Immunogenicity and safety of an attenuated Bordetella bronchiseptica vaccine in pigs

The immunogenicity and safety of an attenuated Bordetella bronchiseptica vaccine for swine atrophic rhinitis (AR) was evaluated in 22 hysterectomy-produced, colostrum-deprived pigs and 18 conventional pigs. None of 8 pigs inoculated at 7 days of age intranasally with greater than or equal to 3 X 10(5) colony-forming units (CFU) of vaccinal strain/pig and 2 of 5 pigs inoculated at 7 days of age intranasally with 3 X 10(4) CFU of the vaccinal strain/pig developed AR after intranasal challenge exposure with a virulent strain at postinoculation week (PIW) 3. The remaining 3 vaccinated pigs and 4 nonvaccinated pigs developed AR. Thirteen pigs were inoculated intranasally with 3 X 10(6) to 3 X 10(9) CFU of the vaccinal strain at 7 days of age. At PIW 12, the pigs were killed and necropsied. None of the pigs had clinical signs of AR and/or pneumonia. Virulence was studied by transmission of vaccinal strain through 3 serial growing passages on the nasal mucosa of a litter of hysterectomy-produced colostrum-deprived pigs. Inoculum (nasal swab samples from 2 pigs 4 days after inoculation with 10(8) CFU of vaccinal strain at 5 days of age) was inoculated into the nasal cavity of 2 nonvaccinated pigs. This procedure was repeated 3 times. After the 1st passage, the vaccinal strain was recovered on postinoculation day 4, but after postinoculation day 4, the vaccinal strain was not recovered until the end of the 3rd passage. Turbinate atrophy or pneumonia was not recognized in these inoculated pigs. The vaccinal strain provided immunogenicity without ill effects.     

Oral transmission of porcine reproductive and respiratory syndrome virus by muscle of experimentally infected pigs

The current study was performed to determine if porcine reproductive and respiratory syndrome virus (PRRSV) could be transmitted to pigs by feeding muscle tissue obtained from recently infected pigs. Muscle obtained from pigs infected with either a European strain (EU donor pigs) or American strain (US donor pigs) of PRRSV was fed to PRRSV-free receiver pigs. The donor pigs were slaughtered 11 days post-infection (dpi). PRRSV was detected by conventional virus isolation in muscle at 11 dpi from 7 of 12 EU donor pigs and 5 of 12 US donor pigs. In contrast to conventional virus isolation, all muscle samples from infected pigs were positive for viral nucleic acid by PCR, except for muscle from one animal infected with the American strain of PRRSV. Five hundred grams of raw semimembranosus muscle from each of the donor pigs was fed over a 2 days period (250 g per day) to each of two receiver pigs (48 receiver pigs). The receiver pigs were housed separately in five groups. One of the five groups was fed muscle obtained from US donor pigs that was also spiked with the American strain of PRRSV. Sentinel pigs were placed in-contact with the group of receiver pigs fed spiked muscle. All receiver pigs became viraemic by 6 days post-feeding (dpf). There was evidence of horizontal transmission with sentinel pigs, in-contact with receiver pigs, becoming viraemic. The study demonstrates that PRRSV could be infectious through the oral route via the feeding of meat obtained from recently infected pigs.     

Efficacy of a pseudorabies virus vaccine based on deletion mutant strain 783 that does not express thymidine kinase and glycoprotein I.

The vaccine efficacy of a genetically engineered deletion mutant strain of pseudorabies virus, strain 783, was compared with that of the conventionally attenuated Bartha strain. Strain 783 has deletions in the genes coding for glycoprotein I and thymidine kinase. In experiment 1, which had a 3-month interval between vaccination and challenge exposure, strain 783 protected pigs significantly (P less than 0.05) better against virulent virus challenge exposure than did the Bartha strain. The growth of pigs vaccinated with strain 783 was not arrested, whereas that of pigs vaccinated with the Bartha strain was arrested for 7 days. Of 8 pigs given strain 783, 4 were fully protected against challenge exposure; none of the pigs given strain Bartha was fully protected. In experiment 2, which had a 3-week interval between vaccination and challenge exposure, the growth of pigs vaccinated with strain 783 was arrested for 3.5 days, whereas that of pigs vaccinated with the Bartha strain was arrested for 6 days. In experiment 3, pigs with moderate titer of maternal antibodies were vaccinated twice IM or once intranasally with either strain 783 or Bartha and were challenge-exposed 3 months after vaccination. Pigs given strain 783 twice IM were significantly (P less than 0.05) better protected than were the other pigs. They had growth arrest of only 6 days, compared with 9 days for pigs of other groups, and shed less virus after challenge exposure. Results of this study indicate that the vaccine based on the deletion mutant strain 783 is more efficacious than is the Bartha strain of pseudorabies virus.     

A comparison of the pathogenicity of two strains of hog cholera virus: 1. Clinical and pathological studies

The virulence of a strain of hog cholera virus isolated during an outbreak of mild disease in pigs in New South Wales in 1960/61 (the NSW strain) was compared over 11 days with that of a virulent strain by inoculating 8 pigs with each virus and comparing the ensuing clinical signs and pathology. Both viruses caused persistent pyrexia and leukopenia, the NSW strain 4 to 5 days and the virulent strain 3 days, after inoculation. Few other clinical signs were observed in the pigs inoculated with the NSW strain. In contrast, all pigs inoculated with the virulent strain became progressively depressed and incoordinated, and were killed between days 6 and 9. Bronchopneumonia and swollen, reddened lymph nodes were observed in pigs inoculated with both viruses. Few other gross lesions were observed with the NSW strain, but some pigs receiving the virulent strain had pustules in the tonsil and the anterior oesophagus, petechial haemorrhages in the kidney, and small infarcts at the margins of the spleen. There were marked differences in the histopathology, both in the variety of organs affected and the severity of lesions in individual organs. Suppurative bronchopneumonia occurred in both groups. Other changes in the pigs affected with the NSW strain were colitis, mild cerebral vasculitis, necrosis, haemorrhage and neutrophil infiltration in some lymph nodes and spleens. In pigs infected with virulent virus the cerebral vasculitis was so severe that there was necrosis of cells within the vessel walls.(ABSTRACT TRUNCATED AT 250 WORDS)     

Conjunctival and intramuscular vaccination of pigs with a live avirulent strain of Salmonella cholerae-suis

An avirulent mutant strain of Salmonella cholerae-suis was cloned for resistance to streptomycin and nalidixic acid. The mutant strain 33-13 also was used because of its avirulence and immunogenicity in mice. Weaned pigs were vaccinated with live strain 33-13; 5 pigs were vaccinated by conjunctivally administered 5.5 X 10(7) organisms (low dose), 5 were conjunctivally administered 5.5 X 10(9) organisms (high dose), and 5 pigs were administered 5.5 X 10(9) organisms (high dose) IM. Transient fever and transient fecal shedding of the vaccine strain developed in pigs vaccinated IM, but not in 2 groups of pigs vaccinated conjunctivally. After intratracheal administration of virulent strain 38-9, nonvaccinated control pigs (n = 9) developed persistent high fever, anorexia, bacteremia, diarrhea, and fecal shedding of strain 38-9, whereas vaccinated pigs remained afebrile and clinically normal. Nonvaccinated and uninfected sentinel pigs (n = 8) were kept in units of 2 pigs with each group of experimental pigs, and remained healthy throughout the experiment. Thirteen vaccinated and 7 nonvaccinated control pigs were killed 42 days after vaccination, and 2 vaccinated, 2 nonvaccinated, and 8 sentinel control pigs were killed 58 days after vaccination. Ten organs were evaluated by quantitative bacteriology on necropsy of all pigs for the presence of vaccine strain 33-13, and for virulent strain 38-9. Strain 33-13 was not found. Lung and liver, lesions were found in most of the nonvaccinated control pigs, with a high frequency of recovery of large numbers of strain 38-9 from the mesenteric lymph nodes, lungs, liver, and ileum.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of dexamethasone on the multiplication of attenuated strains of hog cholera virus in pigs

The spread and multiplication of three attenuated strains of hog cholera (HC) virus was investigated in pigs immunosuppressed with a synthetic corticosteroid (dexamethasone). The distribution and degree of multiplication of the ROVAC lapinized strain of HC virus was enhanced in immunosuppressed pigs in comparison to results in untreated pigs, whilst no differences were noted for the Chinese lapinized strain of HC virus, and only slight variations using the tissue culture attenuated GPE strain.The suggestion is made that the results indicate a higher degree of attenuation in the Chinese and GPE strains of HC virus in comparison with the ROVAC strain.     

Multiplication and immunogenicity of a temperature-sensitive and thymidine kinase-deficient strain of Aujeszky's disease virus in pigs.

Hysterectomy-produced colostrum-deprived 5- and 27-day-old pigs were inoculated intramuscularly (IM) or intranasally (IN) with the temperature-sensitive and thymidine kinase-deficient ZHtsTK- strain of Aujeszky's disease virus (ADV), and the nasal swabs and organs of the pigs were periodically collected for virus isolation. No abnormal clinical signs were observed in these pigs, except for a mild febrile response. Viral shedding in the nasal swabs with low titers was detected in the pigs inoculated IN between postinoculation day (PID) 1 and 5, but not in those of the pigs inoculated IM. No contact infection, however, occurred in the cohabiting pigs. Viruses with low titers were isolated only from the muscles and lymph nodes at the site of inoculation in the pigs inoculated IM on PID 2 and 4, but not from any organs of the pigs inoculated IN. To investigate the ability of the ZHtsTK- strain to establish a latent infection in pigs, the pigs inoculated IM or IN with the ZHtsTK- strain were treated with prednisolone. No virus was detected in the trigeminal ganglia or the nasal swabs collected after prednisolone treatment by the cocultivation method. The immunological evaluation demonstrated that immunization of pigs with this strain was effective in preventing clinical signs caused by ADV infection. The duration of virus shedding was markedly shortened in immunized pigs, particularly in those immunized twice and the total quantity of virus recovered from immunized pigs was reduced in comparison with unimmunized pigs.     

The effect of vaccination with the PAV-250 strain classical swine fever (CSF) virus on the airborne transmission of CSF virus

The airborne transmission of Classical Swine Fever (CSF) virus to susceptible pigs, as well as the effect of vaccination with the CSF virus PAV-250 strain was investigated on this mode of transmission. Experiment I: four pigs were inoculated with the ALD CSFV strain (10(4.3) 50% TCID) by the intramuscular route, and at the onset of fever, they were introduced into an enclosed chamber. At the end of the experiment surviving pigs were sedated, anesthetized and euthanatized. Experiment II: four pigs were previously vaccinated with the CSF virus PAV-250 strain, and at 14 days post-vaccination they were challenged with the CSF virus ALD strain. In both experiments, four susceptible pigs were exposed to infectious aerosols by placing them in a chamber connected by a duct to the adjacent pen containing the infected animals and were kept there for 86 hs. In Experiment I, pigs exposed to contaminated air died as a result of infection with CSF virus on days 14, 21 and 28 post-inhalation. These four pigs seroconverted from day 12 post-inhalation. CSF virus was isolated from these animals, and the fluorescent antibody test on tonsils was positive. In Experiment II, a vaccinated pig exposed to contaminated air did not seroconvert, nor was CSF virus isolated from lymphoid tissues. However, mild fluorescence in tonsil sections from these pigs was observed. In conclusion, CSF virus was shown to be transmitted by air at a distance of 1 m to susceptible pigs. Vaccination with the PAV-250 CSF virus strain protected the pigs from clinical disease under the same conditions.     

Protective immunity to toxoplasmosis in pigs vaccinated with a nonpersistent strain of Toxoplasma gondii

The RH strain of Toxoplasma gondii is highly virulent; 1 infective organism is uniformly lethal for mice. Three pigs inoculated SC with 10(3) tachyzoites of the RH strain developed fever, but otherwise remained normal, and T gondii was not demonstrated in their tissues by bioassay into mice. To determine whether vaccination with the RH strain could induce protective immunity to oral challenge with T gondii oocysts, 12 pigs were divided into 3 groups (A, B, C) of 4 pigs each. Pigs in groups A and B were inoculated IM with 10(6) tachyzoites of the RH strain and 4 pigs in group C served as uninoculated controls. Except for fever, the pigs remained clinically normal after inoculation with the RH strain and T gondii was not found by bioassay in mice of tissues from 4 pigs euthanatized 64 days after inoculation. Pigs in groups B and C were challenge-inoculated orally with 10(4) (4 pigs) or 10(5) (4 pigs) T gondii oocysts 72 days after vaccination with the RH strain. The previously uninoculated pigs developed fever, anorexia, and diarrhea from 3 to 8 days after the oocyst challenge. One of the 2 pigs given 10(5) oocysts became moribund because of toxoplasmosis and was euthanatized 9 days after inoculation. Pigs vaccinated with the RH strain remained free of clinical signs after challenge with oocysts. Results of the bioassays indicated that fewer tissue cysts developed in the RH strain-vaccinated pigs than in the previously uninoculated control pigs.     

Comparative immunohistopathology in pigs infected with highly virulent or less virulent strains of hog cholera virus

Eight pigs were inoculated subcutaneously with a highly virulent hog cholera virus (HCV) strain ALD. The infected pigs developed severe illness and became moribund on postinoculation day (PID) 7 or PID 10. Histologic lesions were characterized by severe generalized vasculitis, necrosis of lymphocytes, and encephalitis. HCV antigen was detected in crypt tonsilar epithelial cells, macrophages, and reticular endothelial cells of lymphoid tissues. Antigen localization corresponded well with histologic lesions. Five pigs were inoculated with less virulent HCV Kanagawa/74 strain and were euthanatized on PID 30. All five infected pigs recovered from the illness but became stunted. They also had a slight follicular depletion of lymphocytes, histiocytic hyperplasia, and hematopoiesis in the spleen. Less virulent HCV antigen was observed in the tonsils, kidneys, pancreas, adrenal glands, and lungs. Although antigen localization was less associated with histologic lesions, immunoreactivity was stronger than that in the pigs infected with the ALD strain of HCV. An almost complete loss of B lymphocytes was recognized in pigs infected with the ALD strain and was correlated with follicular necrosis in lymphoid tissues. Loss of B lymphocytes was not prominent in the pigs infected with Kanagawa/74 strain. The number of CD4+ and CD8+ T lymphocytes was significantly higher than that in the noninfected control pigs.     

Respiratory tract protection upon challenge of pigs vaccinated with attenuated porcine reproductive and respiratory syndrome virus vaccines

In this study, the efficacy of two attenuated porcine reproductive and respiratory syndrome virus (PRRSV) vaccines was assessed. The virological protection in the lungs of vaccinated pigs upon challenge was studied. Also, challenged pigs were exposed to lipopolysaccharide (LPS) to evaluate clinical protection. Six-week-old pigs were immunized intramuscularly with commercial vaccines based on either an attenuated American or an attenuated European virus strain. Non-immunized pigs and pigs intramuscularly inoculated with the virulent Lelystad strain were included as controls. Six weeks after immunization, pigs were challenged either intratracheally or intranasally with the Lelystad strain, and 3 and 6 days later intratracheally exposed to Escherichia coli LPS. After LPS administration, pigs were monitored for clinical signs. At 4 and 7 days after challenge, pigs were euthanized to determine virus quantities in broncho-alveolar lavage (BAL) fluids and in lungs. Challenge virus was recovered from three out of eight pigs that had been primo-inoculated with the Lelystad strain with titers ranging between 0.3 and 3.1 log(10). Fifteen out of sixteen pigs vaccinated with the attenuated American strain were positive for challenge virus and their mean virus titers were similar to those of non-immunized challenge controls. Eleven out of 16 pigs vaccinated with the attenuated European strain were positive for challenge virus and their mean virus titers were 2.0-2.5 log(10) lower than those of non-immunized challenge controls. Thus, the virological protection in the lungs of vaccinated pigs upon challenge was incomplete, but was more pronounced in the homologous situation. Clinical signs upon LPS exposure in both vaccinated groups were not reproducible in two experiments.     

猪伪狂犬病病毒天津变异株R13139对猪的致病性研究

为了解猪伪狂犬病病毒（PRV）变异株R13139株对猪的致病性情况，本试验将PRV R13139株和PRV经典强毒株SC株均以10⁶ TCID₅₀剂量经滴鼻途径接种6和9周龄健康仔猪各3头，空白对照组鼻腔接种生理盐水，通过攻毒后两个年龄段猪的临床症状表现、眼观病例变化、显微病理变化、抗体产生情况及病毒在体内部分情况评定两毒株对猪的致病力差异。结果显示，SC株对6和9周龄猪的致死率分别为66.7%（2/3）和100.0%（3/3），而R13139株对6和9周龄猪的致死率分别为33.3%（1/3）和66.7%（2/3），表明R13139株对猪的致死性弱于SC株，但R13139株引起两个年龄段猪发病时间比SC株早，同时间段的体温升高幅度更高，神经发症状更严重；眼观病理变化发现，R13139株引起的发病猪肝脏坏死现象比SC株更明显，而心脏、肺脏、脾脏、膀胱和脑的病理变化差异不明显；显微病理结果显示，R13139株对病猪的扁桃体、肺脏、肝脏和三叉神经节等组织造成的病理损伤明显强于SC株；PCR结果显示，R13139株在濒死猪扁桃体、脾脏、肺脏、三叉神经节和淋巴节（腹股沟、肠系膜和颌下）等组织脏器中分布比SC株更广泛；应用ELISA检测攻毒猪抗体发现，R13139株诱导PRV-gB抗体产生的时间比SC株早1 d。本研究结果可为揭示中国伪狂犬病重新流行的原因及进一步开展防控技术研究提供科学依据。     

Relationship between virulence and adherence of various enterotoxigenic Escherichia coli strains to isolated intestinal epithelial cells from Chinese Meishan and European large white pigs

In vitro adherence to intestinal epithelial cells by enterotoxigenic Escherichia coli strains bearing K88, K99, F41, or 987P adhesins and of their variants not bearing adhesins (K88-, K99-, or F41-) was investigated in European Large White and Chinese Meishan pigs. Possible relationship between adherence and virulence was also examined. The K88-positive (K88+) strain strongly adhered to intestinal epithelial cells from 26 of 28 Large White pigs. This strain had previously been found to be highly virulent for Large White pigs. The only surviving pig was of nonadherent phenotype, and cells from 4 dehydrated moribund pigs had strong adherence. By contrast, the same K88+ strain found previously to have little pathogenicity for Meishan pigs adhered with variable intensity to cells from 17 of 23 Meishan pigs; correlation was not evident between adherence and virulence. The K99+ F41+ strain of porcine origin and the F41+ strain generally adhered strongly to cells from 24 and 23 Meishan pigs, respectively, and to cells from 25 of 26 Large White pigs. Correlation was not found between adherence and virulence for the 2 strains. A K99+ F41+ strain of bovine origin adhered to cells from 20 of 22 Meishan and 22 of 23 Large White pigs, and a K99- F41+ variant adhered to cells from 19 of 23 Meishan and 23 of 24 Large White pigs. The adhesin-negative variants never adhered to intestinal epithelial cells. Strain 987 known not to readily produce 987P adhesin after in vitro growth never adhered to cells during the test.(ABSTRACT TRUNCATED AT 250 WORDS)     

Hematology and clinical chemistry values of normal and euthymic hairless adult male Dunkin-Hartley guinea pigs (Cavia porcellus)

Hematology and serum chemistry measurements were performed on blood specimens from 12 male Dunkin-Hartley hairless guinea pigs Crl:IAF(HA)BR and 10 haired Dunkin-Hartley male guinea pigs Crl:(HA)BR. Significantly higher activities of alanine aminotransferase, aspartate aminotransferase, amylase, and creatine kinase were observed in the hairless guinea pigs as compared to the haired strain. Alkaline phosphatase activity was found to be lower in the hairless guinea pig. The hairless guinea pigs were found to have serum urea concentrations approximately 46% higher than the normal guinea pig strain. The erythrocytic mean cell volume of the hairless strain was found to be smaller, with a greater hemoglobin content. Hairless guinea pigs were found to have approximately 40% fewer leukocytes with a reversed lymphocyte:neutrophil ratio compared to the haired guinea pigs which had much higher lymphocyte counts.     

猪瘟病毒低毒力毒株FJFQ株的分离鉴定

从福建某猪场分离到 1 株病毒,其在PK 15细胞上的毒价为 106.5 TCID50/mL,该病毒能被猪瘟病毒高免血清所中和(效价为1∶8)。通过 RT -PCR 扩增出猪瘟病毒约250 bp的E2蛋白主要抗原编码区序列,其与几株已发表毒株序列的核苷酸及氨基酸同源性分别为79.9%~87.9%,77.7%~86.6%,与Alfort 株同属于基因二群。经本动物传3代均不表现明显的临床症状。用猪瘟兔化弱毒疫苗免疫后以此分离毒作强攻进行免疫保护相关实验,结果免疫组猪在攻毒前及攻毒后扁桃体 HCFA检测均为阴性,对照组猪扁桃体HCFA于攻毒后1周开始出现阳性结果,且一直持续到试验结束。用分离株免疫本动物后再攻石门毒, 2 头试验猪中 1 头死亡,1头出现临床症状。初步说明,所分离的病毒为猪瘟病毒(命名为CSFV- FJFQ株),可能是一株低毒力毒株,且其免疫原性不好。     

Intestinal lesions caused by a strain of Chlamydia suis in weanling pigs infected at 21 days of age.

The objective of this study was to determine whether a strain of Chlamydia suis shown previously to be an intestinal pathogen in gnotobiotic piglets could cause diarrhea and intestinal lesions in young weanling pigs. Pigs from 2 sows were randomly assigned to 2 groups. Group 1 included 13 pigs that were weaned at 24 hours of age and then housed in isolator units and fed milk replacer and unmedicated starter ration. Group 2 included 8 pigs that nursed their respective sows, consumed unmedicated starter ration, and were weaned at 21 days of age. Ten pigs in group 1 and 6 pigs in group 2 were inoculated orally with 4 x 108 inclusion-forming units of C. suis strain R27 at 21 days of age. Control pigs were inoculated with sham inoculum. The pigs were necropsied 5-14 days postinoculation (DPI). None of the Chlamydia-infected pigs developed diarrhea. Villus atrophy was seen histologically in sections of ileum from Chlamydia-infected pigs in both groups 5 and 7 days DPI. Lymphangitis and multiple lymphohistiocytic and neutrophilic aggregates were seen in the submucosa, tunica muscularis, and serosa of the distal jejunum, ileum, and colon from Chlamydia-infected pigs in both groups 5-14 DPI. Immunostaining of sections of distal jejunum, ileum, and colon from infected pigs revealed chlamydial antigen in intestinal epithelium and in foci of lymphangitis/inflammation. The results indicated that C. suis strain R27 can cause intestinal lesions in young weanling pigs, and the lesions are similar to those seen in gnotobiotic piglets. The results also indicated that strain R27 causes asymptomatic intestinal infections in young weanling pigs, at least under the conditions of this study.     

H9N2亚型禽流感病毒SD18株的传染性及不同途径感染效果比较

【目的】 研究H9N2亚型禽流感病毒(Avian influenza virus,AIV)对哺乳动物的传染性和致病性。【方法】 采集样品进行病毒的分离鉴定,将分离到的病毒以300 μL/只(10⁷ EID₅₀)的剂量通过滴鼻和肺递送方式感染豚鼠,每组各15只,对2组感染效果进行比较,然后通过分离株在豚鼠中的传播能力试验验证其气溶胶传播能力,通过间接免疫荧光试验检测分离株在人支气管上皮细胞上的复制能力。【结果】 试验分离到1株H9N2亚型AIV,命名为SD18,病毒通过肺递送和滴鼻2种攻毒方式感染豚鼠后,肺递送组的排毒量显著高于滴鼻组(P<0.05)。通过对豚鼠肺脏相关模式识别受体和抗病毒蛋白的表达检测发现,2种攻毒方式都能诱导相关的免疫因子Toll样受体3(TLR3)、TLR7、抗黏病毒蛋白(MX)和2',5'-腺苷酸激酶(OAS)表达量极显著上调(P<0.01);2组在攻毒后第6天产生抗体,并呈上升趋势。对SD18 株在豚鼠中的传播能力验证发现,SD18株具有通过直接接触和飞沫传播感染豚鼠的能力,但并未证实气溶胶的产生和传播。对SD18株感染人支气管上皮细胞BEAS-2B后发现,在感染后12 h可检测到病毒,24 h时病毒在细胞内复制能力最强,TLR3、TLR7、MX、OAS、白介素6(IL-6)、IL-8、干扰素-β(IFN-β)相关的免疫因子表达量极显著上调(P<0.01)。【结论】 H9N2亚型AIV SD18株的跨种传播能力变强,具有不经提前适应便可直接感染豚鼠的能力;SD18株具有通过飞沫传播感染豚鼠并使其产生抗体的能力且SD18株可在人支气管上皮细胞BEAS-2B上进行复制。     

Characterization and immunogenicity of an apxIA mutant of Actinobacillus pleuropneumoniae

Actinobacillus pleuropneumoniae is the aetiological agent of porcine pleuropneumonia, a highly contagious and often fatal disease. A candidate live vaccine strain, potentially capable of cross-serovar protection, was constructed by deleting the section of the apxIA gene coding for the C-terminal segment of ApxI toxin of the A. pleuropneumoniae serovar 10 reference strain (D13039) and inserting a chloramphenicol resistance gene cassette. The mutant strain (termed D13039A(-)Chl(r)) produced an approximately 48kDa protein corresponding to the N-terminus of the ApxI toxin, and exhibited no haemolytic activity and lower virulence in mice compared with the parental strain. The mutant was evaluated in a vaccination-challenge trial in which pigs were given two intra-nasal doses of the mutant at 14 days intervals and then challenged 14 days after the last vaccination with either A. pleuropneumoniae serovar 1 (4074) or serovar 2 (S1536) or serovar 10 (D13039) reference strains. The haemolysin neutralisation titres of the pre-challenge sera were significantly higher in the vaccinated pigs than in the unvaccinated pigs. The mortalities, clinical signs and lung lesion scores in the vaccinated pigs were significantly lower than those in the unvaccinated pigs for the serovar 1 challenge. A significantly lower lung lesion score was also observed in the vaccinated pigs, compared with unvaccinated pigs, for serovar 2 challenge. Our work suggests that the mutant strain offers potential as a live attenuated pleuropneumonia vaccine that can provide cross-serovar protection.     

Survival and colonization of orally administered Lactobacillus plantarum 301102 in porcine gastrointestinal tract

The purpose of this study was to evaluate the survival and colonization of Lactobacillus plantarum 301102 in porcine gastrointestinal tract and its influence on the intestinal microflora. This strain was isolated from traditional cheese from Inner Mongolia, China. Fermented milk prepared with strain 301102 was administered to pigs and fecal microflora was examined. Intestinal passage of strain 301102 was monitored by a combination of selection with selective medium and the carbohydrate fermentation test, and confirmed by analysis of plasmid DNA patterns. Colonization of this strain was assessed by recovery 7 days after administration. The numbers of Lactobacillus and Bifidobacterium cells in the feces of pigs administered fermented milk prepared with strain 301102 were increased. This strain was recovered from all the pigs during the administration period, and from four of six pigs 7 days after administration. L. plantarum 301102 can pass through the gastrointestinal tract, balance the intestinal microflora, and colonize the intestinal tract, and is therefore an appropriate candidate for a probiotic.