Developing a 'validation portfolio' to exploit key virulence proteins in Fasciola species for parasite control

热带肝吸虫寄生虫是亚洲和非洲最重要的家畜寄生虫之一。这种疾病造成了非常大的损失，特别是在印度的牲畜中，一些地区的感染率高达55%。最近估计，印度每年因家畜感染肝吸虫而造成的损失在19.5亿美元至47.8亿美元之间。这对以农业为主的印度经济是一个巨大的负担，并直接影响到大小农场的生产率，对个体农民及其家庭产生负面影响。感染肝吸虫的水牛在一般健康、增重、饲料转化效率和繁殖力方面都有下降。感染性蠕虫阶段包裹在植被上，以至于宿主动物在放牧过程中无意中吃掉了包囊。幼虫一旦进入肠道，就会孵化，穿过肠壁，穿过肝脏，最终成为胆管中的成虫，在那里它们以宿主血液为食，大大降低了动物的健康，并极大地降低了农业生产率。在发达国家，肝吸虫病的防治主要使用化学药物三氯苯达唑(TCBZ)。这种药物是肝吸虫控制的致命弱点，因为它是唯一既能杀死成虫又能杀死致病幼虫的药物。随着寄生虫种群对驱虫剂的耐药性在全球蔓延，迫切需要新的控制战略，而发展中国家许多地区的农业社区根本负担不起以驱虫剂为基础的短期治疗选择。因此，迫切需要制定一种基于疫苗接种的具有成本效益的单一治疗控制策略。许多疫苗试验已经在肝吸虫中完成，其中许多显示出一些成功，但没有一种疫苗提供足以立即商业化的保护水平。问题是，由于大多数领先的候选疫苗存在于寄生虫内相关的大型蛋白质组中，因此无法确定该组中的哪一个是最佳候选，因此到目前为止，这些决定还没有经过严格的验证。为此，印度和英国实验室之间的这个国际合作项目将首次纳入新的快速吞吐核苷酸和蛋白质技术，以验证候选蛋白质，从而评估这些领先的候选疫苗是否可以用于治疗世界不同地区的肝吸虫寄生虫，这是成功商业生产的关键。一旦疫苗靶标被证实广泛存在于肝吸虫种群中，我们将使用另一种名为反向遗传学的新技术，该技术可以关闭(或沉默)寄生虫中的靶标，然后确认该靶标是否对寄生虫的生存至关重要。如果被证实对寄生虫的生存很重要，我们随后将使用酵母实验室培养物来生产候选疫苗，用于在印度的牲畜身上进行疫苗试验。由于这是一个多学科、多实验室的项目，我们成立了一个国际科学咨询委员会(ISAB)，以管理和协调进展并排除故障。ISAB的成员包括一名来自大型动物制药公司的代表、一名具有多年工业经验的寄生虫学家、一名领先的肝吸虫疫苗接种世界权威以及一名来自印度工业生物技术部门的代表。该方案涉及BBSRC的使命，包括牲畜疾病的治疗、新技术的应用和国际合作。来自该项目的经过验证的试验疫苗(S)将为治疗肝吸虫病的商业开发奠定基础，我们的技术策略可以直接转移到动物和人类的其他蠕虫寄生虫上。

The tropical liver fluke parasite Fasciola gigantica is one of the most important worm infections of livestock in Asia and Africa. The disease inflicts very significant losses especially in livestock in India, with infection levels reaching 55% in some regions. Recently-estimated costs for liver fluke induced losses associated with livestock in India fall within the range of US$1.95-4.78 billion per year. This is a huge burden to the largely agricultural Indian economy and directly impacts the productivity of large and small farm holdings alike, negatively impacting individual farmers and their families. Liver fluke infected buffalo show reduction in general health, weight gain, feed conversion efficiency and reproduction. The infective worm stage encysts on vegetation such that host animals inadvertently consume the cysts during grazing. Once in the gut, the juvenile worms hatch, burrow through the gut wall and penetrate the liver, ending up as adult worms in bile ducts where they feed on host blood, significantly diminishing the health of the animal and greatly reducing agricultural productivity. In the developed world liver fluke is mainly controlled using the chemical triclabendazole (TCBZ). This drug is an Achilles heel of liver fluke control as it is the only drug that kills both adult and pathogenic juveniles. New control strategies are urgently needed as anthelmintic resistance in parasitic worm populations is spreading globally, and agricultural communities in many parts of the developing world simply cannot afford short-lived, anthelmintic-based treatment options. Therefore, there is an urgent need to develop a cost effective, single-treatment control strategy based on vaccination. Numerous vaccine trials have been completed in liver fluke, many showing some success, but none have provided protection levels adequate for immediate commercialization. The problem is that since most leading vaccine candidates exist in large, related groups of proteins within parasites, it has been impossible to determine which is the best candidate from the group such that up until now, these decisions have not been subject to rigorous validation. To this end, this international collaborative project between laboratories in India and the UK will, for the first time, incorporate new fast throughput nucleotide and protein technologies to validate the candidate proteins and thereby assess if these leading vaccine candidates can be used to treat liver fluke parasites in different parts of the world, a key to successful commercial production. Once a vaccine target is confirmed as widely present in liver fluke populations, we will use another new technology called reverse genetics that can switch-off (or silence) a target in a parasite, and then confirm if this target is essential for parasite survival. If confirmed as important to parasite survival, we will subsequently use yeast laboratory cultures to produce the candidates for vaccine trials in livestock in India. Since this is a multi-discipline and multi-laboratory project, we have formed an International Science Advisory Board (ISAB) in order to manage and co-ordinate progress and to trouble-shoot. Members of the ISAB include a representative from a large Animal Pharmaceutical Company, a parasitologist with many years of industrial experience, a leading world authority on liver fluke vaccination and a representative from the industrial Biotechnology sector in India. The programme addresses the mission of the BBSRC, including treatment of diseases of livestock, application of new technologies and international collaboration. Validated trial vaccine(s) from this programme would form the basis for commercial development for treating liver fluke disease, and our technology strategy is directly transferable to other helminth parasites of animal and humans.