THE PATHOGENESIS OF INFECTIOUS AVIAN ENCEPHALOMYELITIS

An association was demonstrated between the development of clinical infectious avian encephalomyelitis (IAE), the persistence and titre of infectious avian encephalomyelitis virus (IAEV) in the brain of the chicken, the duration of detectable viraemia and the age of the chicken at the time of infection with the virus. The older the chicken at the time of infection the milder the disease, the lower the virus titre in the brain and the shorter the period of viraemia. IAEV serum neutralising antibody was produced earlier after infection in older chickens, and its detection was associated with decreasing virus titres in the brain and the cessation of detectable viraemia. Treatment of chickens with testosterone in ova, to inhibit the development of antibody synthesis, prevented the onset of age-associated resistance and testosterone treated birds were as susceptible to clinical IAE as baby chickens. The results suggested that the ability to produce IAEV serum neutralising antibody was an important component of age-associated resistance to IAE.     

THE PATHOGENESIS OF INFECTIOUS AVIAN ENCEPHALOMYELITIS

The age of the chicken at the time of infection with infectious avian encephalomyelitis virus (IAEV) and the route of the administration of the virus had a marked effect on the development of the clinical disease. Chickens given the virus by intramuscular, intraperitoneal and oral routes exhibited a decreased susceptibility to development of clinical disease with increasing age. Irrespective of age, chickens were consistently susceptible to intracerebral inoculation of IAEV. Chickens infected with the virus at 1-, 7- and 14-days of age developed lower neutralising antibody titres to IAEV than chickens infected at 21 and 28 days. A relationship between the ability to produce specific neutralising antibody to IAEV and susceptibility to the development of clinical disease is discussed.     

THE PATHOGENESIS OF INFECTIOUS AVIAN ENCEPHALOMYELITIS

Infectious avian encephalomyelitis virus (IAEV) maternal antibody was detected in the serum of chickens for up to 21 days following hatching. This antibody protected chickens against clinical IAE after intracerebral inoculation with van Roekel strain or oral administration of the NSW-1 strain of IAEV. Maternal antibody to IAEV also protected testosterone bursectomised chickens against the development of clinical disease. IAEV maternal antibody also influeced the pattern of virus excretion in faeces and serological responsiveness. This influence on antibody responses persisted beyond the time that IAEV maternal antibody could be detected. The importance of IAEV maternal antibody on the strategy of vaccination against IAE is discussed.     

Vaccinating chickens against avian influenza with fowlpox recombinants expressing the H7 haemagglutinin

OBJECTIVE: To evaluate the vaccine efficacy of a fowlpox virus recombinant expressing the H7 haemagglutinin of avian influenza virus in poultry. PROCEDURE: Specific-pathogen-free poultry were vaccinated with fowlpox recombinants expressing H7 or H1 haemagglutinins of influenza virus. Chickens were vaccinated at 2 or 7 days of age and challenged with virulent Australian avian influenza virus at 10 and 21 days later, respectively. Morbidity and mortality, body weight change and the development of immune responses to influenza haemagglutinin and nucleoprotein were recorded. RESULTS: Vaccination of poultry with fowlpox H7 avian influenza virus recombinants induced protective immune responses. All chickens vaccinated at 7 days of age and challenged 21 days later were protected from death. Few clinical signs of infection developed. In contrast, unvaccinated or chickens vaccinated with a non-recombinant fowlpox or a fowlpox expressing the H1 haemagglutinin of human influenza were highly susceptible to avian influenza. All those chickens died within 72 h of challenge. In younger chickens, vaccinated at 2 days of age and challenged 10 days later the protection was lower with 80% of chickens protected from death. Chickens surviving vaccination and challenge had high antibody responses to haemagglutinin and primary antibody responses to nucleoprotein suggesting that although vaccination protected substantially against disease it failed to completely prevent replication of the challenge avian influenza virus. CONCLUSION: Vaccination of chickens with fowlpox virus expressing the avian influenza H7 haemagglutinin provided good protection against experimental challenge with virulent avian influenza of H7 type. Although eradication will remain the method of first choice for control of avian influenza, in the circumstances of a continuing and widespread outbreak the availability of vaccines based upon fowlpox recombinants provides an additional method for disease control.     

Evaluation of the infectivity, length of infection, and immune response of a low-pathogenicity H7N2 avian influenza virus in specific-pathogen-free chickens

The H7N2 subtype of avian influenza virus (AIV) field isolate (H7N2/chicken/PA/3779-2/97), which caused the 1997-98 AIV outbreak in Pennsylvania, was evaluated for its infectivity, length of infection, and immune response in specific-pathogen-free (SPF) chickens. The composite findings of three clinical trials with various concentrations of virus indicated that this H7N2 subtype contained minimal pathogenicity for chickens. The concentration of the virus in the inoculum proved critical in the establishment of a productive infection in a chicken. Seven-day-old SPF chickens were not infected when inoculated with 10(0.7-2.0) mean embryo lethal dose (ELD50) of the H7N2 virus per bird. At this dose level, the immune response to this virus was not detected by the hemagglutination-inhibition (HI) test. Nonetheless, chickens at ages of 5 and 23 wk old tested were successfully infected when exposed to 10(4.7-5.7) ELD50 of H7N2 infectious doses per bird by various routes of administration and also by direct contact. Infected birds started shedding virus as early as 2 days postinoculation, and the period of virus shedding occurred mostly within 1 or 2 wk postinoculation (WPI). This H7N2 subtype of AIV induced a measurable immune response in all birds within 2 wk after virus exposure. Antibody titers were associated with AIV infectious doses and age of exposure of birds. Challenge of these infected birds with the same H7N2 virus at 5 and 10 WPI indicated the infective virus was recoverable from cloacal swabs at 3 days postchallenge and disappeared thereafter. In these challenged birds, the antibody levels as measured by the HI test spiked within 1-2 wk.     

Experimental infection of specific-pathogen-free chickens with avian rotaviruses

One-to-70-day-old specific-pathogen-free chickens were infected with rotaviruses isolated from chickens, turkeys, and pheasants. Chicks infected at 1 or 7 days of age remained largely free of infection: virus could be isolated from a few chicks of these ages, but virus antigen could not be detected in the epithelial cells of the intestinal villi. Treating the virus with trypsin before inoculation did not markedly enhance virus infectivity. The same batches of virus successfully infected chickens at 56 and 70 days of age: virus could be isolated between 1 and 5 days postinfection, and virus antigen was detected in the epithelial cells of the intestinal villi. Rotaviruses isolated from pheasants were infectious for 49-day-old chickens. All infections in the older chickens remained subclinical.     

The effects of age, route of exposure, and coinfection with infectious bursal disease virus on the pathogenicity and transmissibility of chicken anemia agent (CAA)

Specific-pathogen-free (SPF) chickens were inoculated with several different concentrations of chicken anemia agent (CAA) by the intra-abdominal, intratracheal, or oral routes. Based on lowered hematocrit values, the birds were most susceptible to CAA introduced by the intra-abdominal route. When SPF chickens were infected with infectious bursal disease virus (IBDV) at 1 day of age, they remained susceptible to CAA up to at least 21 days, whereas birds inoculated with CAA alone were susceptible only at 1 day of age. Infectious bursal disease virus introduced at 1 day of age also increased the susceptibility of birds to contact infection with CAA and resulted in increased mortality rates in CAA inoculates. The response of SPF birds to CAA infection varied following exposure at 1 day of age to two different strains of IBDV (STC and Variant-E). Chicken anemia agent contacts and inoculates infected with the Variant-E strain were affected 1 week earlier by CAA than by STC inoculates, as evidenced by depressed hematocrits. However, the total number of birds affected was similar for both the Variant-E and STC-inoculated chickens. Commercial broiler chickens inoculated at 1, 7, 10, and 14 days of age by non-parenteral routes with CAA or a combination of CAA and IBDV had mean hematocrits that were lower than controls. Several CAA-inoculated birds were considered anemic, with hematocrit values of 25 or less, while uninoculated birds remained within normal ranges.     

一例肾型鸡传染性支气管炎的诊断

2007年9月,郑州某鸡场发生一起疑似肾型鸡传染性支气管炎。将分离毒株接种20日龄肉鸡,于接种后第4 d出现精神不振、拉稀,第6 d出现死亡。分离病毒可致死部分鸡胚及产生卷曲胚,但不能凝集鸡红细胞,经1 %胰酶处理后能凝集鸡红细胞。经过实验室检查结果结合流行病学调查、临床症状和剖检变化,初步诊断为肾型鸡传染性支气管炎。     

Sequential mitogen stimulation of peripheral blood lymphocytes from chickens inoculated with infectious bursal disease virus

Chickens were inoculated wih the pathogenic Edgar strain of infectious bursal disease virus at 1 week, 2 weeks, or 1 day of age. In the 3 experiments, phytohemagglutinin stimulation of peripheral blood lymphocytes was significantly decreased on day 3 or 4 after inoculation. Subsequently, on days 7 through 21, stimulations were similar between lymphocytes from inoculated birds and those from control birds. Pokeweed mitogen stimulation was affected minimally in virus-inoculated chickens. In each experiment, on day 7, the spontaneous [3H]thymidine uptake was greater in nonstimulated lymphocyte cultures from inoculated chickens than in such cultures from control chickens. In an additional experiment, chickens 1 week of age were exposed to a pathogenic vaccinal virus given in their water. The vaccinal virus exposure resulted in significant decrease of phytohemagglutinin stimulation of lymphocytes on days 3 and 7 of the experiment. A significant decrease in pokeweed mitogen stimulation was observed on day 10 after inoculation.     

Experimental Escherichia coli respiratory infection in broilers

This study determined optimal conditions for experimental reproduction of colibacillosis by aerosol administration of avian pathogenic Escherichia coli to 2-to-4-wk-old broiler chickens. The basic model for reproducing disease was intranasal administration of approximately 10(4) mean embryo infectious dose of infectious bronchitis virus (IBV) followed by aerosol administration of an 02 or an 078 strain of E. coli in a Horsfall unit (100 ml of a suspension of 10(9) colony-forming units/ml over 40 min). Scores were assigned to groups of infected chickens on the basis of deaths; frequency and severity of lesions in the air sacs, liver and heart; and recovery of the challenge E. coli 6 days post-E. coli infection. An interval of 4 days between the IBV and E. coli challenges was best whether the chickens received the IBV at 8 or 20 days of age. Typically, 50%-80% of the chickens developed airsacculitis and 0 to 29% of the chickens developed pericarditis or perihepatitis, with little or no mortality. Escherichia coli alone resulted in no deaths and 0 to 20% airsacculitis, but these percentages increased to 0 to 5% and 52%-60% when the E. coli aerosol was administered through a cone-shaped chamber. Administration of IBV alone failed to induce lesions. Recovery of the challenge E. coli from chickens did not correlate well with lesions. On the basis of these data, administration of IBV to 20-day-old chickens followed 4 days later by exposure to an avian pathogenic E. coli reproduces avian colibacillosis with the low mortality, high percentage of airsacculitis, and low percentage of septicemic lesions characteristic of the conditions seen in the natural disease.     

一株肾型鸡传染性支气管炎病毒的初步分离鉴定

从哈尔滨市某肉鸡养殖场疑似传染性支气管炎的病死鸡中分离到1株肾型IBV,并对其进行鸡胚矮小化、血凝性、电镜下特征、新城疫干扰试验、致病性等生物学鉴定和N基因的RT-PCR鉴定。结果表明,该病毒分离株在鸡胚上传至第四代(F)4开始出现死亡或侏儒胚;病毒不凝集鸡红细胞;透射电镜下可见多呈球形、直径约80～120nm的病毒粒子,具有冠状病毒的典型形态特点;该病毒可干扰新城疫LaSota株在鸡胚中的增殖;将分离毒第4代尿囊液接种于6日龄雏鸡,7d后开始出现死亡,死亡率高达67%(6/9),病死鸡剖解后可见肾脏明显肿大、苍白,具有传染性支气管炎的典型病变;分离毒第5代尿囊液经N基因特异性RT-PCR获得大小约438bp的目的片断。初步确定所分离病毒为肾型IBV。     

Comparison of two infectious bursal disease vaccine strains: efficacy and potential hazards in susceptible and maternally immune birds.

Two infectious bursal disease vaccines were administered to separate groups of maternally immune and susceptible chickens at various ages. Vaccine B caused no damage to the bursae of chickens examined histologically at nine and 20 days after vaccination. The bursae of chickens given vaccine A were shown to be severely damaged when similarly examined. Both vaccines protected all the susceptible groups against challenge, but only vaccine A protected the groups of maternally immune chickens. Susceptible chickens vaccinated at one day of age with vaccine A showed a lowered response to Hitchner B1 Newcastle disease vaccine given at 14 days of age, judged by the haemagglutination-inhibition response and Newcastle disease challenge. The performance of the Newcastle disease vaccine was not affected in chickens given vaccine B. Bedding used by birds given vaccine A was shown to be capable of transmitting vaccinal virus to susceptible chickens, causing severe bursal damage.     

单抗免疫过氧化物酶技术检测鸡传染性支气管炎病毒

以抗鸡传染性支气管病毒（ＩＢＶ）核衣壳蛋白（Ｎ）的单抗株６ＤＨ８作为一抗,以辣根过氧化物酶标记的羊抗鼠ＩｇＧ作为二抗,建立了检测石蜡切片中ＩＢＶ抗原的单抗免疫过氧化物酶技术（Ｍｃ－ＩＰ）,并对人工攻毒鸡及临床ＩＢＶ感染疑似鸡进行了检测。在ＩＢＶＭ４１株人工攻毒鸡,用该技术于１～１２ｄ从气管、２～７ｄ从肾脏可以检测到ＩＢＶ抗原,阳性染色集中于气管粘膜上皮细胞及肾小管上皮细胞胞浆;临床疑为ＩＢＶ感染的病鸡,以Ｍｃ－ＩＰ技术和单抗免疫荧光试验（Ｍｃ－ＩＦＡ）同时进行检测,结果阳性率分别为９０．３％及８３．９％。     

The resistance to reinfection of tracheal organ cultures from chickens previously infected with avian infections bronchitis virus.

Lower titres of avian infectious bronchitis (AIB) virus were found following the infection of tracheal organ cultures prepared from chickens that had been given AIB virus intranasally six weeks previously than were found following the infection of organ cultures prepared from untreated or from passively-immune chickens. No infectious virus was found in the tracheal organ cultures at the time they were prepared.     

Gallid-1 herpesvirus infection in the chicken. 3. Reinvestigation of the pathogenesis of infectious laryngotracheitis in acute and early post-acute respiratory disease

Specific-pathogen-free chickens were infected via the trachea when 4 weeks old with 2000 plaque-forming units (PFU) of the virulent Australian infectious laryngotracheitis (ILT) virus strain CSW-1. Titers of ILT virus in the trachea were greatest (10(7.0) PFU/ml in washings, 10(6.0) PFU/g of tissue) 2-4 days postinfection (PI). Infectivity then declined rapidly, to become undetectable by 7 days PI, although highly localized areas of ILT antigen in the tracheal epithelium were occasionally observed by fluorescent antibody staining at 7 and 8 days PI. Tracheal organ cultures established 7 and 8 days PI provided no evidence of latent ILT virus infection at this immediate post-acute stage of pathogenesis. ILT virus was not isolated from peripheral blood leukocytes or lymphoid organs (spleen, bursa, thymus). ILT virus was found in the trigeminal ganglia and/or brain in 14 of 36 chickens (40%) examined between 4 and 7 days after intratracheal inoculation, but it was not in these tissues in five chickens examined at 8 days PI. Virus was also detected at 6 days PI in the trigeminal ganglia in one of five chickens infected by the conjunctival route. These data indicate that the early pathogenesis of ILT (CSW-1) infection frequently involves the tissues of the nervous system. In acute ILT in 4-week-old chickens, interferon-alpha/beta activity was not detectable in serum or tracheal exudates within 14 days PI, but tracheal washings contained significant virus-neutralizing activity by 7 and 8 days PI. In 3-day-old chickens infected via the trachea with 200 PFU of ILT CSW-1, the clearance of ILT virus from the trachea was similar to that observed in 4-week-old chickens, but ILT virus spread systemically to the livers of 20% by 5-7 days PI.     

鸡传染性贫血病毒与马立克氏病病毒共感染SPF鸡群免疫抑制协同作用的研究

将鸡传染性贫血病毒（Chicken infectious anemia virus,CIAV or CAV）和马立克氏病病毒（Marek s dis-ease virus,MDV）人工单一和共同感染1日龄的SPF鸡,感染后分别于14、21、28、35日龄检测鸡体红细胞压积的变化,并检测鸡群疫苗免疫3周后的抗体反应,以探讨CAV与MDV共感染对鸡体的免疫抑制是否有协同作用。结果表明,在血液分析方面,CAV与MDV共感染组较病毒单一感染组与对照组差异极显著,共感染不仅加重了鸡群贫血现象,而且延长了贫血的病理症状;而在禽流感病毒（Avian influenza virus,AIV）H5/H9疫苗、新城疫病毒（Newcastle disease virus,NDV）疫苗和传染性法氏囊病毒（Infectious bursal disease virus,IBDV）疫苗免疫后3周的抗体检测中,CAV与MDV共感染组较其它各实验组差异极显著,抗体滴度大大低于其它实验组;此外,CAV与MDV共感染组,鸡体生长状况明显差于实验各组,有6只鸡只死亡（6/25）,比病毒单一感染时的死亡率大大增加。综上研究证明,CAV与MDV共感染在免疫抑制作用上有协同作用。     

一株鸡传染性贫血病毒对不同日龄SPF鸡的致病性研究

为评价鸡传染性贫血病毒AV1550株的致病性,取1日龄、7日龄和14日龄SPF鸡分别经胸部肌肉注射不同病毒含量的病毒液,同时设置正常对照,隔离饲养观察21日。感染后14日采血测定红细胞压积,21日统计死亡率、体重变化以及胸腺、骨髓、法氏囊病变情况并测定1日龄SPF鸡感染后不同组织中的病毒载量。结果表明,1日龄SPF鸡感染AV1550株后,表现出精神沉郁、增重减缓、贫血等明显的临床症状,死亡率为53.9%;死亡鸡或观察期结束时存活鸡剖检,可见胸腺萎缩,骨髓变成淡黄色;不同剂量感染后14日,均能引起红细胞压积显著下降;21日时,胸腺病毒载量最高,可达106.7copies/mg 。7日龄SPF鸡感染后,出现增重减缓,高感染剂量（100000EID50）出现贫血,部分鸡出现胸腺萎缩和骨髓病变,但病变率低于30%。14日龄SPF鸡感染后,不引起明显临床症状。研究证实,CAV对SPF鸡的致病性具有明显的日龄依赖性,红细胞压积降低、骨髓病变、胸腺萎缩以及胸腺病毒载量测定可作为评价CAV致病的指标。     

1株肾型鸡传染性支气管炎病毒的鉴定

鸡传染性支气管炎病毒(IBV)具有不同致病特性,将IBV XDC-2株接种9日龄SPF鸡胚培养,可引起鸡胚死亡和出现侏儒胚,病毒EID50达5×10-5.33/mL。将IBV XDC-2株接种18日龄SPF鸡,饲养观察14 d,病鸡临床症状表现为:精神沉郁,羽毛凌乱,双翅下垂,轻微腹泻,多数拉白色水样稀粪。病死鸡出现肾肿大、呈花斑状、大量尿酸盐沉积。鸡发病率为100%,死亡率为25%。死亡鸡肺脏、肾组织制作组织切片,发现病理变化明显,主要为:肾小管扩张,上皮细胞呈玻璃样变性,部分管腔内可见坏死脱落之上皮细胞,于肾间质可见大量单核细胞浸润,肾间质有充血、出血现象;肺内动脉、毛细血管充血,淋巴细胞浸润。死亡鸡肺脏、肾组织接种鸡胚分离病毒,RT-PCR检测结果为阳性,表明该分离株为鸡传染性支气管炎病毒,具有很强的嗜肾性。