This study aims to prepare nanobodies for the epitopes of spike protein(S)of porcine ep-idemic diarrhea virus(PEDV),and verify its reactivity.The expression vector pCZN1-SN was con-structed by the prokaryotic expression system,and SN fragment was expressed in prokaryotic ex-pression and purified by Ni-NTA chromatography column.The SN nanobodies were displayed u-sing phage display technology and screened from the natural nanobody library.The results showed that SN fragments with a size of 26 kDa were obtained by prokaryotic induction,and the specific nanobodies were obtained through three rounds screening by phage display technology.One strain with the best reactivity was selected for prokaryotic expression and purified.The nanobodies were obtained with a size of 14 kDa by Western blot and demonstrated to have a good binding ability to PEDV SN protein.In summary,nanobodies with epitope fragments of PEDV S protein were suc-cessfully screened and prepared based on the phage display technology,which provided a new way for the in-depth application of nanobodies.

The purpose of this study is to investigate the effect of TPCK trypsin on the proliferation pattern of porcine epidemic diarrhea virus in Vero cells.The TPCK trypsin and conventional tryp-sin were added for virus proliferation,and RT-qPCR technology was used to analyze the changes in virus adsorption and invasion in Vero cells.The replication ability of porcine epidemic diarrhea vi-rus in Vero cells was explored through growth curve drawing,IFA identification,and cell activity detection.The results showed that the optimal concentrations of TPCK trypsin and conventional trypsin were 1 mg/L and 6 mg/L,respectively.The virus showed a decreasing trend with the pro-longation of TPCK trypsin and conventional trypsin pretreatment time.Adding different pancreatic enzymes during the virus proliferation process did not promote the virus invasion in Vero cells.Af-ter 4 h of invasion,the virus particles of each group gradually increased.By plotting the growth curve,it was found that the virus content of the TPCK trypsin group reached its highest level at 24 h(lgTCID50=(6.30±0.14)/0.1 mL),followed by a decreasing trend at 36 h,and the fluorescence intensity produced at 24 h was higher than that of conventional trypsin.In summary,TPCK trypsin has a better promoting effect on the proliferation of porcine epidemic diarrhea virus in Vero cells.It provided theoretical basis for further research on the mechanism of TPCK trypsin affecting porcine epidemic diarrhea virus proliferation,and also provided data support for the isola-tion and purification of porcine epidemic diarrhea virus epidemic strains.

This study aims to investigate the epidemic variation of porcine circovirus type2(PCV2)and its distribution in swine farms in Henan Province from 2022 to 2023.In this study,1 206 pig blood samples from 18 urban scale swine farms,and 318 pigs and environmental samples from 2 PCV2-positive swine farms in Henan Province were detected by fluorescence quantitative PCR.ORF2 gene sequencing and genetic evolution analysis were performed on the positive samples.The results showed that the positive rate of PCV2 was 7.05％(85/1 206)in Henan Province,11.15％in western Henan Province and 3.03％in southern Henan Province.The positive rate of PCV2 in spring was 11.60％(67/576).A total of 31 ORF2 gene sequences were obtained,of which 23 were PCV2d(74.19％),6 were PCV2a(19.35％),one was PCV2b(3.23％)and one was PCV2c(3.23％).The results of amino acid sequence comparison showed that the mutation sites mainly concentrated on amino acids at positions 40-68 and 180-209.The total positive rate of pig farm sam-ples was 37.42％(119/318),and the positive rate of pig samples from different types of pig houses was 60.71％(34/56),45.83％(11/24),35.09％(20/57),and 33.33(3/9)in order from high to low.The positive rate of environmental samples from high to low was 56.36％(31/55)in feeding system,46.67％(7/15)in feces system,12.50(1/8)in decontamination area,11.11％(2/18)in living area,and no PCV2 was detected in ventilation system.The highest positive rate was 45.00％(9/20)for the tools in the house,7.14％(1/14)for the surface and sole of the clothes after leaving the house,and no PCV2 was detected on the surface and sole of the clothes before entering the house.In this study,the epidemiological investigation of PCV2 in Henan Province and its distribu-tion in swine farms were carried out,and the main circulating strains,seasons,regions and gene mutations of PCV2 in H enan Province were identified.The distribution and transmission routes of PCV2 in positive pig farms were preliminarily analyzed and summarized,which provided data basis and reference for effective prevention and control of PCV and the establishment of accurate bio-safety prevention and control measures.

The SVA and different serotypes of VSV(VSNJV and VSIV)are susceptible to infect pigs and cause blister injuries to the lips and hoof of pigs.The clinical symptoms of diseases caused by these viruses are very similar,which is easy to cause misdiagnosis.Therefore,a multiplex nano-PCR method was developed for the simultaneous defection of VSV,VSNJV and VSIV.In this stud-y,three pairs of specific primers were designed according to the SVA-P gene,VSNJV-N gene and VSIV-N gene.The optimal annealing temperature and optimal primer concentration were tested,and the reaction system and conditions were optimized.We have developed a novel,rapid and sensitive multiple nano-PCR detection method for simultaneous detection of SVA,VSNJV and VSIV,which was developed by using nano-metal materials.The specific test results showed that the method could specifically amplify the target genes of SVA,VSNJV and VSIV,with no cross-reactivity to PRV,ASFV,PCV2 and PHEV.The sensitivity test results showed that the minimum nucleic acid detection of the method was 10 copies/μL,which sensitivity was great.In addition,the optimal primers showed good reactivity and stability to different batches of enzymes and plasmids.There were 7 among 50 of diseased pig samples were SVA positive by multiple nano-PCR detec-tion method,and 5 out of 50 of diseased pig samples were SVA positive by ordinary single PCR method.Moreover,no VSNJV and VSIV were detected by the two methods.In conclusion,this es-tablished multiple nano-PCR detection method has higher specificity and sensitivity in the detec-tion of SVA,VSNJV and VSIV.And this study could provide technical support for the rapid differ-ential diagnosis,prevention and control of swine viral vesicular diseases in clinical settings.

To understand the pathogenicity and drug resistance of swine-derived E.coli and its bio-logical characteristics in some areas in Hebei,E.coli was isolated and identified from diarrheal fe-ces of piglets collected from swine farms,and the isolated strains were subjected to drug sensitivity test,detection of the ability to form biofilm,pathogenicity test,virulence gene test,drug resistance gene test,and identification of phylogenetic subgroups.The results showed that a total of 35 patho-genic E.coli strains were isolated from the feces of diarrheic piglets,and most of the isolates were multidrug-resistant,and were resistant to at least three antibiotics,including amoxicillin(88.57％),ampicillin(88.57％),doxycycline(88.75％),sulfisoxazole(77.17％),lincomycin(100％),and chloramphenicol(100％);the isolates were severely resistant.The isolates all carried virulence genes,with a total of five virulence genes detected,namely,EAST1(77.14％),eaeA(17.14％),stx2e(5.71％),LT(2.86％),and STb(2.86％),and the isolates also carried multi-re-sistance genes,with a total of five virulence genes detected,namely,bla TEM-1(65.71％),bla CTX-M(20.00％),tetA(82.86％),tetB(14.29％),aadA2(17.14％),aac(6')-Ib(14.29％),qnrS(17.14％),sul 1(40.00％),sul2(34.29％),and floR(60.00％);the phylogenetic grouping showed that the isolates had a high proportion of group B1 and group A;and all 35 isolates showed differ-ent pathogenicity after infection of mice.This study provides a reference for the selection of effec-tive therapeutic drugs and the development of prevention and control programs for swine-origin pathogenic E.coli in Hebei Province.

In order to understand the infection status of Escherichia coli(E.coli)in different popu-lations of chickens,E.coli was isolated and identified from 1-day-old chickens,dead embryos,clini-cal dead chickens from 3 hatcheries and 9 broiler farms in Yantai area,and 1 950 samples from e-liminated breeder chickens;the homology of the isolated strains was analyzed by pulsed field gel e-lectrophoresis;virulence genes and serotypes were identified by PCR;pathogenicity was determined by challenge chicken embryos.Drug resistance of the strain was determined by drug sensitivity test.Results showed that a total of 116 strains of E.coli were isolated,of which 97 strains were successfully classified into 66 band types,15 virulence genes and 5 serotype were detected by PCR,and 56,32 and 28 strains were divided into high,medium and low pathogenic strains by chicken embryo challenge test.Results indicated that E.coli from clinically dead chickens and eliminated breeder chickens had higher pathogenicity and drug resistance.This study provides a reference ba-sis for the prevention and control of colibacillosis in chicken farms.

Porcine hemagglutinating encephalomyelitis virus(PHEV)is highly prevalent and wide-ly distributed,and its harm on pig farming is of great concern,therefore,effective strategies for prevention and control are necessary.In this study,chloroquine(CQ)was selected and its effect and mechanism on replication and proliferation of PHEV were investigated.The results showed that CQ(1-100 mmol/L)inhibits the replication and proliferation of PHEV in a dose-dependent manner and has no cytotoxicity on N2a cells.The production of inflammatory cytokines and activa-tion of NF-κB signaling pathway were both inhibited by CQ concentration at 50 mmol/L in PHEV-infected N2a cells.In conclusion,we confirmed the inhibition of CQ in replication and proliferation of PHEV.It is expected to be applied to the prevention and treatment of PHEV in clinical.

To investigate the expression and distribution of follicular dendritic cell(FDC)and follic-ular helper T cells(Tfh)in mouse spleen and lymph nodes induced by foot-and-mouth virus-like particles(FMDV-VLPs),the recombinant pCMV-HA-HBcAg-VP1-VP4 plasmid was transfected into CHO-K1 cells to prepare FMDV-VLPs,and the recombinant FMDV VP1-VP4 protein was expressed and purified through a prokaryotic expression system.BALB/c mice were subcutaneous-ly immunized with FMDV-VLPs(VLP group)and recombinant FMDV VP1-VP4 protein(VP1-VP4 group),and PBS control group(PBS group)was set up.At 21 d post primary immunization(dpi),booster immunization was carried out.Spleen,shoulder lymph nodes,and submandibular lymph nodes were collected at 7,28,42,72 and 102 dpi,and frozen sections were prepared.Immu-nohistochemical staining was used to observe the expression and distribution of FDC and Tfh.The results showed that the number of FDC and Tfh cells in the VLP group in the spleen and lymph nodes showed a gradual increase from 7 to 42 dpi,and gradually decreased to non-immune levels starting from 72 dpi.The results indicate that FMDV-VLPs can induce the formation of GC in the spleen and lymph nodes,and the number of FDC and Tfh cells in GC can last for at least 42 d.This study provides a theoretical basis for the study of the immune memory response mechanism of B cells induced by FMDV virus-like particles.

The receptors of Newcastle disease virus(NDV)are sialic acid receptors that mainly in-clude neu5ac-α-2,3gal-β-1,4Glc(SAα2,3Gal)and neu5ac-2-s-α-2,6Gal10Me(SAα2,6Gal).The distribution and abundance of the two receptors in host cells have important effects on virus sus-ceptibility and intracellular proliferation.In order to further explore the effects of sialic acid recep-tors on susceptibility and proliferation characteristics of NDV different strains,the expression lev-els of SAα2,3Gal and SAα2,6Gal receptors on BHK-21 cell membrane were adjusted by overex-pression and RNAi assays,and the TCID50 values were determined after different BHK-21 cells were inoculated with NDV strains Ⅰ and LaSota.The results suggested that NDV strain LaSota preferentially binds to SAα2,6Gal and strain Ⅰ selectively binds to SAα2,3Gal receptor.Further-more,the viral titers of NDV strains LaSota and Ⅰ in cell culture were positively correlated with the expression levels of SAα2,6Gal and SAα2,3Gal receptors on host cell membrane respectively.In conclusion,our studies provide an understanding of the relationship between infectivity of NDV different strains and receptor types of host cell,and provide a method to increase viral titer of NDV for cell-based vaccine production.

To establish an immunochromatographic method for rapid detection of caprine enterovir-us(CEV),the monoclonal antibody against CEV VP1 protein was used as gold-labeled monoclonal antibodies,and the purified rabbit-derived polyclonal antibody of CEV-VP1 and sheep anti-mouse IgG were used as the detection line and quality control line,respectively.The colloidal gold immu-nochromatographic test strips for CEV were prepared according to the principle of double antibody sandwich,evaluated,and applied for clinical specimen detection.The results showed that the meth-od specifically recognized CEV without cross-reaction with bovine enterovirus and bovine viral di-arrhea virus.The minimum detection limit of the method was 102.49 TCID50/mL and had good re-producibility.The prepared test strips had a shelf life of three months kept at 4 ℃.Detection of clin-ical samples using the immunochromatographic test strips showed 100％coincidence rate with RT-PCR method.In conclusion,the colloidal gold immunochromatographic test strips for detection of the emerging CEV with good specificity,sensitivity and repeatability,which provides a new techni-cal means easily used for the rapid detection/diagnosis and epidemiological investigation on CEV infection.