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1.
M Brugh 《Avian diseases》1988,32(4):695-703
A combination of in vitro and in vivo selection procedures was used to examine the possibility that certain mildly pathogenic field isolates of avian influenza (AI) virus may contain minority subpopulations of highly pathogenic virus. Two mildly pathogenic H5N2 isolates, A/chicken/New Jersey/12508/86 (NJ12508) and A/chicken/Florida/27716/86 (FL27716), recovered from chickens epidemiologically associated with urban live-bird markets, were cloned in trypsin-free chicken embryo fibroblast cultures. Selected clones were inoculated intranasally and intratracheally (IN/IT) into specific-pathogen-free laying hens, and virus reisolated from the hens that died was serially passed in hens by IN/IT inoculation. Several highly pathogenic reisolates were recovered from hens infected with the cloned NJ12508 or FL27716 virus. A highly pathogenic NJ12508 reisolate killed 19 of 24 IN/IT-inoculated hens, and a FL27716 reisolate killed all 24 inoculated hens; signs and lesions were typical of fowl plague. In contrast, uncloned NJ12508 stock virus killed 1 of 24 hens and FL27716 stock virus killed 4 of 24 hens, and neither produced the complete spectrum of lesions associated with fowl plague. Recovery of highly pathogenic viruses from these isolates demonstrates the coexistence of pathogenically distinct subpopulations of virus. Competition for dominance among such subpopulations could explain the variable pathogenicity of some AI viruses.  相似文献   

2.
为了解中国目前H9N2亚型禽流感病毒(avian influenza virus,AIV)血凝素(HA)基因的遗传变异情况,对中国不同地区分离的10株H9N2亚型AIV的HA基因进行扩增、克隆和测序,并对所获得的HA全序列进行同源性和遗传进化分析。结果表明,10个分离株的裂解位点均为RSSR↓GLF,符合低致病性AIV的分子特征;10个分离株有7~9个潜在糖基化位点,由于基因突变有些HA基因出现了新的糖基化位点;与参考株相比,发现了4个抗原表位的突变,这些表位的突变可能引起病毒致病性的改变;受体结合位点除198位有变异外,其他位点均较保守;6株病毒234位氨基酸均为L,具有与哺乳动物唾液酸α,2-6受体结合的特征;10个分离株HA基因与国内疫苗株的核苷酸及氨基酸序列同源性分别为90.4%~99.2%和92.2%~98.7%;10个分离株同属于欧亚谱系中的A/duck/Hong Kong/Y280/97群,但差异显著,为此本试验又将其分为4个不同的亚群。人工感染排毒试验结果表明,BJ15和NJ17分离株在鸡体内具有较强的复制能力,排毒周期较长且排毒量也较大,而S145N的漂变导致在145-147位氨基酸多出1个糖基化位点NGT,可能是分离株复制能力增强的原因。  相似文献   

3.
We characterized Influenza A/H5N1 virus that caused the first outbreak of highly pathogenic avian influenza (HPAI) in chickens in Bhutan in 2010. The virus was highly virulent to chicken, killing them within two days of the experimental inoculation with an intravenous pathogenicity index (IVPI) of 2.88. For genetic and phylogenetic analyses, complete genome sequencing of 4 viral isolates was carried out. The isolates revealed multiple basic amino acids at their hemagglutinin (HA) cleavage site, similar to other "Qinghai-like" H5N1 isolates. The receptor-binding site of HA molecule contained avian-like amino acids ((222)Q and (224)G). The isolates also contained amino acid residue K at position 627 of the PB2 protein, and other markers in NS 1 and PB1 proteins, highlighting the risk to mammals. However, the isolates were sensitive to influenza drugs presently available in the market. The sequence analysis indicated that the Bhutan viruses shared 99.1-100% nucleotide homology in all the eight genes among themselves and 2010 chicken isolate from Bangladesh (A/chicken/Bangladesh/1151-11/2010) indicating common progenitor virus. The phylogenetic analysis indicated that the Bhutan isolates belonged to sub-clade 2.2.3 (EMA 3) and shared common progenitor virus with the 2010 Bangladesh virus. Based on the evidence of phylogeny and molecular markers, it could be concluded that the outbreaks in Bhutan and Bangladesh in 2010 were due to independent introductions of the virus probably through migratory birds.  相似文献   

4.
Lee CW  Song CS  Lee YJ  Mo IP  Garcia M  Suarez DL  Kim SJ 《Avian diseases》2000,44(3):527-535
Sequence analysis of the hemagglutinin (HA) gene of five Korean H9N2 avian influenza virus (AIV) isolates showed that these viruses were closely related and possibly came from the same source. Phylogenetic analysis of the HA1 subunit of H9 subtype isolates revealed that Korean AIV isolates were different from isolates from the poultry markets in Hong Kong in 1997. None of the Korean AIVs had multiple basic amino acids at the HA cleavage site that confer high pathogenicity to some H5 and H7 AIVs. Phylogenetic analysis of the nucleoprotein and matrix gene demonstrated that Korean isolates cluster with Eurasian origin AIVs. The pathogenic potential of one of the isolates (MS96) was assessed after several passages in 14-day-old embryonated chicken eggs (ECE). Fourteen-day-old ECE derivatives of MS96 showed increased HA titer and embryo mortality in eggs; this was apparent after the third passage in 14-day-old ECE. Sequence analysis of the cleavage site of MS96 after the third and tenth passages in 14-day-old ECE revealed no changes in the amino acid sequence. The pathogenicity of MS96 after the tenth passage in 14-day-old eggs (MS96p10(ECE14)) was tested with 4-wk-old specific-pathogen-free chickens. The 14-day-old derivative, MS96p10(ECE14), showed wider tissue tropism and induced more severe clinical signs than the parent virus. Furthermore, after intranasal inoculation of 86-wk-old broiler breeders and 30-wk-old layers, the MS96p10(ECE14) derivative induced more severe signs of depression than the parent virus as well as a transient drop in egg production.  相似文献   

5.
旨在了解浙江地区家禽H3N2亚型禽流感病毒（AIV）的流行变异情况,采用RT-PCR技术对2021年浙江923份样品进行检测,对AIV分离株进行分子特征及遗传演化分析。结果表明,AIV样品阳性率为7.69%（71/923）;共分离到2株鸡源和1株鸭源H3N2亚型AIVs,其HA和NA基因相似性分别为93.4%～100%和94.0%～99.9%,分离株内部基因片段来源复杂,与H1N2、H1N4、H10N7等亚型亲缘关系密切;遗传进化分析显示,H3N2亚型AIV主要流行于华东地区,鸭是其主要宿主,3株H3N2亚型分离株 HA和NA基因均属于禽源进化分支;分离株HA蛋白裂解位点均为PEKQTR↓GLF,符合低致病性禽流感病毒特征,HA蛋白与受体结合相关位点为226Q和228G,PB2蛋白与哺乳动物适应性相关的氨基酸位点为627E,均不同于人流感病毒对应蛋白的相关位点（226L、228S和627K）,推测其跨种传播至人的潜力较低;分离株PB1蛋白的66位氨基酸突变为S,提示其对哺乳动物的致病性可能增强。综上所述,本研究分离的H3N2亚型AIV符合低致病性禽流感病毒特征,基因片段来源复杂,跨种传播至人的潜力较低,但是否影响对宿主的致病性仍需进一步探究。  相似文献   

6.
Ninety-five avian pathogenic Escherichia coli (APEC) isolates recovered from diagnosed cases of avian colibacillosis from North Georgia between 1996 and 2000 were serotyped and examined for typical virulence-factors, susceptibility to antimicrobials of human and veterinary significance, and genetic relatedness. Twenty different serotypes were identified, with O78 being the most common (12%). The majority of the avian E. coli isolates (60%), however, were non-typeable with standard O antisera. Eighty-four percent of isolates were PCR positive for the temperature-sensitive hemagglutinin (tsh) gene and 86% positive for the increased serum survival (iss) gene. Multiple antimicrobial-resistant phenotypes (> or =3 antimicrobials) were observed in 92% of E. coli isolates, with the majority of isolates displaying resistance to sulfamethoxazole (93%), tetracycline (87%), streptomycin (86%), gentamicin (69%), and nalidixic acid (59%). Fifty-six E. coli isolates displaying resistance to nalidixic acid were co-resistant to difloxacin (57%), enrofloxacin (16%), gatifloxacin (2%), and levofloxacin (2%). DNA sequencing revealed point mutations in gyrA (Ser83-Leu, Asp87-Tyr, Asp87-Gly, Asp87-Ala), gyrB (Glu466-Asp, Asp426-Thr), and parC (Ser80-Ile, Ser80-Arg). No mutations were observed in parE. Twelve of the quinolone-resistant E. coli isolates were tolerant to cyclohexane, a marker for upregulation of the acrAB multi-drug resistance efflux pump. Quinolone-resistant isolates were further genetically characterized via ribotyping. Twenty-two distinct ribogroups were identified, with 61% of isolates clustering into four major ribogroups, indicating that quinolone resistance has emerged among multiple avian pathogenic E. coli serogroups and chromosomal backgrounds.  相似文献   

7.
In early 2007, H2N3 influenza virus was isolated from a duck and a chicken in two separate poultry flocks in Ohio. Since the same subtype influenza virus with hemagglutinin (H) and neuraminidase (N) genes of avian lineage was also identified in a swine herd in Missouri in 2006, the objective of this study was to characterize and compare the genetic, antigenic, and biologic properties of the avian and swine isolates. Avian isolates were low pathogenic by in vivo chicken pathogenicity testing. Sequencing and phylogenetic analyses revealed that all genes of the avian isolates were comprised of avian lineages, whereas the swine isolates contained contemporary swine internal gene segments, demonstrating that the avian H2N3 viruses were not directly derived from the swine virus. Sequence comparisons for the H and N genes demonstrated that the avian isolates were similar but not identical to the swine isolates. Accordingly, the avian and swine isolates were also antigenically related as determined by hemagglutination-inhibition (HI) and virus neutralization assays, suggesting that both avian and swine isolates originated from the same group of H2N3 avian influenza viruses. Although serological surveys using the HI assay on poultry flocks and swine herds in Ohio did not reveal further spread of H2 virus from the index flocks, surveillance is important to ensure the virus is not reintroduced to domestic swine or poultry. Contemporary H2N3 avian influenza viruses appear to be easily adaptable to unnatural hosts such as poultry and swine, raising concern regarding the potential for interspecies transmission of avian viruses to humans.  相似文献   

8.
Extraintestinal pathogenic Escherichia coli (ExPEC) isolates were detected in 315/3127 (10.1%) diseased pigs from 19 provinces of China; the frequency of isolation increased from 3.1% in 2004 to 14.6% in 2007. All isolates were characterised for O serogroups, haemolysis, phenotypic and genotypic antimicrobial resistance, virulence genes and pathogenicity. The most prevalent serogroups were O161, O8, O11, O138, O101 and O26; 83/315 (26.3%) isolates were haemolytic. Forty percent of isolates in phylogenetic groups B2 and D were highly virulent porcine ExPEC strains. Thirty-three putative extraintestinal virulence factor genes that are normally associated with human and/or avian ExPEC strains were widely present in porcine isolates. These results indicate that ExPEC are prevalent in pigs in China and represent a potential public health threat.  相似文献   

9.
In this study, we tested the capability of enterobacterial repetitive intergenic consensus (ERIC) and repetitive extragenic palindromic (REP) polymerase chain reaction (PCR) to detect genetic diversity among Escherichia coli strains isolated from chickens bearing clinical signs of colibacillosis and compared the genotypes so obtained with the O:H serotypes and virulence of those strains. The DNAs from 50 avian E. coli strains and from E. coli ATCC 25922 were used to amplify ERIC and REP sequences. DNA from avian strains produced from 8 to 17 bands by ERIC-PCR and from 6 to 20 bands by REP-PCR; E. coli ATCC produced 11 bands by both methods. ERIC and REP-PCR showed good discriminating power, and the dendograms based on the different patterns revealed extensive genetic diversity among the avian strains. Those strains were allocated into four major clonal clusters, each one with 60% of similarity by ERIC and REP-PCR, and those clusters corresponded to strains with different degrees of pathogenicity. However, 56% of the pathogenic strains (28/50) belonged to two out of three major clonal clusters, and 86% of the nonpathogenic strains tended to group in one cluster and one subgroup. The 32 serotypes detected were distributed in all clusters, and within a serogroup, different DNA fingerprints were observed; however, strains with same serotypes tended to form clusters with similarity coefficients greater than 80%. These results suggest that no specific serotype and genotype is responsible for colibacillosis and that REP and ERIC-PCR are reproducible techniques that can improve the studies needed to clarify the pathways to the pathogenesis of colibacillosis.  相似文献   

10.
The natural reservoir of all known subtypes of influenza A viruses are aquatic birds, mainly of the orders Anseriformes and Charadriiformes in which the infection is asymptomatic and the viruses stay at an evolutionary equilibrium. However, mammals may occasionally contract influenza A virus infections from this pool. This article summarizes: (i) natural infections in mammals including pigs, horses, marine mammals, ferrets, minks; (ii) results from experimental infections in several animal models including mice, ferrets, primates, rats, minks, hamsters and (iii) evidence for the increased pathogenicity of the current influenza A H5N1/Asia viruses for mammals. Several reports have shown that a number of mammalian species, including pigs, cats, ferrets, minks, whales, seals and finally also man are susceptible to natural infection with influenza A viruses of purely avian genetic make up. Among the mammalian species naturally susceptible to avian influenza virus the pig and the cat might exert the greatest potential public health impact. Despite numerous studies in animal and cell culture models, the basis of the extended host spectrum and the unusual pathogenicity of the influenza A H5N1 viruses for mammals is only beginning to be unraveled. Recently, also the transmission of equine influenza A virus to greyhound racing dogs has been documented.  相似文献   

11.
This study identified potential virulence markers in 93 eae-positive and 179 eae-negative Shiga toxin-producing Escherichia coli (STEC), isolated from a random sampling of healthy cattle in southwestern Ontario. PCR amplification was used to identify genes for enterohemorrhagic E. coli (EHEC)-hemolysin, the EAF plasmid, and bundle-forming pili (Bfp); adherence to HEp-2 cells and to bovine colonocytes, and the fluorescent actin staining (FAS) test were used to characterize interaction of the bacteria with epithelial cells. The EHEC-hemolysin sequences were detected in 98% of eae-positive isolates compared with 34% of eae-negative isolates. All isolates were negative for EAF and bfp sequences. There was 100% correlation between localized adherence (LA) to HEp-2 cells and the FAS test. Forty-eight (52%) of the eae-positive isolates were LA/FAS-positive, whereas none of the 179 eae-negative isolates was positive in either test. Among the eae-negative isolates, 20 (11%) showed diffuse adherence and 5 (2.8%) showed enteroaggregative adherence to HEp-2 cells. Seventy-three percent of the eae-positive isolates adhered to bovine colonocytes, whereas only 26% of 120 eae-negative isolates that were tested adhered. All 13 O157:H7 isolates were positive for eae and EHEC-hemolysin gene sequences, LA/FAS, and adherence to bovine colonocytes. It is concluded that possession of genes for eae and EHEC hemolysin is correlated with the serotype of STEC, that production of EHEC hemolysin was highly correlated with serotypes implicated in human disease, and that none of the potential markers that were examined can be used to predict the potential virulence of an isolate.  相似文献   

12.
A total of 38 Newcastle disease virus (NDV) isolates were obtained from 6060 fecal samples from northern pintail (Anas acuta) ducks collected in the Tohoku district in Japan during 2006-09. One isolate from each sampling location and date was selected for a total of 38 isolates, then 15 of these were characterized for their pathogenicity by mean death time of minimum lethal dose (MDT/MLD) using chicken embryos and by plaque formation on chicken embryo fibroblasts. Furthermore, nine isolates were randomly selected from these 15 isolates, and the fusion protein genes were sequenced to characterize amino acid sequences around the cleavage site. All 15 were confirmed to be nonvirulent by MDT/MLD test, and nine isolates were also confirmed as nonvirulent by the cleavage site of the fusion protein 112G/E-K/R-Q-G/E-R*L117 that was specific for nonvirulent NDVs. The characteristics of nine isolates identified by phylogenic analysis of the fusion protein gene indicated that the isolates belong to genotype I or II. In addition, we also isolated 68 avian influenza viruses and 28 other hemagglutinating viruses. Our data indicate that northern pintails are subclinically infected by, perpetuate, and distribute NDV along with different subtypes of avian influenza viruses and other hemagglutinating viruses during their migrations across vast areas over the Northern Hemisphere to Japan.  相似文献   

13.
鸭源禽流感病毒的分离和鉴定   总被引：18，自引：1，他引：18  
从南京鸡鸭加工厂、孝陵卫鸭场及迈皋桥鸭场共采制１１３个泄殖腔拭子,用鸡胚尿囊腔接种传代法分离到４株禽流感病毒（ＡＩＶ）,每个样品均有ＮＤＶ混感。纯化后的分离株利用电镜负染技术观察到典型的ＡＩＶ粒子。琼扩试验证明４个分离株均为Ａ型流感病毒。经血凝素亚型分析,４株均属于Ｈ９亚型。致病性试验结果表明,４株鸭源禽流感病毒对鸡均表现为较低的致病力。本研究提示环境（特别是水体）保毒是ＡＩＶ得以长期存在和传播的重要因素和媒介。  相似文献   

14.
The purpose of this study was to determine the presence of stx genes in avian pathogenic Escherichia coli (APEC). We examined 97 APEC isolates: 34 from lesions of avian cellulitis, 31 from avian septicemia, 13 from swollen head syndrome (SHS) in chickens, and 19 from diseased turkeys. We also examined five isolates from the feces of healthy chickens. All 102 E. coli isolates were tested for the presence of stx genes by PCR amplification and by colony blots using probes specific for stx1 and stx2. Fifty-three percent (52) of the 97 APEC carried stx gene sequences: one isolate carried stx2 sequences, two carried both stx1 and stx2 sequences, and the remaining 49 isolates carried only stx1 sequences. Twenty-six isolates were positive by both hybridization and PCR amplification, 10 were positive by PCR only, and 16 were positive by hybridization only. All the stx-positive isolates were negative by PCR for the eae and E-hlyA genes. The five isolates from healthy chickens were all negative for stx. All 13 SHS isolates were positive for the stx1 gene and had low titres for cytotoxicity in the Vero cell assay (VCA). Other stx-positive isolates were negative in the VCA. The stx1 gene from one SHS E. coli isolate was cloned and sequenced and shown to be identical to that of the stx gene of Shigella dysenteriae. The observations indicate that stx1 gene sequences are widespread among APEC but that cytotoxicity on Vero cells is uncommon.  相似文献   

15.
Evolution of avian influenza viruses   总被引：26，自引：0，他引：26  
Although influenza viruses can infect a wide variety of birds and mammals, the natural host of the virus is wild waterfowl, shorebirds, and gulls. When other species of animals, including chickens, turkeys, swine, horses, and humans, are infected with influenza viruses, they are considered aberrant hosts. The distinction between the normal and aberrant host is important when describing virus evolution in the different host groups. The evolutionary rate of influenza virus in the natural host reservoirs is believed to be slow, while in mammals the rate is much higher. The higher rate of evolution in mammals is thought to be a result of selective pressure on the virus to adapt to an aberrant host species. Chickens and turkey influenza virus isolates have previously and incorrectly been lumped together with wild waterfowl, gull, and shorebird influenza viruses when determining rates of evolutionary change. To determine mutational and evolutionary rates of a virus in any host species, two primary assumptions must be met: first, all isolates included in the analysis must have descended from a single introduction of the virus, and second, the outbreak must continue long enough to determine a trend. For poultry, three recent outbreaks of avian influenza meet these criteria, and the sequences of the hemagglutinin and nonstructural genes were compared. Sequences from all three outbreaks were compared to an avian influenza virus consensus sequence, which at the amino acid level is highly conserved for all the internal viral proteins. The consensus sequence also provides a common point of origin to compare all influenza viruses. The evolutionary rates determined for all three outbreaks were similar to what is observed in mammals, providing strong evidence of adaptation of influenza to the new host species, chickens and turkeys.  相似文献   

16.
为了解H6N6亚型禽流感病毒(AIV)的生物学特性,本研究对2015年在广东活禽交易市场分离的一株鸭源AIV DK/GD/S1182/2015(H6N6)进行了全基因组测序、遗传演化分析和对BALB/c小鼠的感染性试验。序列分析显示,该病毒的HA蛋白裂解位点处仅有一个碱性氨基酸,符合低致病性AIV的分子特征;HA蛋白的222V和228S,可以增强病毒对α-2,6唾液酸受体的结合能力。NA蛋白颈部有11个氨基酸的缺失,这将会影响NA的神经氨酸酶活性;该病毒可能是2010年广东H6N6猪流感病毒与2014年广西AIV重组产生。小鼠感染性试验表明,该分离株不需要预先适应就能够在小鼠的肺脏内高效复制,提示该分离株具有感染哺乳动物的潜在风险。本研究对H6亚型AIV监测和相关生物学特性研究具有一定的指导作用。  相似文献   

17.
Pathogenicity of 17 Campylobacter isolates for pregnant guinea pigs was investigated. Of 14 isolates, 12 (86%) produced rates of abortion ranging from 13% to 87%. Two isolates did not produce abortion. Reference strains of C fetus subsp venerealis produced abortion in 60% to 87% and C fetus subsp fetus produced abortion in 60% of the guinea pigs. Inoculated organisms were recovered from uterus, blood, liver, kidney, spleen, and gallbladder of the guinea pigs at rates as high as 83% for 2 ovine isolates and as low as 13% for 2 bovine and 1 human isolates. Most isolations were from the uterus. Two avian isolates were not recovered. Within the C jejuni and C coli group, the ovine and the human isolates appear to be more pathogenic. Swine, bovine, and avian isolates were less pathogenic. Seemingly, the pregnant guinea pig was a suitable and practical model for evaluating the pathogenicity of Campylobacter organisms, regardless of their host of origin.  相似文献   

18.
Colibacillosis caused by avian pathogenic Escherichia coli (APEC) is a leading cause of economic loss to the poultry industry worldwide. The ability of APEC to cause disease is determined by certain virulence markers, some of which are located on pathogenicity islands (PAls). We recently described one such PAI in an APEC O1:K1 strain (APEC-O1). This PAI, termed PAI I(APEC-O1), carries the genes of the pap operon, a region similar to the tia invasion determinant of enterotoxigenic E coli; ireA, a gene that encodes an iron-responsive element; and a novel 1.5-kb region, ORF 54. Here, the occurrence of six selected loci of PAI I(APEC-O1) (papA, papC, papG, ireA, tia, and ORF 54) among APEC and fecal E. coli strains from apparently healthy chickens (avian commensal E. coli) was determined using polymerase chain reaction (PCR) techniques. None of the commensal E. coli was positive for all six traits, whereas 7.2% of the APEC isolates were positive for all the traits. Although there was no significant difference in the occurrence of ORF 54 among APEC and commensal E. coli, tia, ireA, papC, and papG genes were predominantly present in APEC rather than in avian commensal E. coli. papA was detected in only 6.3% of APEC, perhaps because of the presence of allelic variants of the gene. Additionally, the presence of all six traits was tested with PCR in APEC isolates collected in the 1980s, and these results were compared with those obtained with the APEC isolated in the 1990s. There was no significant difference in the occurrence of tia, ireA, papC, papG, and ORF 54 between APEC isolates collected during the different decades. However, papA was more frequently present in APEC from the 1980s than it was in APEC from the 1990s. Phylogenetic group of an isolate did not correlate with pathogenicity or the presence of PAI traits, except that more APEC of the low-pathogenicity group belonged to the phylogenetic group B1. However, PAI traits occurred more frequently in isolates belonging to the intermediate- and high-pathogenicity groups than in isolates of low pathogenicity.  相似文献   

19.
参照NDV评价毒力的方法对1998—2008年间收集的25株H9N2AIV的致病性进行了比较研究。结果显示,25株H9N2AIV不同毒株间致病性有较大差异,大致分为3类：致病性偏强、致病性中等和致病性较弱。从中选出致病力有差异的8个毒株进行了1日龄雏鸡脑内接种指数（ICPI）、6周龄鸡静脉接种指数（IVPI）以及8周龄SPF鸡人工感染排毒试验,结果证明大部分毒株ICPI和IVPI基本上为0,排毒散毒的高峰期在攻毒后第5天到第6天。在25个毒株中,3#和12#表现出了比较高的致病性,不仅其EID50值最高（分别为10-8.8/0.2mL和10-8.8/0.2mL）、ELD50值最高（分别为10-7.9/0.2mL和10-8.7/0.2mL）,而且鸡胚平均死亡时间也最短（分别为66.5,69h）。3#、12#还出现了1日龄雏鸡脑内接种指数（分别为0.238,0.437）和6周鸡静脉内接种指数（分别为0.34,0.51）。在8周龄SPF鸡人工感染排毒试验中3#和12#毒株的排毒量大,排毒时间也明显长于其他毒株（第2～9天）。以上试验结果表明我国H9N2AIV不同毒株致病性有明显差异,呈多态性,致病性偏强的毒株造成鸡群较高的死亡率。  相似文献   

20.
Groups of turkeys were exposed to different isolates of avian influenza virus from wild mallard ducks and domestic turkeys by the intracerebral, intravenous, intratracheal, and intra-airsac routes, and pathogenicity indices were calculated. For the intracerebral pathogenicity study, body weight was also measured. For intravenous, intratracheal, and intra-airsac pathogenicity studies, necropsy lesions were scored and serological responses were recorded. Only the intracerebral pathogenicity index and body weight gain post intracerebral infection demonstrated any differences between isolates. The other procedures failed to demonstrate any pathogenicity whatsoever. There was a correlation (R = 0.73) between intracerebral pathogenicity index and reduced weight gain postinfection. These studies suggest that growth suppression may be an objective measure of pathogenic potential of influenza viruses found to be nonpathogenic by other methods.  相似文献   

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