Epidemiological Investigation And Susceptibility Analysis Of Vibrio Parahaemolyticus In Shrimp In Qingdao

Vibrio parahaemolyticus is a gram-negative pathogen that widely exists in aquaculture environments.In recent years,the detection rate of Vibrio parahaemolyticus is relatively high in aquaculture animals in parts of northern China.It can infect a variety of aquatic animals,such as fish,shellfish,shrimp and crabs,and is one of the main pathogens of aquatic animals.In addition,it can also infect humans and cause high fever,watery diarrhea,vomiting,gastrointestinal cramps and other clinical symptoms,which can lead to dehydration and even death in severe cases.It poses a serious threat to aquaculture and human health.To analyze the infection status and epidemiological characteristics of Vibrio parahaemolyticus(V.parahaemolyticus)in shrimp culture in some coastal areas of Qingdao,and to explore the influencing factors,so as to provide evidence and improvement measures for the prevention and control of V.parahaemolyticus infection.A total of 25 strains of Vibrio parahaemolyticus were isolated from 121 fish farms in the coastal areas near Qingdao.Virulence gene detection and multilocus sequence typing were carried out.Epidemiological methods were used to analyze the correlation between current feeding patterns,environmental hygiene,management conditions and Vibrio parahaemolyticus infection.Key findings were as follows:1.This study collected water samples and shrimp samples from 121 aquaculture farms in the coastal areas near Qingdao from 2021 to 2022.A total of 25 strains of Vibrio parahaemolyticus were identified by routine bacterial isolation and identification,16 Sr DNA and other methods,with a detection rate of 20.66%.The results showed that the prevalence of Vibrio parahaemolyticus in aquatic animals was serious in the coastal area of Qingdao.2.The main virulence genes tlh,tdh and trh of Vibrio parahaemolyticus were further detected by common PCR in the isolated 25 strains,of which 25 strains(100%)carried tlh gene,2 strains(8%)carried trh gene,and 0 strains(0%)carried tdh gene.The results indicated that the Vibrio parahaemolyticus isolated in this study was weak in pathogenicity.At the same time,the virulence genes pir A and pir B that cause shrimp hepatopancreatic necrosis were detected,and the results showed that 4 strains carried the virulence genes that cause shrimp hepatopancreatic necrosis,and the carrying rate was 16%.These results indicate that Vibrio parahaemolyticus carrying these two genes plays an important role in causing shrimp hepatopancreatic necrosis.3.MLST analysis was performed on 25 Vibrio parahaemolyticus isolates using seven specific housekeeping genes.The results showed that 24 strains were successfully matched to 14 related ST types.There were 4 ST1160(16.6%),4 ST2621(16.6%),3 ST2603(12.5%),2 ST114(8.3%).Among them,ST1160 and ST2621 had higher isolation rates.ST1160 was isolated from Jimo District and Laoshan District of Qingdao City,ST2621 was isolated from Jimo District and Huangdao District of Qingdao City,ST114 was isolated from Huangdao District and Jimo District of Qingdao City,and there was inter-regional transmission.The 14 ST types included 14 monomers,with rich genetic diversity.No homologous complex was produced,but some regional cross-transmission occurred.4.The information related to the susceptibility factors of Vibrio parahaemolyticus in 121 farms was collected,and the positive rate of bacterial isolation and identification was combined with univariate and multivariate logistic regression analysis.The results showed that sewage backflow and regular pond disinfection were the main risk factors for the susceptibility to Vibrio parahaemolyticus.The risk analysis showed that the field group with sewage backflow(OR = 13.00,95%CI:4.06-41.54)and ponds without regular disinfection(OR = 11.70,95%CI: 3.21-42.69)had a significantly increased risk of being infected with V.parahaemolyticus.Other factors,such as whether the breeding site is in good condition,external vehicle access,and dog breeding on the farm,were statistically significant in the univariate regression analysis,and these factors were closely related to the occurrence of Vibrio parahaemolyticus infection,which should be paid attention to in the process of breeding.