Protecting Pigs From Enzootic Pneumonia: Rational Design Of Safe Attenuated Vaccines.

猪肺炎支原体（Mycoplasma hyopropionia，M.hyop）是引起猪流行性肺炎（EZOP）的主要病原。感染在世界范围内发生，并给养猪业造成重大经济损失，从而对养猪户产生重大的社会经济影响。感染猪与易感猪之间的密切接触是猪肺炎支原体传播的主要途径。认为仔猪出生时无猪肺炎支原体，因为未记录宫内传播，首次暴露事件发生在哺乳期，此时仔猪与脱落微生物的母体接触。事实上，哺乳期的长度已被认为是断奶前仔猪感染猪肺炎支原体的一个风险因素，鉴于猪肺炎支原体的流行率约为30%，这使仔猪面临巨大的感染风险。不幸的是，目前还没有商业疫苗可以预防这种初始感染。事实上，断奶时猪肺炎支原体的仔猪定殖在隔离生产系统中特别重要，在隔离生产系统中，猪被转移到清洁设施中进行生长和肥育阶段。有人提出，猪肺炎支原体最初的群体定殖决定了下游的临床表现和疾病严重程度，这进一步受到猪肺炎支原体感染的长期影响，可长达240天，以及即使在风传播后也具有感染性的能力（距离受感染的农场远达9.2公里）。因此，通过有效的疫苗中断定殖周期将有利于整个猪生产系统。猪肺炎支原体主要存在于气管、支气管和细支气管的粘膜表面，在粘附过程中涉及不同的粘附素和脂蛋白，从而使受感染的动物更容易继发感染。具体而言，粘膜纤毛器的破坏以及猪肺炎支原体模块化免疫应答的能力增强了感染猪对继发病原体的易感性。虽然猪肺炎支原体仍然对各种抗生素敏感，但需要减少抗生素的使用，以避免出现多重耐药菌株以及减少抗菌药物使用的一般驱动力。目前可用的疫苗通常具有成本效益，但主要由灭活疫苗组成，灭活疫苗改善了生产参数，但不能防止病原体的感染或传播，并且它们的使用通常限于一个年龄组，即3周龄后的母猪或仔猪。因此，优先研究开发具有保护性免疫力和减少传播的新疫苗，以及优化从猪群中消除猪肺炎支原体的方案。在这里，我们的目标是生产不能在猪身上引起疾病但仍能刺激保护性免疫反应的细菌菌株。这项工作建立在先前BBSRC资助的工作基础上，确定了猪中病原体生存所必需的基因，以及AHDB资助的从英国猪中分离细菌菌株的工作。一旦完成，该项目将发现疾病所必需的细菌基因，作为开发更好疫苗的基础，以预防地方性肺炎的传播。

Mycoplasma hyopneumonia (M.hyop) is the primary pathogen of enzootic pneumonia (EP), a chronic respiratory disease in pigs. Infections occur worldwide and cause major economic losses to the pig industry, thus having a significant socio-economic impact on pig farmers. Close contact between infected and susceptible pigs is the main route of M.hyop transmission. Piglets are considered free from M.hyop at birth, as in utero transmission has not been documented, and first exposure events occur during the lactation period, when piglets are in contact with dams shedding the microorganism. In fact, the length of the lactation period has been suggested as one risk factor for piglet colonization with M.hyop prior to weaning, and given that the prevalence of M.hyop is around 30%, this places piglets under an enormous risk to be infected. Unfortunately, there are currently no commercial vaccines available that would prevent this initial infection. Indeed, piglet colonization with M.hyop at weaning age is of special importance in segregated production systems, where pigs are transferred to clean facilities for the growing and finishing phases. It has been proposed that the initial group colonisation with M.Hyop determines downstream clinical presentation and disease severity, which is further impacted by the long duration of M.hyop infection that can reach up to 240 days as well as the ability to be infective even after wind dispersal (as far as 9.2km from an infected farm). Thus, an interruption of the colonisation cycle through effective vaccines will benefit the whole porcine production system. M.hyop is primarily found on the mucosal surface of the trachea, bronchi and bronchioles, with different adhesins and lipoproteins being involved in the adherence process, thus rendering infected animals more susceptible to secondary infections. Specifically, the destruction of the mucociliary apparatus, together with the ability of M.hyop to module the immune response, enhances the susceptibility of infected pigs to secondary pathogens. Whereas M.hyop is still susceptible to a variety of antibiotics, their use needs to be reduced to avoid occurrence of multi-drug resistant strains as well as the general drive to reduce antimicrobial usage. Current available vaccines are often cost-efficient but mainly consist of inactivated vaccines which improve production parameters but do not prevent infection or spread of the pathogen, and their use is often limited to one age group, i.e. sows or piglets after 3 weeks of age. Thus, research on developing new vaccines that confer protective immunity and reduce transmission is a priority, as well as optimization of protocols to eliminate M.hyop from pig herds. Here, we are aiming to produce strains of bacteria which are unable to cause disease in pigs but still stimulate a protective immune response. This work builds on previous BBSRC-funded work identifying genes which are essential for survival of the pathogen in pigs and AHDB funded work to isolate strains of bacteria from UK pigs. Once complete, the project will have discovered bacterial genes that are necessary for disease as a basis for the development of better vaccines to prevent, and prevent the circulation of, enzootic pneumonia.