| Haemophilusparasuis(Hps),is an infectious disease caused by Haemophilus Parasuis(Hps)infection in pigs,characterized by multiple serositis,arthritis,dyspnea and high fever.Hps is a opportunistic pathogen,often mixed with other diseases.The infection is usually chronic,which seriously affects the growth performance of pigs and brings huge economic losses to pig industry.For a long time,antibiotics have been effective drugs for the prevention and treatment of Hps.However,drug-resistant strains of Hps are increasing nowadays,and its effect is declining due to the clinical non-standard use and other factors.In China,the drug resistance rate of Hps and the minimum inhibitory concentration of Hps drugs to the pathogen showed an overall increasing trend,and multiple drug resistant strains appeared,and the drug resistance was more serious.Based on the infection hazard of this disease and the decrease of antibiotic control effect caused by the increase of Hps resistant strains,drug sensitivity test was performed with 571 Hps Guizhou strain which has been isolated and identified from 2013to 2019 in this study.The results can not only reveal the current situation of drug resistance of Hps epidemic strains in Guizhou,but also can provide some theoretical basis for the evolution of Hps resistance and clinical medication.Moreover,in consideration of the hazards of Hps pathogen chronic infection,we replicated Hps single chronic infection cases to explore the effects of Hps pathogen infection on the growth performance of piglets aged 30 to 75 days,in order to provide some reference for clinical diagnosis and comprehensive prevention and control of Hps.1.Drug resistance analysis of Hps guizhou strainThe drug resistance rates of 571 Hps strains isolated and identified from 152 pig farms in 9regions,27 counties and 152 pig farms in Guizhou province from 2013 to 2019,were observed by drug sensitivity test,and the status of drug resistance and evolution trend of Hps strains were statistically analyzed.The results were showed as follows:(1)The drug resistance rates of 571 Hps strains in Guizhou province was significant different within 15 commonly used antibiotics used in this study(P < 0.05),ranging from 14.36% to 70.58%;The drug resistance rates to sulfamethoxine sodium(70.58%)and oxytetracycline(68.12%)were significantly higher than those of the other 13 antibiotics.(2)There were regional differences in drug resistance rates of Hps isolates to the same antibiotic in 9 regions,among which the regional difference was the largest in the drug resistance rate to ceftiofur;the drug resistance rate was the highest in Zunyi region,which was 3.97 times that of the lowest region(Qianxinan);the regional difference was the lowest in the drug resistance rate to penicillin,and its resistance rate was the highest in Tongren region,which was 1.09 times higher than that in Qiannan.(3)The interannual evolution of drug resistance of 571 Hps isolates was enhanced,among which ampramycin,gentamicin and temicorin showed an increasing trend year by year,and the interannual difference of ampramycin was the largest.○4 From 2013 to 2019,the drug resistance rates of571 Hps strains in Guizhou to both oxytetracycline and tetracycline decreased by 1.56%compared with 2013,while the interannual evolution of drug resistance rates to other 13 antibiotics showed an overall upward trend.Among these 15 antibiotics,the drug resistance rates of amprimycin,polymyxin,temicorin,doxycycline,cefuroxime,gentamicin,flubenicol and ofloxacin increased rapidly(increased by 17.58%-37.33% compared with 2013),while the drug resistance rate of sulfamethoxine sodium,penicillin,amoxicillin,streptomycin and enrofloxacin increased slowly(2.98%-5.25% higher than that of 2013).2.Determination of growth performance of piglets infected with Hps Guizhou strain Eighteen 30-day-old piglets with double negative Hps antigen and antibody,negative specific pathogens,were selected and divided into the experimental group and the control group(9piglets in each group).In the experimental group,Hps single infection cases were replicated to analyze the differences between the two groups and to explore the effects of Hps single infection on the growth performance of piglets.The results were showed as follows:(1)During the observation period(30 to 75 days of age),piglets in experimental group showed clinical symptoms such as lethargy,coarse coat,emaciation(prominent spine joints)and dyspnea.(2)Comparative analysis of the growth performance indexes in the two groups showed that: the average head gain(14.64±2.25kg)and the average daily gain(0.31±0.04kg)in experimental groups were significantly lower than those in control group(19.87±1.47 kg for average head gain and 0.44±0.03 kg for average daily gain),and that of the experimental group decreased 26.32% and 29.54%compared with control group,respectively.Compared with the control group,the average total feed in experimental groups was significantly decreased(13.27%),and the feed to meat ratio was significantly increased(25.66%),indicating that Hps single infection significantly affected the growth performance of piglets.(3)The pathological observation results of tissue and organs showed that the pathological changes of lymph node,lung and heart were observed in the experimental group,and the pathological sections of lung tissue showed obviously pathological changes.In summary,this study systematically analyzed and revealed the resistance of 571 Hps strains from 9 regions of Guizhou province to 15 commonly used drugs,and explored the effects of Hps on the growth performance of piglets through the comparative test of single chronic infection.According to the results of this study,the following conclusions can be drawn:(1)571 strains of Hps from 9 regions showed high drug resistance to 15 antibiotics overall in Guizhou province.There were significant differences among the drug resistance rates of 571 Hps Guizhou strains to different antibiotics,but there was no significant regional difference among the average drug resistance rates of 571 Hps strains to the same antibiotics in different regions.(2)From 2013 to 2019,the interannual evolution of drug resistance rates to oxytetracycline and tetracycline of 571 Hps strains in Guizhou showed an overall downward trend,while the interannual evolution of drug resistance rates to the other 13 antibiotics showed an overall upward trend,and their evolution of drug resistance was enhanced.(3)Chronic infection with Hps isolates in Guizhou can significantly reduce growth performance indexes of piglets,such as daily gain,feed to meat ratio and feed intake.(4)The single chronic infection of Hps Guizhou strains can cause pathological changes in lymph nodes,heart and lung organs of piglets,and resulted in pathological damage to lung tissue cells in different degrees. |
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