| Piglet diarrhea is a common and ingrained problem in the development of pig industry.Every year,the economic loss caused by piglet diarrhea is very huge.The causative agents of piglet diarrhea are complex due to various pathogens which are mainly composed of infectious and non-infectious factors.In particular,the virus and bacterial infection are more common.From 2016 to 2017,piglet diarrhea occurred in some large-scale farms in northern Xinjiang,the main symptoms of which were diarrhea,emaciation and dehydration,and the efficacy of antibiotic treatment and vaccine control were not satisfactory,which caused farmers' serious economic losses.In order to find out the main causes of piglet diarrhea in some areas of northern Xinjiang,seven large-scale farms in Shihezi,Karamay,Yili and Borle were selected as the research objects,in which the piglet diarrhea frequently occurred.First,the field epidemiological investigation was carried out to find out the possible source of transmission,route of transmission and predisposing factors,to observe the main clinical symptoms and pathological changes,and monitor the level of immune antibody in pigs.A total of 111 samples of small intestine and its contents were collected from piglets with diarrhea.PEDV,Po RV and TGEV were detected by RT-PCR method,which are the main causative agents of the viral diarrheaand homology analysis was carried out with commercial vaccine strains and epidemic strains.At the same time,routine microbiological methods and 16 s rRNA sequence analysis were used to isolate and identify bacterial pathogens(Escherichia coli).Drug sensitivity and infection test on mice were also conducted.Finally,the main pathogens and characteristics of piglet diarrhea in northern Xinjiang area were determined,which provided scientific basis for clinical treatment,prevention and control of piglet diarrhea in Northern Xinjiang area.The results are as follows:(1)Field epidemiological investigation of piglet diarrheaThe piglet diarrhea occurred mainly in winter and spring in the experimental area with a fast transmission speed.The transmission route included horizontal transmission between the same nest and vertical transmission between mothers and their offsprings.The highest morbidity and mortality fell in7-day-old piglets were,and the morbidity and mortality were up to 80%-90% in 2-month –old group.The ill piglets mainly showed watery diarrhea along with vomiting,dehydration,wasting and other symptoms.Pathological examination showed that the intestinal wall was thin and smi-translucent,the intestine was filled with thin yellow fluid,and part of the stomach was full with undigested milk clots.Histopathological examination displayed that intestinal villi were broken,thick,short and were shedding,liver swell,hepatic lobule was not clear.Vacuolar degeneration of lymphocytes and infiltration of eosinophils in lymph nodes were observed in spleen.At the same time,the poor environment,poor ventilation and high humidity of pigpens in the pig farm were the main factors leading to the high morbidity of piglet diarrhea.The unstable levels of immune antibodies of pseudorabies,swine fever and porcine reproductive and respiratory syndrome in pig farms are also one of the causes of high morbidity ofthe disease.(2)RT-PCR detection and sequence analysis of the main pathogens of viral diarrhea of pigletsAmong the 111 samples of 7 large-scale pig farms,the positive rate of PEDV was 67.5%(75/111),and the positive rate of Po RV was 10.8%(19/111),and no TGEV was detected.Homology analysis and phylogenetic relationship showed that PEDV ORF 3 gene sequence of 7 representative strains and 3vaccine strains JX188454.1 AJ1102? GU372744.1 Cv777 and JX002703.1 ZJ08 are highly homologous with 94%-99% homology,of which the viral strains is evolutionarily closer to vaccine strain JX188454.1AJ1102,and is relatively far from the vaccine strain GU372744.1 Cv777 and JX002703.1 ZJ08.The homology between PEDV S gene sequences of 7 representative strains and PEDV reference strains was94-99%,The genetic distance between the 7 PEDVs(S)and the vaccine strain JN599150.1 CV777(S)is relatively far,which indicated a distant genetic relationship.However,the situation was opposite in the aspect of the genetic distance with the epidemic strain KY496315.1CH Hubei 2016 and MG334003.1YnP2.The homology of 7 PoRV VP-6 gene sequences and 2 reference strains was 92-98%,and the homology with reference strain L29186.1 4S(swine source)was about 92%,falling in a big evolutionary branch and suggesting a relatively far relationship.The homology between 7 PoRV VP-6 gene sequences and reference strain JN034041.12010/WH-a(wild swine source)was 96%,falling in a small evolutionary branch and indicating a closer relationship.(3)Isolation,Identification and Biological characteristics of diarrhea-causing Escherichia coli of piglets89 Strains of Escherichia coli were isolated from 111 samples,and their physiological and biochemical characteristics all accord with the biological characteristics of Escherichia coli.The isolated strain formed smooth red single colony on Mac Conkey agar and black colony with green light and metallic luster oneosin-methylene blue medium.The PCR amplification and sequence analysis of 10 representative strains showed that the homology with MG270576.1 was between 95%-99%.Phylogenetic relationship showed that the local epidemic strains belonged to the same large branch with the reference strain of Escherichia coli.The drug sensitivity of isolates from different sources was different,but the drug tolerance rates of amoxicillin,compound sulfamethoxazole,tetracycline,kanamycin and other drugs were all over 50%.The results of the animal infection test of representative strains showed that the number of deaths within 18 h was over 50% after mice intraperitoneal injection,and all mice died within 36 h.To sum up,the piglet diarrhea in some large-scale farms in northern Xinjiang was caused by primary infection of epidemic diarrhea virus and secondary infection of Escherichia coli.accompanied by inducements including environment,temperature,season,immune antibody level of pigs and so on.According to the results of sequence analysis of PEDV epidemic strains,and the types of commercial vaccine strains,priority was given to vaccine strain JX188454.1 AJ1102 which had a close relationship with the epidemic strains.For the diarrhea caused by Escherichia coli,choose antibiotics with low drug resistance,such as cefequinoxime,azithromycin,lofloxacin and other drugs for prevention and treatment;Simultaneously,we should pay more attention to keeping the piglets warm,sterilizing environment during labor of sows,strengthening ventilation and reducing all kinds of stress factors.The results of field follow-ups showed that the comprehensive prevention and control measures including immune prevention and control(screening vaccine based on epidemic strain),drug prevention and control(screening drugs based on drug sensitivity test)and eliminating all kinds of pathogenic factors were established in this study,which basically controlled the large area outbreak of piglets diarrhea in the pig farms of the experimental area and.reduced the economic losses of the pig farms. |
PDF Full Text Request