were assessed by flow cytometry. PRRSV-infected PECs exhibited apoptosis, indicative of their susceptibility to PRRSV. Subsequently, the whole transcriptome was compared between mock- and PRRSV-infected PECs and 54 differentially expressed microRNAs (DEmiRNAs), 104 differentially expressed genes (DEGs), 22 differentially expressed lncRNAs (DElncRNAs), and 109 isoforms were obtained, which were mainly enriched in apoptosis, necroptosis, and p53 signal pathways. Integration analysis of DEmiRNA and DEG profiles revealed two microRNAs (ssc-miR-339-5p and ssc-miR-181d-5p) and five genes (SLA-DQB1, THBS1, SLC3A1, ZFP37, and LOC100517161) participating in the apoptosis signal, of which THBS1 and SLC3A1 were mainly linked to the p53 pathway. Integration analysis of DEGs with DElncRNA profiles identified genes involved in apoptosis signal pathway are regulated by LTCONS_00010766 and LTCONS_00045988. Pathway enrichment revealed that the phagosome and p53 pathways are the two main signals causing apoptosis of PECs, and functional analysis revealed a role of miR-339-5p in regulating apoptosis of PECs after PRRSV inoculation.

Immune system stimulation induced by porcine reproductive and respiratory syndrome virus alters plasma free amino acid flux and dietary nitrogen utilization in starter pigs1.

Changes in plasma free amino acid (AA) flux reflect the modification of AA metabolism in different metabolic states. Infectious diseases repartition AA away from protein retention toward processes involved in immune defense, thus impacting AA utilization in pigs. The current study sought to evaluate the effects of disease induced by a live pathogen on plasma free AA flux and whole-body nitrogen (N) utilization. Twenty gilts (BW 9.4 ± 0.9 kg) were surgically catheterized into the jugular vein, individually housed in metabolism crates, and feed-restricted (550 g/d). Intramuscular inoculation of a live field strain of porcine reproductive and respiratory syndrome virus (PRRSV) was used to induce disease. Whole-body N-balance was conducted across 3 d both before PRRSV inoculation (PRRSV-) and also after PRRSV inoculation (PRRSV+). At the end of each N-balance period, a bolus dose of a labeled [U-13C, U-15N]-AA mixture (Ile, Leu, Lys, Met, Phe, Thr, Trp, Val, and Gln) was infused intravenously, followed by serial blood collection for measurement of isotopic enrichment. A double exponential model was fitted with plasma enrichment data for each pig and each AA, and equation parameters were used to estimate plasma free AA flux and pool size. Apparent ileal digestibility (AID) of dietary N was determined using the slaughter technique and an indigestible marker. Blood chemistry, hematology, body temperature, and serum viremia indicated that PRRSV induced effective immune response in pigs (P < 0.05). Challenge with PRRSV reduced the AID of N (P < 0.05), but had no effect on apparent total tract digestibility of dietary energy (P = 0.12). Plasma flux (µmol/kg BW/h) for Met and Thr was increased by PRRSV infection (P < 0.05). A strong tendency of increased Val flux was observed in PRRSV+ pigs (P = 0.06). Infection with PRRSV increased the pool size for Lys, Met, Thr, Trp, Leu, Val, and Gln (P < 0.05). Collectively, these results suggest that PRRSV alters the utilization of dietary N and AA flux, as well as pool size, in growing pigs. The increase in Thr and Met flux in PRRSV+ pigs may be associated with enhanced utilization of these AA for the synthesis of immune system metabolites and increased catabolism of these AA. Thus, dietary Met, Thr, and Val requirements may increase in pigs infected with PRRSV, relative to the requirements for other AA.

Knockdown expression of IL-10Rα gene inhibits PRRSV replication and elevates immune responses in PBMCs of Tibetan pig in vitro.

Increase of interleukin-10 (IL-10) induced by Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) infection has been intensely studied to inhibit the anti-viral responses of host pigs. Blockade of expression of IL-10 receptor (IL-10R) by RNA interference (RNAi) may relieve the immunosuppression caused by excessive IL-10 in PRRSV infection. The recombinant short hairpin expressing plasmid targeted to pig IL-10Rα was transfected into peripheral blood mononuclear cells of Tibetan pig (Tp-PBMCs) prior to PRRSV inoculation, then the replication of PRRSV and immune responses in Tp-PBMCs were evaluated. The recombinant interfering plasmid greatly decreased PRRSV yield. The transcriptional level of IL-10Rαwas obviously inhibited by recombinant interfering plasmid; the expression of IL-10 was also down-regulated, while that of TGF-β1 was not affected. Furthermore, the recombinant plasmid notably up-regulated the mRNA levels of TLR3, TLR7, IFN-α, IFN-γ, IL-2, IL-4, IL-12p40 and MyD88, while that of IL-8 was apparently decreased; In addition, cell viability of Tp-PBMCs was clearly enhanced by the interfering recombinant plasmid. Our results suggest that knockdown the expression of pig IL-10Rα can evidently inhibit the PRRSV infection and enhance the anti-viral immune responses of pig immune cells, which may be a promising way for preventing virus infection and developing new effective immune-regulator to strengthen the host immunity against PRRS.

The Influence of Porcine Reproductive and Respiratory Syndrome Virus Infection on the Expression of Cellular Prion Protein in Marc-145 Cells

Cellular prion protein (PrPC) represents a potential regulator of cellular immunity and has been confirmed to be an invasive receptor exploited by bacteria such as Brucella abortus to facilitate the infection in host cells. Up to now, there are few informations about the role of PrPC in virus replication in host cells. Porcine reproductive and respiratory syndrome virus (PRRSV), a single positive-stranded RNA virus, prefers to infect African green monkey kidney cell line MA-104 and its derivatives, such as Marc-145. We found that PrPC is expressed on the surfaces of Marc-145 cells and its expression profiles greatly changed after PRRSV incubation with these cells. PrPC expression reached the peak at 12 hrs after PRRSV inoculation and then decreased sharply to recover to the original status while CD163, a PRRSV receptor in Marc-145 cells, achieved the climax at 48 hrs after virus infection and then slowly lowered its expression level. Here, we firstly suggest that PRRSV infection has an influence on the expression of PrPC on the surfaces of Marc-145 cells and PrPC may be involved in PRRSV invasion of host cells.

Plasmids expressing interleukin-10 short hairpin RNA mediate IL-10 knockdown and enhance tumor necrosis factor alpha and interferon gamma expressions in response to porcine reproductive and respiratory syndrome virus

Porcine reproductive and respiratory syndrome virus (PRRSV) has been suggested to exploit interleukin-10 (IL-10) to suppress immune defense of infected pigs. The present study constructed plasmids encoding selected short hairpin RNA specific to porcine IL-10 mRNA (pIL-10sh) to knockdown IL-10 transcription and investigated the suppressive effect of PRRSV-induced IL-10 on various immune marker expressions. Naïve blood monocytes from eight PRRSV-seronegative pigs were transfected with pIL-10sh and pNeg (plasmid vector) prior to PRRSV inoculation and subsequent lipopolysaccharide (LPS) stimulation. The mRNA expressions of IL-10, IL-1β, IL-12p40, tumor necrosis factor alpha (TNFα), interferon gamma (IFNγ), transforming growth factor beta (TGFβ), CD80, and CD86 were evaluated by real-time PCR. The IL-10, TNFα, and IFNγ protein productions were determined by ELISA. Compared with non-transfected monocyte control, transfection with selected pIL-10sh (pIL-10sh1), but not other pIL-10sh nor pNeg, significantly reduced IL-10 expression and significantly enhanced TNFα and IFNγ expressions. Slight increases in IL-1β, IL-12p40, CD80, and CD86 expressions were also observed. Neither pIL-10sh1 nor pNeg transfection affected TGFβ expression. Our results indicate that PRRSV does exploit IL-10 to suppress the expressions of pro-inflammatory cytokines, mainly TNFα and IFNγ, and co-stimulatory molecules, CD80 and CD86.

Commercial spray-dried porcine plasma does not transmit porcine circovirus type 2 in weaned pigs challenged with porcine reproductive and respiratory syndrome virus

The objective of this study was to evaluate if spray dried porcine plasma (SDPP) containing porcine circovirus type 2 (PCV2) genome supplemented in feed could transmit PCV2 to pigs challenged with porcine reproductive and respiratory syndrome virus (PRRSV). Twenty-three PRRSV-free pigs, non-viraemic for PCV2, were housed in bio-safety level 3 facilities and assigned to four groups in a 2×2 factorial design consisting of PRRSV challenge and a negative control. The diet contained 0 or 8kg SDPP per 100kg of feed. PRRSV challenge groups were inoculated intranasally with 2mL of a suspension containing 10(6) TCID(50)/mL PRRSV. The SDPP used in the study contained 7.56×10(5) PCV2 genome copies per gram. Dietary treatments were fed from 4days prior to PRRSV inoculation until 28days post-inoculation (PI). All challenged pigs developed PRRSV viraemia by day 3PI and PRRSV antibodies were detected in sera by day 14PI, with no difference between diet treatments. Neither PRRSV viraemia nor seroconversion was observed in non-challenged pigs. PCV2 was not detected in the serum of any pigs throughout the experimental period. SDPP containing the PCV2 genome supplemented in feed did not result in PCV2 transmission to either healthy or PRRSV-infected pigs under these experimental conditions.

Interleukin-10 Antisense Oligodeoxynucleotide Suppresses IL-10 Expression and Effects on Proinflammatory Cytokine Responses to Porcine Reproductive and Respiratory Syndrome Virus

Upregulation of interleukin-10 (IL-10) expression has been suggested to be the mechanism by which the porcine reproductive and respiratory syndrome virus (PRRSV) suppresses the innate and adaptive immune response in infected pigs. In this study we evaluated the potential of phosphorothioate-modified IL-10 antisense oligodeoxynucleotide specific to the translation initiation region of porcine IL-10 mRNA (IL-10AS) in enhancing proinflammatory cytokine responses to PRRSV. Naïve peripheral blood mononuclear cells from eight PRRSV-seronegative pigs were transfected with IL-10AS in vitro prior to PRRSV inoculation and phorbol 12-myristate 13-acetate plus ionomycin or concanavalin A stimulation. The effects of IL-10AS on mRNA expression of IL-10, interferon-gamma (IFN-gamma), IFN-alpha, tumor necrosis factor-alpha (TNF-alpha), IL-2, and IL-4 were tested by real-time PCR. The percentages of IFN-gamma-producing T-cell subsets were determined by flow cytometry. Compared to the controls, the levels of IL-10 and IL-2 mRNA were significantly reduced, while those of IFN-gamma mRNA were increased, and TNF-alpha, IFN-alpha, and IL-4 mRNA were unchanged. An increase in the percentage of the IFN-gamma+ population was also observed in lymphocytes and CD8beta+ T cells. Our results suggest that IL-10AS has the potential to enhance proinflammatory cytokine responses to PRRSV infection.

Behaviour of pigs with viral and bacterial pneumonia

The behavioural response to infection is well organized and may enhance disease resistance and facilitate recovery, but the behaviour of pigs with an acute respiratory infection has not been assessed. Therefore, the purpose of this study was to evaluate behaviour of pigs inoculated with Mycoplasma hyopneumoniae (Mh) and porcine reproductive and respiratory syndrome virus (PRRSV). Sixty-four pigs were subjected to one of four treatment combinations (2 × 2 factorial) of Mh (inoculated at 4 weeks of age) and PRRSV (inoculated at 6 weeks of age). The four treatments were (1) control, (2) inoculation with Mh, (3) inoculation with PRRSV, and (4) inoculation with both Mh and PRRSV. One-half of the pigs from each treatment were killed 7 days after PRRSV inoculation for purposes unrelated to this study and hence were not used for behavioural analysis. Pigs that were included were video recorded during the 18 h light phase for 13 days beginning the day of PRRSV inoculation. Food intake and time spent feeding, active (standing, including walking, sitting, or feeding) and lying were determined. When pigs were lying a determination was made as to whether they were lying ventrally or laterally, and in contact with a penmate. Body temperature was measured 7 and 14 days after PRRSV inoculation. After inoculation with PRRSV, there was no significant main effect of Mh or interaction between Mh and PRRSV for food intake, body temperature, or any behaviour measured. Thus, the four treatments were pooled to form two treatments designated PRRSV negative (control and Mh; PRRSV−) and PRRSV positive (PRRSV and Mh with PRRSV; PRRSV+) and analyzed. Each day after PRRSV inoculation, PRRSV+ pigs spent less time ( P = 0.005) feeding compared to PRRSV− pigs, and the decrease in feeding time was associated with a decrease in food intake ( P < 0.001). PRRSV+ pigs decreased ( P < 0.001) activity after inoculation with PRRSV compared to PRRSV− pigs and the amount of time spent lying was greater ( P < 0.001) in PRRSV+ pigs compared to PRRSV− pigs. Furthermore, PRRSV+ pigs spent more of their total lying time in a ventral position ( P = 0.06) and in contact with a penmate ( P < 0.001) compared to PRRSV− pigs. Body temperature was increased ( P < 0.001) in PRRSV+ pigs 7 days after PRRSV inoculation. Since sickness behaviour and fever are adaptive responses to infection, these data indicate that pigs with an acute PRRSV infection evoke a behavioural strategy that may support recovery.

Decreased Protein Accretion in Pigs with Viral and Bacterial Pneumonia Is Associated with Increased Myostatin Expression in Muscle

Chronic respiratory infections reduce growth in pigs but protein accretion (PA) during an ongoing multifactorial respiratory infection has not been determined, and the mechanisms underlying growth inhibition are largely unknown. The objectives of this study were to determine whether viral and bacterial pneumonia in young pigs decrease PA, increase serum IL-1beta and IL-6, and increase myostatin (MSTN) mRNA in biceps femoris and triceps muscles. Mycoplasma hyopneumoniae (Mh) or medium was given intratracheally at 4 wk of age, Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) or medium was given intranasally at 6 wk of age, and pigs were killed 7 or 14 d after PRRSV inoculation for body composition analysis. PRRSV but not Mh induced a marked increase (P < 0.01) in IL-1beta, IL-6, and MSTN mRNA and a decrease (P < 0.01) in food intake, daily weight gain, PA, and lipid accretion. PRRSV also reduced (P < 0.01) myofiber area in the biceps femoris. Food intake, weight gain, PA, and weight of biceps femoris and triceps muscles were negatively correlated (r = -0.4 to -0.8, P < 0.05) with serum IL-1beta and IL-6 and with MSTN mRNA in muscle. These results suggest that the magnitude of increases in inflammatory cytokines during a respiratory infection may be predictive of decreases in PA and growth. They further suggest that during infection growth of skeletal muscle is limited in part by myostatin.

Effects of Dietary Zinc on Performance and Immune Response of Growing Pigs Inoculated with Porcine Reproductive and Respiratory Syndrome Virus and Mycoplasma hyopneumoniae

The objective of this study was to determine the effects of dietary Zn level on performance, serum Zn concentrations, alkaline phosphatase activity (ALP), and immune response of pigs inoculated with Porcine Reproductive and Respiratory Syndrome virus (PRRSv) and Mycoplasma hyopneumoniae. A 2×4 factorial arrangement of treatments was used in a randomized design. Factors included; 1) PRRSv and M. hyopneumoniae inoculation (n=36 pigs) or sham inoculation (n=36 pigs) with media when pigs entered the grower facility (d 0) at 9 weeks of age and 2) 10, 50, 150 ppm supplemental Zn sulfate (ZnSO4) from weaning until the completion of the study, or 2,000 ppm supplemental ZnSO4 for two weeks in the nursery and then supplementation with 150 ppm ZnSO4 for the remainder of the trial. The basal diet contained 34 ppm Zn. Pigs were weighed on d 0, 10, 17, 24 and 31 and blood samples were collected on d 0, 7, 14, 21 and 28. Pigs inoculated with PRRSv were serologically positive at d 28 and control pigs remained negative to PRRSv. In contrast, the M hyopneumoniae inoculation was inconsistent with 33.3% and 52.8% of pigs serologically positive at d 28 in the control and infected groups, respectively. A febrile response was observed for approximately one week after inoculation with PRRSv. Feed intake (p<0.01) and gain (p<0.1) were less in PRRSv infected pigs than control pigs for the 31 d study. However, performance did not differ among pigs in the four levels of ZnSO4. Assessments of immune responses failed to provide unequivocal influence of either PRRSv inoculation or ZnSO4 level. These data suggest that PRRSv and M. hyopneumoniae act to produce some performance deficits and the influence of Zn supplementation of nursery age pigs does not have clear effect in grower pigs affected with disease. (Asian- Aust. J. Anim. Sci. 2004. Vol 17, No. 10 : 1438-1446)

Mycoplasma hyopneumoniae potentiation of porcine reproductive and respiratory syndrome virus-induced pneumonia.

An experimental model that demonstrates a mycoplasma species acting to potentiate a viral pneumonia was developed. Mycoplasma hyopneumoniae, which produces a chronic, lymphohistiocytic bronchopneumonia in pigs, was found to potentiate the severity and the duration of a virus-induced pneumonia in pigs. Pigs were inoculated with M. hyopneumoniae 21 days prior to, simultaneously with, or 10 days after inoculation with porcine reproductive and respiratory syndrome virus (PRRSV), which induces an acute interstitial pneumonia in pigs. PRRSV-induced clinical respiratory disease and macroscopic and microscopic pneumonic lesions were more severe and persistent in M. hyopneumoniae-infected pigs. At 28 or 38 days after PRRSV inoculation, M. hyopneumoniae-infected pigs still exhibited lesions typical of PRRSV-induced pneumonia, whereas the lungs of pigs which had received only PRRSV were essentially normal. On the basis of macroscopic lung lesions, it appears that PRRSV infection did not influence the severity of M. hyopneumoniae infection, although microscopic lesions typical of M. hyopneumoniae were more severe in PRRSV-infected pigs. These results indicate that M. hyopneumoniae infection potentiates PRRSV-induced disease and lesions. Most importantly, M. hyopneumoniae-infected pigs with minimal to nondetectable mycoplasmal pneumonia lesions manifested significantly increased PRRSV-induced pneumonia lesions compared to pigs infected with PRRSV only. This discovery is important with respect to the control of respiratory disease in pigs and has implications in elucidating the potential contribution of mycoplasmas in the pathogenesis of viral infections of other species, including humans.