Effect of co-infections on the pathogenesis of the most important swine viruses

正在研究猪病毒，但主要是在单一感染的情况下。不幸的是，这种类型的调查并不代表真实的生活情况。事实上，几种病原体在一只动物身上混合在一起，大大降低了病原体特异性治疗（如疫苗接种和抗生素控制细菌继发感染）的效率，并使预防措施更加难以实施。事实上，呼吸道中多种病原体的联合构成了已知的猪呼吸道疾病复合体。该复合体中包括几种病原体，例如猪圆环病毒2型（PCV 2）、猪繁殖与呼吸综合征（PRRS）病毒（PRRSV）和猪流感病毒（SI）。猪通常是几种病原体的携带者，因此调查合并感染是了解结果和如何治疗传染病的一个合乎逻辑的步骤。就全世界养猪业的经济损失而言，最重要的动物疾病是PRRS（加拿大每年的经济损失为1.5亿美元）。在上一次断奶后多系统衰竭综合征（PMWS）爆发期间，魁北克猪群每年有20万头猪死亡。另一种主要疾病是猪流感。它在加拿大猪群中高度流行，在猪生产中造成约2.5%的死亡率。PRRS、PMWS和猪流感传染性病毒病的病原体分别是PRRSV、PCV 2和SI。本研究计划的主要目标是进一步表征猪共感染发病机制，并在细胞水平上更好地理解为什么在某些情况下存在拮抗作用（这可能导致我们发现新的抗病毒药物），而在其他情况下，在共感染期间猪病原体之间存在协同作用。为了帮助我们研究猪的合并感染，最近对新的病毒容许细胞系进行了遗传修饰，使其对一种以上的猪病毒具有容许性。因此，本五年研究计划的主要目标是研究PRRSV、PCV 2和SI以各种组合共感染（使用每种病毒的几种基因型）的发病机制，以更好地理解可能参与病毒促进和/或抑制的宿主反应。在体外共感染实验期间将研究几个参数，例如：病毒复制动力学、细胞周期/细胞死亡（荧光显微镜检查、酶测定等），细胞因子（qPCR，ELISA）和细胞途径调节（抗体微阵列，westernblot）。总之，对猪混合感染的研究将使我们在更现实的现场条件下更好地了解猪病毒的发病机制，并随后将导致具有高应用潜力的新发现，用于控制和治疗猪病毒性传染病。

Swine viruses are being investigated but predominantly in a context of single infections. Unfortunately, this type of investigations do not represent real life situation. In reality, several pathogens commingle together in a single animal reducing dramatically the efficiency of pathogens-specific treatments (such as vaccination and antibiotics to control bacterial secondary infections) and making it more difficult to implement prophylactic measures. In fact, associations of multiple infectious agents in the respiratory tract constitute what is known to be the porcine respiratory diseases complex. Several pathogens are included in that complex such as porcine circovirus type 2 (PCV2), porcine reproductive and respiratory syndrome (PRRS) virus (PRRSV), and swine influenza virus (SI). Swine are often carriers of several pathogens, making the investigation of co-infections a logical step to understand the outcome and how to treat infectious diseases. The most important animal disease, in term of economical loss in swine industry worldwide, is PRRS (150 million $/year of economic losses in Canada). During the last postweaning multisystemic wasting syndrome (PMWS) outbreak, 200,000 pigs/years died in Quebec swine herds. Another major disease is swine flu. It is highly prevalent in Canadian swine herd and it causes a mortality of around 2.5% in swine productions. The etiological agents involved in PRRS, PMWS and swine flu infectious viral diseases are PRRSV, PCV2 and SI, respectively. The main goal of the present research program is to further characterize the mechanisms involved in the pathogenesis of co-infections in swine and to better understand at a cellular level why there is in some instance an antagonism (which could lead us to the discovery of new antiviral drugs) and in other instance a synergy between swine pathogens during co-infections. To help us to investigate swine co-infections, new virus permissive cell lines were recently genetically modified to render them permissive to more than one swine virus. Thus, the main objective of the present five years research program is to investigate the pathogenesis of PRRSV, PCV2 and SI co-infections (using several genotypes of each virus) in various combinations, to better understand the host responses that could be involved in virus promotion and/or inhibition. Several parameters will be studied during the in vitro co-infections experiments such as: virus replication kinetics, cell cycle/cell death (fluorescent microscopy, enzymatic assays, etc.), cytokines (qPCR, ELISA), and cellular pathways modulation (antibody microarray, westernblot). In conclusion, the study of swine co-infections will give us a better understanding of the swine viral pathogenesis in a more realistic field condition and subsequently will lead to new discoveries with high applied potential for the control and treatment of swine viral infectious diseases.