Histopathology Of The Headkidney In Tilapia Infected By Streptococcus Agalactiae

Tilapia,currently the third most important aquaculture fish species in the world.Tilapia cultivation systems are expected to account for about 60%of the total aquaculture production by 2025.Unfortunately,Group B Streptococcus(GBS),a bacterial pathogen,has considerably damaged tilapia farming in recent years,where controlling and purification is urgent needed for III classic of aquatic animal disease.At present,research on GBS disease has drew enough attention in clinical application and made certain progress,while the fundamental reseaech remains poor.Fish headkidney,a site of invasive GBS infections,is an essential immune organ with important hematopoietic function in fish,GBS cause tilapia headkidney pathological damage rarely reported.In the study,twenty(250±10)g healthy tilapias were chosen formorphology?histology and ultrastructural structure observation;eighty tilapias were randomly divided into five group,Infected GIFT tilapias with 1.0×10~7cfu GBS.Headkidney was sampled at 0?4?8?24 and 72h during the infected time to analyzed general pathology and histopathology of headkidney,and the dynamic distribution of GBS.we used light and electron microscopes,immunohistochemical staining and flow cytometry(FCM)techniques.Research results are as follows:1:Tilapia headkidney is located in the heart abdominal diaphragm back ahead,about two,there is no nephron in adult fish head kidney tissues,histologically,headkidney can be divided into two areas:the central and peripheral zone,central region was made up of lymphoid tissue and blood sinus,containing melanin macrophages center(MMCs),lymphoid tissue arranged in funicular,around the blood vessels in the radial distribution,lymphatic line is separated by blood sinus,peripheral area is characterized by diffuse lymphoid tissue,blood sinus also less and smaller.In a word,tilapia hesdkidney is a typical hematopoietic lymphoid tissue.2:After tilapia infection with GBS,the dynamic pathological changes mainly embodied in the internal organs hyperemia,bleeding,swelling,corneal opacity and softening of the brain,head kidney was mainly reflected in color and head kidney index,0-4 h,color was dark,4-24 h,obvious swelling and dark,show different degrees of purplish red,24-72h,head kidney enlargement and the color darkened degree is lighter than 4-24h,but it is still swollen and the color darkened;head kidney index,0-4h,remarkably significant increased,8-24 h,significantly increase,24-72 h,remarkably significant increased;dynamic histopathological changes of the head kidney,4-8h,melanin macrophages center number decreased significantly,smaller,less components,coloring shallow,loose structure,artery endothelial cell loss,inflammatory cells began to appear;8-24h,melanin macrophages center quantity is reduced or even disappeared,only a small amount of brown granules,endothelial cell swelling,fall off,mesolamella smooth muscle degeneration,necrosis,internal membrane,the mesolamella,the outer membrane layers were edema and inflammatory cell infiltration,disorganized lymph and blood sinus congestion,increased vascular permeability,appear homogeneous red dye perivascular inflammatory exudate and inflammatory cells,24 h,head kidney inside clouds gathered a large number of GBS,GBS had capsule and survived in lymphocytes,macrophages and red blood cells.24-72h,a huge increase in melanin macrophages center,small volume,ingredients disappeared,not the brown or black particles,structure loose in vacuoles,interstitial group that article into a boundary is not clear without red dye material structure,lymphocytes and macrophages decreased,congestion is serious,the melanin macrophages central necrosis,see a lot of dead zone.The main dynamic pathological cells changes as follows:0-24h,the number of living cells had no significant difference;however,during 24-72h,a significant decline in living cells,cells apoptosis and necrosis in tissue.4-8h,GBS significantly increased,24-72h,GBS remarkably significant increased.Combined with the typical dynamic pathological changes and the content of GBS,tilapias that were infected with 1.0×10~7 cfu GBS,headkidney suffered from acute bacterial suppurative inflammation,which was divided into 3 period,in reaction period(0-4h):generally normal,head kidney volume index increases,melanin macrophages center and blood vessels are normal,no GBS,no dead zone;in slowing phase period(4-8h):generally normal,head kidney index increased significantly,macrophages center and lymphocytes reduce melanin,head of renal vascular injury,the organization began to appear a small amount of GBS,no dead zone.In peril period(8-24h):the typical symptoms of fish,head kidney index increased significantly,macrophages center and lymphocytes reduce melanin,head kidney blood sinus in a large number of red blood cells,blood filling,there are a large number of inflammatory exudation and GBS,no dead zone;in peril period(24-72h):the typical symptoms of fish,head kidney index increased significantly,the melanin macrophages center,congestion,there is a lot of GBS,with necrotic area.In conclusion:the headkidney structure and function were damaged seriously after GBS infection,which the excessive inflammation might be an important cause for facilitate acute death.