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1.
B. P. Willing A. G. Van Kessel 《Journal of animal physiology and animal nutrition》2009,93(5):586-595
To study microbial influence on intestinal development pertaining to nutrient digestion, two separate gnotobiotic experiments were performed, each with 16 piglets allocated to four treatment groups: germfree (GF), monoassociation with Escherichia coli, monoassociation with Lactobacillus fermentum or conventionalization with faecal bacteria (CV). Enzyme activity and gene expression of lactase phlorizin hydrolase (LPH) and aminopeptidase N (APN) were measured in isolated enterocytes, harvested on day 14, using specific substrates and quantitative PCR respectively. Enterocytes of CV pigs had reduced APN activity, but had increased gene expression relative to GF, making the specific activity:mRNA (A:G) ratio dramatically lower (p < 0.05). Similarly, LPH A:G ratio was significantly reduced (p < 0.05) in enterocytes of CV pigs as compared with GF. The results of co‐incubation of L. fermentum, E. coli and faecal bacteria with APN indicate a direct relationship between enzyme inactivation and specific A:G ratio in enterocytes. We conclude that enterocyte up‐regulation of APN expression occurs as either a direct response to microbial colonization or as a feedback mechanism in response to reduced enzyme activity through microbial degradation. This mechanism may play a role in ensuring effective competition of the host with the intestinal microbiota for available nutrients. 相似文献
2.
Su‐Cheong YEOM Chung‐Gyu PARK Byeong‐Chun LEE Wang‐Jae LEE 《Animal Science Journal》2010,81(2):158-164
Seoul National University (SNU) miniature pigs represent a closed colony with 24 founder pigs and a well preserved pedigree. Characterization using mRNA sequence analysis was conducted for 6 swine leukocyte antigen (SLA) loci in parental or founder pigs, and 17 defined alleles were detected. Based on these complete coding sequences, 17 sequence specific primers (SSPs) were designed for polymorphic sites. To validate the specificity of each allele SSP, the PCR‐SSP was conducted with defined allele clones as templates. PCR‐SSP was conducted with the hot start polymerase and touch‐down PCR. The parental or found SNU miniature pigs showed overall SLA class I and II heterozygotes. Using the established PCR‐SSP method, we conducted SLA typing for breeding stock including 2 pedigreed pigs and identified the novel SLA class II homozygote haplotye (DRA*0201, DRB1*0403, DQA*0102 and DQB1*0701) and 2 SLA homozygote pig lines: SLA class I Hp‐3.0 and class II Hp‐0.3, and SLA class I Hp‐2.0 and class II Hp‐0.2. We thought that our PCR‐SSP SLA typing method could be applicable for new SLA homozygote line establishment by assignment and scheduled breeding. 相似文献
3.
J E Collins D A Benfield W T Christianson L Harris J C Hennings D P Shaw S M Goyal S McCullough R B Morrison H S Joo 《Journal of veterinary diagnostic investigation》1992,4(2):117-126
A recent epizootic of swine infertility and respiratory syndrome (SIRS) in a Minnesota swine herd was investigated. Examination of a sow, neonatal piglets, and stillborn fetuses obtained during the epizootic from the affected herd revealed interstitial pneumonitis, lymphomononuclear encephalitis, and lymphomononuclear myocarditis in the piglets and focal vasculitis in the brain of the sow. Fetuses did not have microscopic lesions. No cause for the infertility and respiratory syndrome was determined. Therefore, attempts were made to experimentally reproduce the disease. Eleven 3-day-old gnotobiotic piglets exposed intranasally to tissue homogenates of piglets from the epizootic became inappetent and febrile by 2-4 days postexposure and had interstitial pneumonitis and encephalitis similar to that seen in the field outbreak. After 2 blind passages in gnotobiotic piglets, tissue homogenates were cultured on continuous cell line CL2621, and a cytopathic virus (ATCC VR-2332), provisionally named SIRS virus, was isolated. Gnotobiotic piglets exposed intranasally to the SIRS virus developed clinical signs and microscopic lesions that were the same as those in piglets exposed to the tissue homogenates, and the virus was reisolated from their lungs. This is the first isolate of SIRS virus in the United States that fulfills Koch's postulates in producing the respiratory form of the disease in gnotobiotic piglets and the first report of isolation and propagation of the virus on a continuous cell line (CL2621). The virus is designated as American Type Culture Collection VR-2332. 相似文献
4.
The objective of this study was to determine whether a chlamydial strain recovered from growing and finishing swine with conjunctivitis or keratoconjunctivitis could cause the same infections in gnotobiotic pigs. The strain shares biological characteristics with Chlamydia trachomatis. After propagation in Vero cells and preparation of the inoculum (10(7) inclusion-forming units/ml), chlamydial strain H7 was instilled into the ventral conjunctival sac (0.15 ml/sac) of 12 anesthetized 3-day-old gnotobiotic piglets. Four age-matched gnotobiotic piglets were anesthetized and sham infected with uninfected cell culture lysates. None of the principal piglets developed clinical symptoms of conjunctivitis or keratoconjunctivitis. Principal piglets necropsied 7 days postinfection (DPI) had histologic lesions of mild or moderate conjunctivitis; immunohistochemical evaluation revealed chlamydial antigen in conjunctival epithelium. A majority of principal piglets necropsied at 14-28 DPI had histologic lesions of mild conjunctivitis, but chlamydial antigen was not detected by immunohistochemistry. The results indicated that chlamydial strain H7 can cause mild or occasionally moderate conjunctivitis in gnotobiotic pigs, but the conjunctival infection is asymptomatic. 相似文献
5.
Generation of α‐1,3‐Galactosyltransferase‐Deficient Porcine Embryonic Fibroblasts by CRISPR/Cas9‐Mediated Knock‐in of a Small Mutated Sequence and a Targeted Toxin‐Based Selection System 
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下载免费PDF全文 M Sato A Kagoshima I Saitoh E Inada K Miyoshi M Ohtsuka S Nakamura T Sakurai S Watanabe 《Reproduction in domestic animals》2015,50(5):872-880
The CRISPR/Cas9 system has enabled the editing of mammalian genomes; however, its applicability and efficiency in the pig genome has not been studied in depth. The α‐gal epitope synthesized by α‐1,3‐galactosyltransferase gene (GGTA1) is known as a xenoantigen obtained upon pig‐to‐human xenotransplantation. We here employed the CRISPR/Cas9 system‐mediated knock‐in of endogenous GGTA1 via targeted homologous recombination (HR). Linearized donors with ~800‐bp homology flanking the CRISPR/Cas9 target site [exon 4 (containing ATG) of GGTA1] served as a template for gene targeting by HR. Using a targeted toxin strategy to select clones lacking α‐gal epitope expression, we successfully obtained several knock‐in clones within 3 weeks of initial transfection. These results suggest that the use of CRISPR/Cas9‐mediated HR to knock‐in a mutated fragment at defined loci represents an efficient strategy to achieve the rapid modulation of genes of interest in swine cells and is a promising tool for the creation of KO piglets. 相似文献
6.
A longitudinal study was undertaken in a newly established specific pathogen-free (SPF) swine herd to determine the dynamics of rotavirus antigen shedding in a closed swine facility. Pregnant SPF gilts which populated the herd, and their offspring, were monitored weekly for three consecutive lactations. Fecal samples were assayed for the presence of group-specific viral antigen by a solid phase immunoassay (ELISA). Results indicate that in the week prior to farrow, 35% of samples from gilts/sows contained rotavirus antigen. During nursing, 37% of the gilts'/sows' fecal samples also contained virus antigen. Over the course of three farrowings, every gilt/sow in the herd excreted virus antigen. Virus antigen was present in 25% of the samples tested from nursing pigs and in 70% of the samples tested from pigs in the postnursing period; 95% of the litters excreted virus antigen either while nursing or postweaning. Seasonal incidence in virus antigen excretion was noted with proportionally more suckling pigs virus antigen-positive in summer and proportionally more sows/gilts positive during winter. Diarrhea occurred only rarely in the sampled population. Although piglets shed rotavirus subclinically, ELISA positive feces from piglets of each lactation caused severe disease when fed to neonatal gnotobiotic pigs. Electropherotyping of these passaged viruses indicated minor variation in RNA banding patterns over time. 相似文献
7.
Groups of gnotobiotic piglets were orally inoculated at 3 days of age with either Helicobacter heilmannii (Hh) or a newly described porcine-origin gastric Helicobacter pylori (Hp)-like bacterium. Three Hh-infected and 6 porcine Hp-like-infected swine were fed a milk replacement diet containing 5-10% (v/v) sterile corn syrup as a dietary source of fermentable carbohydrate. None of the piglets infected with Hh and supplemented with corn syrup developed gastric mucosal ulcers; 2 developed small erosive lesions in the pars esophagea. In contrast, all 6 dietary carbohydrate-supplemented Hp-like-infected swine developed severe gastroesophageal ulcers; 1 of these ex-sanguinated into the stomach and died before the end of the experiment. Four of these 6 piglets had grossly evident partially digested blood in the intestinal lumens, indicative of bleeding into the gastrointestinal tract from the stomach. These data suggest that a high carbohydrate diet and gastric colonization by porcine Hp-like bacteria facilitate development of clinically significant gastroesophageal ulcers. 相似文献
8.
为了克隆甘肃合作猪白细胞抗原(SLA)DRA和DRB基因,分析SLA-DR基因特性和抗原多态性,首次研究了甘肃合作猪在异种移植等研究领域中的应用前景.应用RT-PCR分别扩增合作猪SLA-DRA和SLA-DRB基因并进行测序,将所获得基因序列登录GenBank(登录号分别为FJ905823和FJ9058258),再用NCBI中的BLAST和ExPASy等相关软件进行生物信息学分析.发现在猪-人异种移植中,近亲繁殖的合作猪种在与人类主要组织相容性复合体遗传基因水平相似性方面有一定优势,也可作为备选猪种对相关基因进行必要的修饰和改造. 相似文献
9.
Krakowka S Ellis J McNeilly F Meehan B Oglesbee M Alldinger S Allan G 《Veterinary pathology》2004,41(5):471-481
Tissue section replicates from lymphoid tissues and livers of gnotobiotic swine were examined by immunohistochemistry for the colocalization of porcine circovirus-2 (PCV-2) nucleocapsid and terminal deoxynucleotidyl transferase (TdT)-mediated incorporation of biotinylated nucleotides (UTP) onto the 3'-exposed hydroxyl groups (nick end labeling) nuclear deoxyribonucleic acid (TUNEL), a marker for apoptosis. Single- and dually stained replicates from uninfected controls, subclinically affected PCV-2-infected gnotobiotic pigs, PCV-2-infected piglets immunosuppressed with cyclosporine (Cys), and PCV-2-infected piglets with post-weaning multisystemic wasting syndrome (PMWS) were evaluated. Thymuses were used as positive controls for apoptosis absent PCV-2, tissue sections from dogs given hyperthermic stress were examined as positive controls for induced TUNEL. Tissues from heat-stressed dogs contained TUNEL-positive cell nuclei in both lymphoid tissues and liver, TUNEL was greatest shortly after the delivery of the hyperthermic insult. In uninfected control and subclinically affected PCV-2-infected gnotobiotic pigs, rare hepatocytes and lymphoid cells were TUNEL positive, the frequency of these was similar to that seen in uninfected controls. In PMWS-affected and Cys-treated PCV-2 piglets, the only consistent strongly positive TUNEL signal was contained within the cytoplasm of virus-positive phagocytic mononuclear cells. In phagocytes, some PCV-2 inclusions were TUNEL positive. Collectively, these data indicate that apoptosis is not the primary mechanism of lymphoid depletion and hepatocyte loss in PMWS. Apoptosis associated with systemic viral diseases may be attributable to pyrexia rather than direct or indirect effects of viruses on target cells. 相似文献
10.
One-day-old gnotobiotic piglets were inoculated intranasally with in vitro passaged porcine circovirus 1 (PCV-1), PCV-2, and porcine parvovirus (PPV) alone or in combination (PCV-1/PCV-2, PCV-1/PPV, and PCV-2/PPV). Piglets were evaluated for 1) the development of porcine postweaning multisystemic wasting syndrome (PMWS), 2) distribution of viral antigens by immunochemistry, and 3) viremia and the presence of viral DNA in nasal and ocular secretions and feces. All single agent-infected piglets and piglets infected with PCV-1/PCV-2 or PCV-1/PPV were clinically asymptomatic. They were transiently viremic and seroconverted to homologous virus(es). At termination of the study on postinfection day (PID) 35, microscopic lesions were restricted to focal inflammatory cell infiltrates in livers and myocardia. One piglet given PCV-1/PPV was PPV viremic for 2 weeks after infection and had lymphangiectasia of the spiral and descending colon associated with granulomatous inflammation. All four PCV-2/PPV-inoculated piglets developed PMWS, characterized by sudden onset of depression and anorexia, icterus, and submucosal edema. One piglet became moribund on PID 27, and the remaining three piglets were euthanatized between PID 27 and PID 30 because of severe disease. Lymph nodes were small and the livers were mottled. Disseminated angiocentric granulomatous inflammation was present in all tissues examined except the brain. Multiple lightly basophilic intracytoplasmic inclusion bodies were identified in macrophages and histiocytes. PCV-2 antigen was widely distributed within macrophages; PPV antigen was sparse. Hepatocellular necrosis and bile retention were prominent. PCV-2 DNA was identified in ocular, fecal, and nasal secretions. Terminal sera contained antibodies to PPV (4/4) and PCV-2 (3/ 4). Production of PMWS in gnotobiotic swine appears to require PCV-2 and additional infectious agents such as PPV for full disease expression in gnotobiotic piglets. 相似文献
11.
Miniature pigs of seven swine leukocyte antigen (SLA) genotypes were examined for birth and weaning weights to determine the influence of major histocompatibility (MHC) and background genes on these traits. Effects of different statistical analyses on the magnitude of these associations also were examined. Data on 154 piglets from 32 litters were analyzed by least squares using a linear model that included effects of SLA, litter, and sex of piglet. In these miniature pigs, SLA genotype had little influence on birth and weaning weight; litter, which includes effects of background genes, had a significant effect on both birth weight (P less than or equal to .0001) and weaning (P less than or equal to .005) weight. When litter effects were not accounted for, SLA haplotype appeared to influence both birth (P less than or equal to .001) and weaning (P less than or equal to .10) weights. Use of simple group means, as opposed to least squares means, for comparisons of genotypes yielded misleading results. Simple means indicated that piglets with the aa genotype were heavier (P less than or equal to .01) at birth than those with the cd genotype; in contrast, least squares means showed that cd piglets were slightly heavier at birth (P less than or equal to .10). Heterosis was not observed for birth or weaning weights among piglets of various genotypes, nor did one vs two copies of any haplotype influence these traits. 相似文献
12.
13.
Summary In two groups of swine herds, herds with and without clinical AR the presence of Atrophic Rhinitis (AR) correlated with the presence of toxinogenic Pasteurella multocida (PM) and not with the Bordetella bronchiseptica (BB) infection. Six BB‐ and eighteen PM‐strains have been investigated for AR pathogenicity. Broth cultures were injected intradermally in guinea‐pigs (GPST) orintranasally in 3‐week‐old colostrum deprived specific pathogen free (SPF) piglets. The average atrophy of the ventral conchae (A VC) correlated with the GPST in 4BB‐ and 7 PM‐strains. One BB‐ and 2 PM‐strains were qualified as doubtful, the others as non‐AR pathogenic. With AR pathogenic BB‐ and PM‐strains clinical AR could be induced in 3‐ and 6‐week‐old piglets. AVC lesions (gradation> 1) could be induced with BB in piglets of 6 and with pathogenic PM in 16‐week‐old piglets. Six of seven AR pathogenic PM‐strains resembled Carter‐type D and one resembled type A. No significance was found between AR pathogenicity and somatic serotypes. Intranasal instillations of cell‐free broth culture filtrates of AR pathogenic PM‐strains also caused AR in piglets. These filtrates also caused lethality in piglets and in mice lethalitytest (MLT) and induced a positive GPST. After heating the pathogenic effects of the filtrates disappeared. The name AR toxin has been introduced for this thermolabile, haemorrhagic dermonecrotic (HDNT) fraction of the AR inducing filtrates. The severity of the AR lesions depended on the amount of the AR toxin intranasally instilled in pigs. Cross protecting antibodies obtained in rabbits against the AR toxins of two PM strains could be demonstrated by a toxin neutralisation test in the MLT and the GPST. Broth cultures were injected intradermally in guinea‐pigs (GPST) or intranasally in 3‐week‐old colostrum deprived specific pathogen free (SPF) piglets. 相似文献
14.
近交系五指山小型猪消化器官的解剖学研究 总被引：1，自引：0，他引：1
本研究采用大体解剖学的方法观察了近交系五指山小型猪消化器官的解剖学特征，并对其消化器官的解剖学常数进行测量。结果显示：4月龄较2月龄五指山小型猪近交系部分消化器官的解剖学数据与人的更相似，小肠、大肠和胰腺的形态与人存在较大差异。表明4月龄五指山小型猪近交系部分消化器官比2月龄更适合用于异种移植，但其中一些器官在形态学上不适合整个器官的移植，可能适用于细胞的移植。本试验为比较医学和异种器官移植的研究提供基础资料。 相似文献
15.
Herich R Levkut M Bomba A Gancarcíková S Nemcová R 《Berliner und Münchener tier?rztliche Wochenschrift》2004,117(1-2):46-51
The effects of age, weaning and breeding conditions on the small intestinal morphology and the distribution of immunocompetent cells were investigated. The villus height and numbers of CD3+ T-lymphocytes, measured in the duodenum, jejunum and ileum, were determined in both the gnotobiotic and conventionally bred piglets. The diet of gnotobiotic piglets was composed of milk-replacement and feed mixtures. The application of milk replacement was finished on day 28. Conventional piglets were fed on sow's milk and feed mixtures. The animals were weaned on day 28. Small intestines were collected from 12 conventional and 12 gnotobiotic piglets slaughtered at the age of 2, 7, 14, 21, 28 and 35 days. The morphology results demonstrated that duodenal and ileal villi were significantly higher (p < 0.001) in gnotobiotic piglets during the entire period of the experiment. However, the weight of conventional piglets was higher during the experiment, in some cases significantly (p < 0.05). A marked reduction, in some cases significant (p < 0.001, p < 0.01 respectively), of the villi height on day 7 after the diet change for both groups of animals was recorded. The results demonstrate the differences in the gut development between both groups and their relationship to the breeding conditions. Nevertheless, the effect of crucial diet changes was observed independently of them. The immunohistochemistry results showed significantly (p < 0.001, p < 0.01 respectively) higher numbers of CD3+ T-lymphocytes in the jejunal villi of conventionally bred piglets. Similar results, in some cases significant (p < 0.001, p < 0.01 respectively), were also obtained from the other parts of the small intestine. These observations confirm reduced microorganism exposure under the gnotobiotic conditions. 相似文献
16.
Mycoplasm suipneumoniae and Mycoplasma flocculare in comparative pathogenicity studies 总被引：1，自引：0，他引：1
N F Friis 《Acta veterinaria Scandinavica》1974,15(4):507-518
Three field strains of Mycoplasma suipneumoniae each inoculated into 3 gnotobiotic piglets produced macro- and microscopic lung lesions typical of enzootic pneumonia in 8 of the animals. Under similar conditions 3 strains of M. flocculare produced typical macroscopic lung lesions in just 1 out of 9 animals. It is therefore concluded that M. flocculare is not of primary etiologic importance in the porcine enzootic pneumonia complex.The frequency of successful reisolation from nasal cavities, lungs, and other tissues indicated that the lungs are the sole natural habitat for M. suipneumoniae, while for M. flocculare lungs as well as nasal cavities should be regarded as the natural habitat.None of the organisms apparently spread via the blood stream. M. flocculare, but not M. suipneumoniae, induced histologic alterations of the nasal mucosa. 相似文献
17.
Activation of the immune system is the pivotal event in the production of wasting disease in pigs infected with porcine circovirus-2 (PCV-2) 总被引：39，自引：0，他引：39
Porcine circovirus (PCV)-2, a newly described single-stranded circular DNA virus pathogen of swine is the cause of postweaning multisystemic wasting syndrome (PMWS). In gnotobiotic piglets, PCV-2 infection alone produces asymptomatic infection without evidence of overt PMWS. Gnotobiotic piglets infected with PCV-2 were injected with keyhole limpet hemocyanin in incomplete Freund's adjuvant (KLH/ICFA), and the effects on virus production and development of PMWS were determined. In the first experiment, piglets were injected subcutaneously on the left hip and shoulder, and viral burden was assessed in regional lymph nodes draining the injection sites and in contralateral lymph nodes 13-14 days after infection. Immune activation increased the number of virus antigen-positive cells in draining lymph nodes and increased the amount of infectious virus recovered by 1-4 log10. In a second experiment, the effects of injections of KLH/ICFA with or without concurrent stimulation of peritoneal macrophages by intraperitoneal injections of thioglycollate broth on induction of PMWS was assessed. All immunized piglets developed moderate to severe PMWS, whereas none of the piglets infected with PCV-2 alone developed PMWS. In PMWS-affected piglets, extensive replication of PCV-2 was documented by both immunocytochemistry and quantitative viral titrations. Thus, immune activation is a key component of the pathogenesis of PCV-2-associated PMWS in swine. 相似文献
18.
Interaction with pig ileal explants of Escherichia coli O45 isolates from swine with postweaning diarrhea. 总被引：1，自引：0，他引：1 下载免费PDF全文
下载免费PDF全文 We have previously observed that Escherichia coli O45 isolates from swine postweaning diarrhea (PWD) induced attaching-effacing (A/E) lesions in experimentally inoculated gnotobiotic piglets. In the present work, ileal explant culture has been used as an in vitro model for the study of the development of A/E lesions due to these isolates. The characteristic intimate bacterial attachment and microvilli effacement with cupping and pedestal formation, identical to that observed in gnotobiotic piglets, was demonstrated in pig ileal explants inoculated with O45 E. coli isolates. The initial attachment of bacteria to the enterocytes was observed from 2 to 4 h postinoculation (PI) and full development of A/E lesions was observed within 8 h PI. In this model, we observed that 22 of 25 eaeA-positive O45 isolates induced A/E lesions. However, A/E lesions were not observed for any of 7 eaeA-negative O45 isolates. Thus, we describe a useful in vitro model for the study of A/E capacity of porcine E. coli. Use of this model has enabled us to demonstrate the relatedness of the eaeA gene to A/E capability among porcine O45 E. coli from PWD. 相似文献
19.
Krakowka S Ellis J McNeilly F Waldner C Rings DM Allan G 《The Canadian veterinary journal. La revue veterinaire canadienne》2007,48(7):716-724
Groups (5 to 15 per group) of gnotobiotic swine were infected oronasally with porcine circovirus type 2 (PCV2) at 3 days of age and then given 1 of 6 different commercial Mycoplasma hyopneumoniae (M. hyopneumoniae) bacterins as either a single dose (7 d of age, 1 application products) or 2 doses (7 and 21 d of age, 2 application product). Control groups received PCV2 alone (n = 9) or were infected with PCV2 and immunized twice with keyhole limpet hemocyanin (KLH) emulsified in incomplete Freund's adjuvant (ICFA) (n = 7). Five of 7 (71%) PCV2-infected piglets immunized with KLH/ICFA developed mild or overt PMWS, whereas none of 9 piglets infected with PCV2 alone developed PMWS. Five of 12 (42%) piglets vaccinated with a commercial bacterin containing mineral oil adjuvant developed PMWS following vaccination. None of the PCV2-infected piglets in the other bacterin-vaccinated groups developed PMWS in this model of PCV2-associated disease. This difference in prevalence of PMWS in piglets given the mineral oil-adjuvanted M. hyopneumoniae bacterin and the other M. hyopneumoniae bacterin vaccination groups was statistically significant (P < 0.05). 相似文献
20.
INEXPENSIVE TECHNIQUES FOR THE PRODUCTION AND MAINTENANCE OF GNOTOBIOTIC PIGLETS, CALVES AND LAMBS 总被引：6，自引：0，他引：6
An inexpensive system was developed for the routine derivation and maintenance of gnotobiotic piglets, calves and lambs. Isolator chambers to house these animals were welded in the laboratory from flexible, clear polyvinylchloride film. The isolators consisted of either a simple, closed cylindrical chamber, or for the larger animals, a fibreglass-reinforced plastic (FRP) tub surmounted by a flexible film canopy. The isolators were adaptable for a variety of purposes and most components were interchangeable between isolators. The assembled isolators were sterilised with peracetic acid. Over 300 gnotobiotic piglets, 29 gnotobiotic calves and 18 gnotobiotic or specific pathogen free lambs have been reared successfully by these techniques. Six colostrum deprived foals and a litter of conventional puppies have been successfully maintained in microbial isolation in these isolators. The FRP tub base isolators also proved suitable for housing gnotobiotic weaner piglets. No viral or bacterial cross contamination was detected between isolators housing experimentally infected animals. 相似文献