Etiological Screening Of Hepatopancreatic Necrosis In Eriocheir Sinensis And Analysis Of The Possible Mechanism Of Avermectin-induced Pathogenesis

In order to investigate the pathogenesis and regularity of hepatopancreatic necrosis of Eriocheir sinensis,establish the disease model and determine the clinical diagnostic criteria the disease.This experiment starts with an epidemiological investigation.By visited the affected ponds,asked about the breeding and disaster situation of the affected farmers.A total of more than 60 questionnaires were completed,and 80 naturally occurring crabs suspected of hepatopancreas necrosis disease were collected.Among them,12 crabs with typical clinical symptoms and different degrees of pathological changes were selected to form the natural disease crab group.Code these 12 naturally ill crabs as No.1 ~12.And then,white spot syndrome virus and microsporidium in hepatopancreas and muscle were detected by PCR.The results of an epidemiological survey showed that Xinghua City,Jiangsu Province,was the main epidemic area of hepatopancreatic necrosis disease,2015 and 2016 were the worst,2015 was the peak of the outbreak,and only a slight decrease in the incidence in 2016.However,it still caused huge losses to the farmers.In 2017,it was obviously improved and the incidence of the disease was greatly reduced.The results of pathogen detection showed that the positive rate of microsporidium in the hepatopancreas and muscles of the sick crab was 33.3% and 0.Because the proportion was low,the possibility of microsporidium as hepatopancreas necrosis was less,and the microsporidium infection might be secondary to microsporidium.The detection rate of WSSV in hepatopancreas and muscles was 90%,but it did not show the symptom of white spot syndrome.Indicating that the virus concentration in the sick crab did not reach the minimum concentration required for the occurrence of the disease symptom,although it contained WSSV.Therefore,it is more likely to judge the sick crab as a carrier of WSSV,while WSSV is less likely to be the pathogen of hepatopancreatic necrosis disease.The epidemiological survey found that in 2015 and 2016,all river crab farmers in the investigated areas carried out insecticidal activities at the end of April and early May.After mid-May of the same year,the number of hepatopancreatic necrotic disease crabs began to increase significantly.The outbreak of the disease occurred on a large scale in June and July,so it sames that the outbreak of the disease is related to the time of application of the drug,so it is determined that the insecticidal drugs is the research direction of the disease.After pre-test screening of insecticidal drugs,the results of formal experiments showed that the hepatopancreas of healthy Eriocheir sinensis could be induced by semistatic method under the condition of abamectin concentration of 8μg/L in the water environment,and the hepatopancreas could be changed to hepatopancreas enlargement,some liver tubules albinism,all liver tubules albinism,hepatopancreas necrosis,abdominal cavity hydronephrosis,branchial filaments color darkening symptom,through comparison with the natural disease crabs,the symptoms are similar.The similarity between the induced group and the natural group was further studied from the histopathological point of view.It was found that the histopathological symptoms of hepatopancreas and muscles of the two groups had high similarity in the same symptom stage.According to the pathological symptoms of the hepatic tubule.The complete pathogenesis of hepatopancreatic necrosis disease was divided into four stages,which were named hepatopancreas hyperplasia stage,partial hepatic tubule albinism stage,hepatic tubule complete albinism stage and hepatopancreatic necrosis stage.However,the Gill tissue was strongly affected by the living environment and water quality,and the induction group showed periodic changes.No Gill health was found in the first three stages,and edema and hyperemia appeared in the hepatopancreatic necrotic phase.In the natural group,the crab was collected from different ponds,so the branchial symptoms showed distinct individual differences,such as edema,hyperemia,epithelial cell fusion of branchial lobules,and so on.The activity of lactate dehydrogenase(LDH),)acetylcholinesterase(AChE),glutathione S-transferase(GSTs),superoxide dismutase(SOD),catalase(CAT)in the hepatopancreas of two groups of sick crabs was determined and compared at different symptom stages.The results showed that with the aggravation of hepatopancreas,the changes of hepatopancreas enzyme activities in the induced group and the natural group remained the same,in which the activities of lactate dehydrogenase and acetylcholinesterase continued to decrease,while the activities of the glutathione Stransferase(GSH-S-transferase),superoxide dismutase(SOD)and catalase(CAT)increased first and then decreased.Finally,the pathogenesis of hepatopancreatic necrosis disease carbs was summarized.The mechanism and relations between hepatopancreas enlargement,muscular atrophy and hydroperitoneum were discussed.