罗非鱼无乳链球菌病的研究进展

Research on Streptococcus agalactiae disease in tilapia: a review

无乳链球菌Streptococcus agalactiae作为罗非鱼Tilapia的主要病原菌,因其传染性强、致死率高,给罗非鱼养殖产业带来巨大的经济损失。无乳链球菌可通过多种途径感染罗非鱼,不仅能在宿主血液内增殖,随巨噬细胞在体内游走、侵染其他组织,还可透过血-脑屏障,侵入脑组织,导致罗非鱼呈现典型的临床症状和组织病理学变化。无乳链球菌的检测方法有多种,基于分子生物学的技术手段被广泛运用,通过分子分型的方法可获得菌株分子遗传多样性信息,有助于解析菌株的流行和传播规律。目前,抗菌药物仍是防控该病的首选,但长期用药和滥用药会加快菌株产生耐药性,疫苗是防控无乳链球菌病的有效途径,但适合大规模商业化应用的疫苗较少。本研究中全面归纳了罗非鱼无乳链球菌的病原学、流行病学、病理学、致病机制、检测方法、分子分型、耐药性及疫苗等方面最新研究进展,并提出存在急需解决的问题,旨在为防控罗非鱼无乳链球菌病提供参考资料。

Streptococcus agalactiae as one pathogen in tilapia has brought huge economic losses to the tilapia breeding industry due to strong contagiousness and high mortality by the pathogen.This pathogen infects tilapia by different pathways,including cohabitation,oral route,immersion,intraperitoneal and intramuscular inoculation,and is capable of replicating in tilapia bloodstream,penetrating the blood-brain barrier into brain,resulting in meningitis,and passing through the mucus layer of both the stomach and intestine and finally adhered,colonized and invaded the gastrointestinal epithelium,leading to typical histopathological changes,including meningitis,epicarditis,hemorrhage in renal interstitium,multifocal necrotizing splenitis and septicemia in tilapia.The most frequent clinical symptoms of affected tilapia are erratic swimming,exophthalmia,hemorrhage at the operculum,pectoral,and ventral areas and rapidly progressing mortality.Traditional diagnosis methods for the detection of S.agalactiae in the host tissues are based on bacterial culture,and DNA-based methods including PCR and loop-mediated isothermal amplification are increasingly used.Molecular typing of S.agalactiae strains has been performed by different methods,such as molecular serotyping,amplified fragment length polymorphism,multiple-locus variant-repeat assay,and pulsed field gel electrophoresis,multilocus sequence typing.Virulence genes have faster mutation rates and higher polymorphism than housekeeping genes,and the multi-virulence locus sequencing typing method can be widely used to evaluate genetic variation in S.agalactiae.At present,aquaculture depends on antibiotics to treat or prevent S.agalactiae disease in tilapia.Although these antimicrobials have some benefits,the abuse of antibiotics occurs during tilapia production,leading to the development of antimicrobial-resistant strains.Although vaccination is an alternative method to control streptococcal diseases,few commercial vaccines are currently available for treatment of S.agalactiae disease in a large scale tilapia production.This paper comprehensively summarizes the latest research progress and development trends in etiology,epidemiology,pathology,pathogenic mechanism,detection methods,molecular typing,antibiotic resistance and vaccines of S.agalactiae in tilapia.The current problems that need to be solved are discussed and valuable measurements are suggested for the prevention and control of S.agalactiae disease in tilapia.