Immuno-modulating properties of Tulathromycin in porcine monocyte-derived macrophages infected with porcine reproductive and respiratory syndrome virus

Repositioning of Antibiotics in the Treatment of Viral Infections

Drug repurposing, also known as drug repositioning, is a currently tested approach by which new uses are being assigned for already tested drugs. In this case there are antibiotics that are used to combat bacterial infections. However, antibiotics are among the drugs that have been studied for possible antiviral activities. Therefore, the aim of this work is to carry out a review of the studies of antibiotics that could be repositioned for the treatment of viral infections. Among the main antibiotics that have demonstrated antiviral activity are macrolides and glycopeptides. In addition, several antibiotics from the group of tetracyclines, fluoroquinolones, cephalosporins and aminoglycosides have also been studied for their antiviral activity. These antibiotics have demonstrated antiviral activity against both RNA and DNA viruses, including the recent pandemic virus SARS-CoV-2. Some of these antibiotics were selected in addition to its antiviral activity for their immunomodulatory and anti-inflammatory properties. Of the antibiotics that present antiviral activity, in many cases the mechanisms of action are not exactly known. The use of these antibiotics to combat viral infections remains controversial and is not generally accepted, since clinical trials are required to prove its effectiveness. Therefore, there is currently no antibiotic approved as antiviral therapy. Hence is necessary to present the studies carried out on antibiotics that can be repositioned in the future as antiviral drugs.

Characterizing the influence of various antimicrobials used for metaphylaxis against bovine respiratory disease on host transcriptome responses

Currently, control against bovine respiratory disease (BRD) primarily consists of mass administration of an antimicrobial upon arrival to facility, termed "metaphylaxis." The objective of this study was to determine the influence of six different antimicrobials used as metaphylaxis on the whole blood host transcriptome in healthy steers upon and following arrival to the feedlot. One hundred and five steers were stratified by arrival body weight (BW = 247 ± 28 kg) and randomly and equally allocated to one of seven treatments: negative control (NC), ceftiofur (CEFT), enrofloxacin (ENRO), florfenicol (FLOR), oxytetracycline (OXYT), tildipirosin (TILD), or tulathromycin (TULA). On day 0, whole blood samples and BW were collected prior to a one-time administration of the assigned antimicrobial. Blood samples were collected again on days 3, 7, 14, 21, and 56. A subset of cattle (n = 6) per treatment group were selected randomly for RNA sequencing across all time points. Isolated RNA was sequenced (NovaSeq 6,000; ~35 M paired-end reads/sample), where sequenced reads were processed with ARS-UCD1.3 reference-guided assembly (HISAT2/StringTie2). Differential expression analysis comparing treatment groups to NC was performed with glmmSeq (FDR ≤ 0.05) and edgeR (FDR ≤ 0.1). Functional enrichment was performed with KOBAS-i (FDR ≤ 0.05). When compared only to NC, unique differentially expressed genes (DEGs) found within both edgeR and glmmSeq were identified for CEFT (n = 526), ENRO (n = 340), FLOR (n = 56), OXYT (n = 111), TILD (n = 3,001), and TULA (n = 87). At day 3, CEFT, TILD, and OXYT shared multiple functional enrichment pathways related to T-cell receptor signaling and FcεRI-mediated NF-kappa beta (kB) activation. On day 7, Class I major histocompatibility complex (MHC)-mediated antigen presentation pathways were enriched in ENRO and CEFT groups, and CEFT and FLOR had DEGs that affected IL-17 signaling pathways. There were no shared pathways or Gene Ontology (GO) terms among treatments at day 14, but TULA had 19 pathways and eight GO terms enriched related to NF- κβ activation, and interleukin/interferon signaling. Pathways related to cytokine signaling were enriched by TILD on day 21. Our research demonstrates immunomodulation and potential secondary therapeutic mechanisms induced by antimicrobials commonly used for metaphylaxis, providing insight into the beneficial anti-inflammatory properties antimicrobials possess.

Synergistic Effect of Treatment with Highly Pathogenic Porcine Reproductive and Respiratory Syndrome Virus and Lipopolysaccharide on the Inflammatory Response of Porcine Pulmonary Microvascular Endothelial Cells

The highly pathogenic porcine reproductive and respiratory syndrome virus (HP-PRRSV) often causes secondary bacterial infection in piglets, resulting in inflammatory lung injury and leading to high mortality rates and significant economic losses in the pig industry. Microvascular endothelial cells (MVECs) play a crucial role in the inflammatory response. Previous studies have shown that HP-PRRSV can infect porcine pulmonary MVECs and damage the endothelial glycocalyx. To further understand the role of pulmonary MVECs in the pathogenesis of HP-PRRSV and its secondary bacterial infection, in this study, cultured porcine pulmonary MVECs were stimulated with a HP-PRRSV HN strain and lipopolysaccharide (LPS). The changes in gene expression profiles were analyzed through transcriptome sequencing, and the differentially expressed genes were verified using qRT-PCR, Western blot, and ELISA. Furthermore, the effects on endothelial barrier function and regulation of neutrophil trans-endothelial migration were detected using the Transwell model. HP-PRRSV primarily induced differential expression of numerous genes associated with immune response, including IFIT2, IFIT3, VCAM1, ITGB4, and CCL5, whereas LPS triggered an inflammatory response involving IL6, IL16, CXCL8, CXCL14, and ITGA7. Compared to the individual effect of LPS, when given after HN-induced stimulation, it caused a greater number of changes in inflammatory molecules, such as VCAM1, IL1A, IL6, IL16, IL17D, CCL5, ITGAV, IGTB8, and TNFAIP3A, a more significant reduction in transendothelial electrical resistance, and higher increase in neutrophil transendothelial migration. In summary, these results suggest a synergistic effect of HP-PRRSV and LPS on the inflammatory response of porcine pulmonary MVECs. This study provides insights into the mechanism of severe lung injury caused by secondary bacterial infection following HP-PRRSV infection from the perspective of MVECs, emphasizing the vital role of pulmonary MVECs in HP-PRRSV infection.

Pattern of Antibiotic Consumption in Two Italian Production Chains Differing by the Endemic Status for Porcine Reproductive and Respiratory Syndrome

The aim of this case study was to quantify antibiotic (AB) use in Italian weaning (W) and fattening (F) units differentiated for porcine reproductive and respiratory syndrome (PRRS) occurrence. Farms were classified as either PRRS negative (–) or PRRS positive (+) based on the circulation of the virus among the animals. In all the farms, the modified live PRRS virus (PRRSV) vaccine was provided to all the animals. In the PRRS– farms, the level of circulating antibodies was low, and the disease, in its clinical form, did not occur. In the PRRS+ farms, the level of circulating antibodies against the virus was high, and the disease was recurrent. Data regarding AB consumption were collected from 2017 to 2020, and the active compounds (ACs) were expressed as milligrams of AC/total kilogram of body weight (BW) produced. Each AC was classified into one of four categories according to the European Medicines Agency classification of ABs for prudent and responsible use in animals: Avoid, Restrict, Caution, and Prudence. Data regarding the ACs in each category were analyzed using a linear model that included production phase, PRRS status, and their interaction as factors. Performance parameters, average age of the pigs at the end of each phase, daily live weight gain, feed-to-gain ratio, total losses, cost index, and medication costs were significantly influenced by the PRRS chain. The use of class B ABs was not affected by production phase or PRRS status. Conversely, for class C ABs, interaction between the two factors (p = 0.02) was observed; W/PRRS+ and F/PRRS+ showed the greatest AB use for this class (p = 0.003). For class D ABs, the interaction was significant (p = 0.01); class C and D ABs were used more in the weaning (p = 0.07) than in the fattening phase (p = 0.003). For the weaning phase, the use of class C and D ABs was greater in the PRRS+ than in the PRRS– chain (p < 0.01). In conclusion, PRRS status affected the growth of pigs and economic performance. Moreover, PRRS status significantly influenced the use of ABs during all the growing periods with the greatest impact being on the weaning phase.

Effect of antibiotic treatment on Mycoplasma hyopneumoniae detection and infectious potential

Mycoplasma hyopneumoniae (M. hyopneumoniae) causes significant economic losses in the swine industry. Antibiotics with activity against Mycoplasma spp. are employed for disease mitigation and pathogen elimination. However, veterinarians are often challenged with the detection of M. hyopneumoniae by PCR after antibiotic treatment, thus raising the question whether the bacterium is still infectious. The objective of this study was to evaluate the effect of tulathromycin treatment on M. hyopneumoniae detection and infectious potential during the acute and chronic phases of infection. For each infection phase, one age-matched naïve gilt was placed in contact with one M. hyopneumoniae infected gilt that was either treated with tulathromycin, treated and vaccinated, or non-treated, for 14 days. Four replicates per treatment group were performed for each infection phase. A numerical reduction in relative bacterial load was observed in acutely treated gilts compared to non-treated gilts. The rate at which naïve gilts became infected with M. hyopneumoniae was numerically reduced when co-housed with treated, acutely infected gilts compared to those housed with non-treated, infected gilts. During the chronic infection phase, M. hyopneumoniae was detected by PCR in more than 50 % of treated infected gilts and persisted for up to three months post-treatment. Transmission was not detected in all treatment groups however, the possibility that the pathogen was infectious could not be completely ruled out. Further research focused on assessing M. hyopneumoniae detection and viability post-treatment is necessary to guide control and elimination efforts.

Effect of Ethanolic Caesalpinia sappan Fraction on In Vitro Antiviral Activity against Porcine Reproductive and Respiratory Syndrome Virus

Porcine reproductive and respiratory syndrome virus (PRRSV) is a major epidemic in pig production, leading to economic losses in the pig industry worldwide. The use of medicinal plants with antiviral properties might be useful help to prevent and control PRRSV outbreaks. Caesalpinia sappan (CS) heartwood is an important herbal ingredient used in Thai folk medicine, possessing various biological activities, including antiviral activity. The present study focuses on the in vitro antiviral activity against PRRSV of a semi-purified fraction of ethanolic CS crude extract using preparative high-performance liquid chromatography. Qualification of the fractions illustrating positive antiviral activity was carried out with liquid chromatography–quadrupole time-of-flight mass spectrometry. The preparative chromatography separated the crude extract into six consecutive fractions, among which the first fraction showed potential antiviral activity by inhibiting PRRSV replication in a MARC-145 monolayer (virus titer 2.75 median tissue culture infective dose (TCID₅₀)/mL (log₁₀) vs. 9.50 median log10 TCID₅₀/mL of the control) at 72 h post-infection, and this fraction included byakangelicin, brazilin, naringenin, and brazilein. These results provide useful information for further study to effectively develop the CS bioactive antiviral compounds against PRRSV as a feed additive or veterinary drug in the pig industry.

Effects of PRRSV Infection on the Porcine Thymus

Porcine reproductive and respiratory syndrome virus (PRRSV) dramatically affects the thymus and its ability to carry out its normal functions. In particular, infection incapacitates PRRSV-susceptible CD14^pos antigen-presenting cells (APCs) in the thymus and throughout the body. PRRSV-induced autophagy in thymic epithelial cells modulates the development of T cells, and PRRSV-induced apoptosis in CD4^posCD8^pos thymocytes modulates cellular immunity against PRRSV and other pathogens. Pigs are less able to resist and/or eliminate secondary infectious agents due the effect of PRRSV on the thymus, and this susceptibility phenomenon is long recognized as a primary characteristic of PRRSV infection.