THE RESPONSE OF AUSTRALIAN CHICKENS NATURALLY INFECTED WITH AVIRULENT NEWCASTLE DISEASE VIRUS TO CHALLENGE WITH VELOGENIC NEWCASTLE DISEASE VIRUS

SUMMARY Sixty-eight breeder chickens, 4 to 12 months of age, were taken from Australian flocks that had been naturally infected with avirulent Newcastle disease virus (NDV) and transported by air to Malaysia. Nearly all the breeders had haemagglutination inhibition antibodies to NDV, at titres of from 2 to 128. Thirty-two were inoculated intranasally with an Asian, velogenic, viscerotropic strain of NDV and all survived this challenge. Thirty-six were exposed to contact infection with the same velogenic NDV and 2 died of Newcastle disease within 14 days. The levels of haemagglutination inhibition antibodies against NDV increased in the surviving breeders after challenge, reaching 2048 or greater in a few birds. Velogenic NDV was isolated from a cloacal swab from one clinically normal breeder 10 days after challenge by contact. Cloacal swabs taken 7 to 10 days after challenge from another 23 breeders yielded no NDV. Twenty-four broilers, 7 weeks of age, were also transported from Australia to Malaysia. All lacked detectable haemagglutination inhibition antibody to NDV and they were from a flock with no detectable antibody to NDV. Twelve were challenged with velogenic NDV intranasally and 12 were subjected to contact challenge. All broilers died of Newcastle disease within 13 days.     

THE SEROLOGICAL RESPONSE OF CHICKENS TO AUSTRALIAN LENTOGENIC STRAINS OF NEWCASTLE DISEASE VIRUS

SUMMARY: Australian lentogenic Newcastle disease viruses were evaluated as uninactivated vaccines in Australian chickens, the response being evaluated by the production of haemagglutination-inhibition (HI) antibodies. Two viruses, V4 and PM9, induced high levels of antibody and were readily transmissible between chickens by contact exposure. Three other viruses were poorly immunogenic and poorly transmissible. Chickens vaccinated intramuscularly with the V4 strain produced higher HI antibody titres than chickens vaccinated by the orotracheal, intranasal and intraocular routes. HI antibody titres in chickens vaccinated with the V4 strain reached peak levels 3 to 5 weeks after vaccination and waned considerably during the next 2 to 4 weeks. However, low levels of HI antibody persisted for at least 36 weeks after vaccination. Intramuscular vaccination with the V4 strain of one-day-old chicks lacking maternal antibody to Newcastle disease virus resulted in 42–70% mortality and the survivors developed very high titres of HI antibody. Similar chickens inoculated orotracheally showed signs of depression and developed high titres of HI antibody, but there were no mortalities. Chickens 1-, 2-, 3- and 4-weeks-old and lacking maternally derived HI antibody to Newcastle disease virus suffered no adverse reaction to intramuscular or orotracheal vaccination. The antibody response of the 1-week-old chickens was considerably poorer than that of the older chickens. Following orotracheal vaccination with the V4 strain, chickens with low levels of maternally derived antibody responded with low levels of HI antibody. On the other hand, in the progeny of hens hyperimmunised with the V4 strain the production of active antibody following orotracheal vaccination was delayed until the level of passive antibody had declined considerably. There was no response to intramuscular vaccination in congenitally hyperimmune chickens. The minimum HI antibody inducing dose of V4 vaccine, when measured 3 weeks after vaccination of 6-weeks-old chickens, was 10^5.6 50% egg infectious doses.     

INTERACTION BETWEEN INFECTIOUS BURSAL DISEASE VIRUS AND NEWCASTLE DISEASE VIRUS IN CHICKENS

The Australian strain of infectious bursal disease virus (IBDV), 002/73, affected the response of chickens to Newcastle disease virus (NDV). The titre of serum antibodies to NDV in chickens infected with IBDV was significantly lower than that of birds infected with NDV alone. It also appeared that IBDV affected NDV excretion from chickens as NDV was more frequently isolated from chickens infected with IBDV, IBDV infection did not alter the pathogenicity of NDV in chickens. This Australian strain of IBDV therefore appeared to be immunodepressive in one-day-old chickens.     

THE ISOLATION OF LENTOGENIC STRAINS OF NEWCASTLE DISEASE VIRUS IN AUSTRALIA

SUMMARY Twelve isolations of Newcastle disease virus were made from 77 clinical samples from chickens with conjunctivitis, respiratory disease, proventriculitis and bursal atrophy. Nine of the Isolations were made from chickens with conjunctivitis. The viruses were identified as Newcastle disease virus by inhibition of their haemagglutinins with specific antiserum to Newcastle disease virus. The viruses failed to kill chicken embryos after inoculation into the allantoic cavity and they were judged to be lentogenic strains. There was no evidence that the Newcastle disease viruses were responsible for any of the clinical conditions from which they were isolated. The presence of other agents in 10 of the samples was indicated by reduced production of haemagglutinin in allantoic fluids of infected embryos, by deaths of infected embryos, by the production of cytopathic changes in avian cell cultures and by electron microscopy. Three isolations of infectious bronchitis virus, 2 of avian adenovirus and one of avian reovirus were made. Other samples were suspected of containing infectious bronchitis virus and mycoplasmas, but these were not isolated. The Newcastle disease viruses failed to produce plaques in chicken embryo fibroblast cell cultures and they were separated from the contaminating agents by haemagglutination and elution followed by passage at terminal dilution in chick embryos. No Newcastle disease virus was isolated from 60 caecal tonsils and 60 lung samples from 9-week-old broiler chickens. Eight lung samples yielded mycoplasmas that caused haemadsorption in chicken cell cultures. The mycoplasmas were probably Mycoplasma gallisepticum.     

AEROSOL VACCINATION OF CHICKENS WITH THE V4 STRAIN OF NEWCASTLE DISEASE VIRUS

SUMMARY Two-week-old chickens, free of detectable maternal antibody to Newcastle disease virus (NDV), or with low levels of maternal antibody, were vaccinated with the V4 strain of NDV. Haemagglutination inhibition (HI) antibodies were determined at intervals after vaccination. Two hundred chickens were vaccinated by exposure to an aerosol, a dose of 10⁶ 50% embryo infectious doses (EID⁵⁰) being allowed per chicken. Forty unvaccinated chickens were placed in direct contact with vaccinated chickens. Most of the vaccinated chickens and the incontact chickens had developed HI antibodies of titre ≥ 8 within 2 weeks of vaccination. The HI antibodies in many chickens persisted for at least 8 weeks. Control chickens in a shed 15 metres from the shed containing the vaccinated chickens did not develop HI antibodies to NDV. NDV could be isolated from some vaccinated chickens for 15 days after vaccination. An aerosol dose of 10⁵EID₅₀ per chicken failed to induce a serological response in 2 groups of 40 chickens each. HI antibodies were produced in 1 of 2 groups, each of 40 chickens, vaccinated with 10⁶EID₅₀ and in both of 2 groups of 40 chickens each vaccinated with 10⁷EID₅₀. Duplicate groups of 40 chickens were vaccinated with 10⁶EID₅₀ of V4 virus per chicken administered either as an aerosol, a coarse spray or a droplet placed in the conjunctival sac. HI antibodies were produced in all the groups of chickens.     

一株鸭源新城疫病毒强毒株的分离与初步鉴定

从表现腹泻、神经症状、肠道粘膜局部出血、坏死以及卵泡充血、出血为特征的病死产蛋鸭分离到一株病毒,经血凝（hemagglutinin,HA）、血凝抑制（hemagglutination inhibition,HI）和血清中和试验（seium neutralization,SN）及部分融合蛋白（F）基因的序列测定初步鉴定为新城疫病毒（Newcastle disease virus,NDV）,命名为JSD0812株。该毒株10日龄SPF鸡胚平均死亡时间（mean deathtime,MDT）为54．6h,1日龄SPF鸡脑内接种致病指数（intracerebral pathogenicity index,ICPI）为1．75,6周龄SPF鸡静脉接种指数（intravenous pathogenicity index,IvPI）为2．68,其F蛋白裂解位点氨基酸序列为^112R—R—Q—K—R—F^117,上述结果符合NDV强毒株的分子特征,证实该毒株为NDV强毒株。致病性试验表明该毒株对鸡、鸭和鹅均有很强的致病性．     

感染鸡贫血病毒雏鸡接种新城疫疫苗后免疫功能和免疫调节的变化

雏鸡1日龄感染鸡贫血病毒，8日龄接种Lasota疫苗，以未感染免疫雏鸡为对照，于免疫后7、14、28d检测血清免疫球蛋白IgG、IgM、IgA,在凝抑制抗体（HI）滴度；胸腺、法氏囊、脾脏T细胞、IgG^ 、IgM^ 、IgA^ ,抗体生成细胞数量及T、B细胞增殖反应；胸腺、脾脏细胞因子IL－2、IFN活性的变化。结果发现，感染CAV雏鸡Lasota疫苗免疫后，其血清IgG、IgM、IgA免疫球蛋白含量明显减少，HI抗体滴度降低；胸腺、法氏囊、脾脏T细胞、抗体生成细胞数量降低及T、B细胞增殖反应减弱，胸腺、脾脏IL－2及TNF诱生活性降低，表明其细胞免疫和体流免疫功能以及细胞因子免疫调节作用均未感染免疫雏鸡明显减弱。     

鹌鹑对新城疫病毒的易感性试验

用从新城疫病死鹌鹑中分离的新城疫病毒(NDV)株(QNDV-1)和鸡新城疫毒株(F_(48)E_8),对5日龄、10日龄、25日龄、35日龄和70日龄等不同日龄鹌鹑进行了感染试验,并用15日龄鹌鹑做了呼吸道、肌肉注射、皮下注射、脑内注射、静脉注射和消化道等不同途径的感染试验。结果表明:供试不同日龄鹌鹑均可被感染发病,并出现和自然病例同样的症状或死亡,随着日龄增长,死亡率有降低趋势,70日龄鹌鹑(成年产卵)出现同自然病例同样的产卵量下降和产出异常卵现象;不同途径均可使鹌鹑感染发病或死亡,其中以脑内注射和静脉注射所表现的发病或死亡最为急剧;从病死鹌鹑中可重新收回到新城疫病毒,发病耐过鹌鹑可产生特异性抗体。     

新城疫病毒弱毒骨架表达强毒F基因的重组病毒生物学特性研究

为了解目前中国新城疫病毒（Newcastle disease virus,NDV）优势基因VIId型的毒力机制,应用反向遗传技术将我国优势流行基因VIId型强毒株I4的F基因替换弱毒LX的F基因,获得表达NDV强毒株I4F基因的重组病毒NDV/LX-If。测定重组病毒的致病指数和组织分布,结果发现,重组病毒NDV/LX-If毒力比骨架病毒有了显著的提高。NDV/LX-If的鸡胚平均致死时间（mean death time,MDT）为56 h,雏鸡脑内接种致病指数（intracebral pathogenicity index,ICPI）为1.49,属于中等毒力,毒力比亲本病毒毒力低,但都能使自然途径感染的鸡100%死亡,同时获得了亲本毒株的组织嗜性。可见,新城疫病毒F基因是毒力和组织嗜性的主要决定因素,但是其它基因对新城疫病毒的毒力也可以产生影响。     

SEROLOGICAL RESPONSE OF CHICKENS, TURKEYS AND DUCKS TO STRAIN V4 OF NEWCASTLE DISEASE VIRUS

SUMMARY The serological response of two different age groups of turkeys and ducks to strain V4 of Newcastle disease virus was markedly inferior to that of similar age groups of chickens. This suggested that this strain might not be a suitable vaccine strain for use in turkeys and ducks, even though the correlation between specific serum antibody and immunity in these species is not clearly understood. The 20-week-old group of chickens required two doses of 10^7–1 50 per cent embryo infective doses (EID₅₀) of the virus to develop a specific serum antibody titre comparable to 21-day-old chickens given one dose of 10^7–1 EID₅₀ of virus.     

感染鸡贫血病毒雏鸡接种新城疫疫苗后局部粘膜免疫功能的变化

雏鸡1日龄感染鸡贫血病毒（CAV），8日龄接种Lasota疫苗，以未感染免疫雏鸡为对照，于免疫后7、14、28d检测其哈德尔腺和盲肠扁桃体T细胞及IgG^ 、IgM^ 、IgA^ 抗体生成细胞数量，泪液、气管液、肠液、胆汁中IgG、IgM、IgA含量以及泪液、胆汁HI抗体滴度的动态变化。揭示了感染CAV雏鸡接种ND疫苗免疫后哈德尔腺、盲肠扁桃体的T细胞和IgG^ 、IgM^ 、IgA^ 抗体生成细胞数量，泪液、气管液、肠液、胆汁中免疫球蛋白IgG、IgM、IgA含量以及泪液、胆汁HI抗体滴度，均较未感染免疫雏鸡明显减少。表明眼部、呼吸道和消化道局部粘膜免疫防御能力减弱。     

ClassI新城疫病毒强毒株融合蛋白的表达时相分析

根据ClassI新城疫病毒分离株9a5b编码序列,设计特异性引物扩增融合蛋白（F）基因截短片段（199～1500nt）,利用原核表达获得重组蛋白,切胶免疫Balb／c小鼠,制备特异性多抗血清,利用制得的血清进行F蛋白表达时相分析。结果表明：NDV9a5b病毒按5M．0．1（multiplicityofinfection,多重感染复数）感染量接种DF1单层细胞,经IFA检测,在感染6h时,F蛋白开始出现,主要分布于细胞浆内;12～16h胞浆申的F蛋白含量逐渐增多,形成包涵体,开始在细胞膜上分布;当病毒感染24h后,F蛋白在细胞膜上形成明显的膜周染色;至感染36h后,出现多个细胞融合的包涵体,细胞已基本崩解。此时,F蛋白也散在分布于包涵体中。这为深入开展F蛋白与该病毒的毒力演化机制研究工作奠定了基础。