Serological reactions in sheep and cattle experimentally infected with three Australian isolates of bluetongue virus

Serums from 103 sheep and 24 cattle experimentally infected with one of 3 serotypes of bluetongue virus isolated in Australia were tested for antibody to bluetongue virus in the serum neutralisation test and the agar gel diffusion precipitin test. Antibody to bluetongue virus was first detected by these tests 8 to 10 days after intravenous infection in 4 sheep that were bled daily for serum analysis. The agar gel diffusion test failed to detect antibody in 28% (29/103) of sheep which had seroconverted in the serum neutralisation test. A further 7% (7/103) of sheep serums were negative in both tests 14 to 22 d after infection. Both tests detected antibody to bluetongue virus in all cattle serums by 10 days after detection of viraemia. In comparison with the intravenous route of infection, extended prepatent periods for the commencement of viraemia resulting from intradermal, subcutaneous and intrauterine routes of infection in the cattle caused corresponding delays in the detection of antibody. For example, one cow that was infected by intrauterine inoculation did not become viraemic until 22 d after inoculation and antibody was not detected until 32 d after inoculation.     

Clinical pathology of Australian bluetongue virus serotype 16 infection in Merino sheep

SUMMARY Viraemic blood from an ox naturally infected with Australian bluetongue (BLU) virus serotype 16 was passaged twice in sheep. Twelve 2- to 4-years-old Merino ewes, negative in a bluetongue agar gel Immunodiffusion test, were Inoculated with viraemic blood from the second sheep passage. They were examined for 18 days and compared with a control group. Significant changes in haematological measurements, namely packed cell volume, total white cell count and lymphocyte count, and in plasma enzyme concentrations, namely aspartate transaminase and creatine kinase, occurred in the infected sheep. All Infected sheep became sick. The antibody response, and clinical and necropsy findings were consistent with other reports of mild to moderate disease with Australian BLU serotypes.     

Virulence of bluetongue virus for British sheep

A South African isolate of bluetongue virus type 3 was inoculated intradermally into three different breeds of British sheep under conditions designed to test its virulence in animals under stress. All animals inoculated developed a pyrexia and viraemia followed by clinical evidence of bluetongue disease. Marked alterations in serum enzyme levels, in particular of creatine phosphokinase, lactate dehydrogenase and aldolase occurred in the more severely affected animals. Nine out of the 12 inoculated animals subsequently died. No major differences in response could be detected in the different breeds of sheep nor in the stressed compared with the unstressed groups. The virulence of this bluetongue virus isolate was thereby confirmed and its potential risk to the British sheep industry. Consequently, stringent import regulations must be maintained to prevent its entry into Britain.     

Nontransmission of bluetongue virus by embryos from bluetongue virus-infected sheep

Donor sheep were infected either by bites of bluetongue virus (BTV)-infected (serotype 11, "Texas Station strain") Culicoides variipennis or by inoculation with 100,000 median chicken embryo intravascular lethal doses of BTV (serotype 11) from a suspension made from infected C variipennis. Fourteen embryos from 4 BTV-infected ewes bred by rams not infected with BTV were transferred to 8 BTV-seronegative recipient ewes, and 35 embryos and 4 unfertilized eggs from 14 BTV-infected ewes bred by BTV-infected rams were transferred to 19 BTV-seronegative recipient ewes. Eleven pregnancies and 12 lambs resulted. None of the recipients or lambs seroconverted, and BTV was not isolated from the pregnant recipient ewes or their lambs at slaughter 30 days after parturition.     

3株新城疫病毒毒力的测定

新城疫是由新城疫病毒引起鸡的一种高度接触性传染病。为了探讨本地有关区域 NDV毒力分布情况 ,将自 1 997年以来 ,从珠江三角洲不同地区分离获得的 3株 NDV的鸡胚平均致死时间 ( MDT)、1日龄雏鸡脑内致病指数 ( ICPI)和 6周龄鸡静脉内致病指数 ( IVPI)进行测定。1　材料与方法1 .1　病毒　ND野毒株 ,共 3株 ,包括 N株 (分离自南边 )、S株 (分离自狮山 )、L株 (分离自罗定 )均由本实验室分离、鉴定保存。1 .2　实验动物　 1 0日龄鸡胚、1日龄易感雏鸡 ,6周龄非 ND免疫雏鸡均由佛山燎原鸡场提供。1 .3　毒株的鸡胚传代　将 3株 ND…     

Serial inoculation of sheep with two bluetongue virus types

Groups of sheep inoculated with bluetongue virus type 4 were challenged at various intervals after inoculation (from seven to 70 days) with bluetongue virus type 3. Examination of the clinical and serological response showed that animals were protected from challenge with a second bluetongue virus for up to 14 days after the inoculation of the first virus type. An adoptive transfer experiment in monozygotic sheep involving both antibody and T lymphocytes was carried out. Only partial protection was observed against heterologous virus challenge, indicating that although the T cell response has a cross-protective component, antibody is not involved. These observations indicate that current vaccination procedures should be reappraised, particularly in terms of revaccination with multiple bluetongue virus type.     

Dot immunobinding assay for the detection of bluetongue virus antibodies in sheep experimentally inoculated with bluetongue virus type 1.

Dot immunobinding assay (DIA) was evaluated for the detection of bluetongue virus (BTV) antibodies in sheep experimentally inoculated with BTV 1. Serum samples collected on 14, 21, 28, 43 and 60 day post infection (dpi) were positive for precipitating antibodies by the agar gel precipitation test (AGPT) while antibodies could be detected as early as 7 dpi by DIA and ELISA. Virus neutralizing antibodies were detected first at 14 dpi. The sensitivity of the four tests was compared on the same serum samples collected at different intervals. The results indicated that DIA was more sensitive than AGPT and the serum neutralization test and as sensitive as ELISA. Thus due to sensitivity simplicity and economy, DIA could replace AGPT for diagnosis and serological survey for BTV infection in animals.     

9株猪瘟分离毒株的致病特性

采用9株临床表现强、中、低致病特点的猪瘟野毒分离株第3代细胞毒作为种毒,按3mL/头剂量分别注射猪瘟抗原及抗体阴性猪,再用上一代传代猪发病后的血毒作为下一代接毒用种毒接种试验猪1头或2头,或上一代传代猪发病后,同圈放入1头或2头试验猪进行同居感染.如此进行,GDGZ1/95、BJCY1/96和JL1/94传至8代;FJFQ1/99传至7代;HeBHH1/95、HeNBY1/96、BJTX3/96、GXBH1/98和HeNXH2/98传至3代.结果显示:上述分离株传至3～5代过程中均表现出毒力增强的趋势,从3～5代传代到8(7)代的过程中毒力进一步增强并保持稳定,且均超过了标准石门强毒株的发病特点.所有试验猪均出现较典型的猪瘟临床症状,解剖后均表现出不同程度的病理变化,死后或解剖后的各种脏器经HCFA检查均为强阳性,这种现象进一步证实了猪是猪瘟病毒的敏感动物,各毒株之间毒力没有明显差异.对其中7株分离株传代血毒部分代次E2基因主要区域进行序列分析,结果仅GDGZ1/95株从F1～F8代中的F6代有2个核苷酸的差异,引起1个相应氨基酸的变异,其余毒株的不同代次没有碱基发生变异,初步说明猪瘟病毒基因型表现相对的稳定性.     

Observations on transplacental infection with bluetongue virus in sheep

Twenty-four ewes were inoculated with 1 of 2 strains of bluetongue virus type 4 at 40, 60, or 80 days of gestation. Two ewes aborted, 2 ewes died, and 1 was killed during the experiment, but their fetuses were recovered. At term, 2 mummified fetuses, 4 dead lambs, and 17 clinically healthy lambs were produced by 12 sheep, and the remaining 7 sheep were barren. Porencephaly and cerebellar dysgenesis were found in term lambs born to sheep inoculated at 40 and 60 days of gestation. Radiographic examination of 12 fetuses showed developmental ages far less than their chronologic age; 8 fetuses had skeletal growth-retardation lines, which were also observed in the dead lambs. A systemic lymphoreticular hyperplasia was observed in the dead lambs and in all lambs at 12 weeks of age; in 4 of the latter, granulomatous reactions were present in the liver and kidney. Lungs of the full-term lambs were reduced in weight and showed poor alveolar development and mononuclear cell infiltration, which persisted in the 12-week-old lambs. It was concluded that bluetongue virus is capable of causing not only gross abnormalities of the CNS, but also generalized growth retardation and fetal lymphoreticular hyperplasia.     

Prevalence of bluetongue virus antibodies in sheep in central Ethiopia

Competitive ELISA was applied to detect antibodies against bluetongue virus in sheep sera collected from different agro-climatic areas in Ethiopia. A total of 90 serum samples were tested and 42 (46.67%) were positive for bluetongue virus antibodies. A prevalence rate ranging from 9.67% for sheep sampled in the highland to 92.85% for sheep sampled in the lowland was recorded. The prevalence correlated with the probable distribution of the Culicoides vector. This is the first report indicating the presence of bluetongue virus infection in animals from Ethiopia.     

Evaluation of bluetongue virus diagnostic tests in free-ranging bighorn sheep

Five bluetongue virus (BTV) diagnostic tests were evaluated for use in free-ranging bighorn sheep. We sampled one bighorn sheep population four times between 1989 and 1995. The tests evaluated included virus isolation (VI), polymerase-chain reaction (PCR), serum neutralization (SN), agar-gel immunodiffusion (AGID), and competitive enzyme-linked immunosorbent assay (c-ELISA). The c-ELISA, AGID and SN tests had high levels of agreement in determining serogroup exposure in bighorn sheep. We used maximum-likelihood algorithms to estimate the parameters of each diagnostic test used. Although the c-ELISA and AGID had high sensitivity and specificity, the SN had perfect specificity but lower apparent sensitivity. Due to the potential of cross-reactions among multiple serotypes, results of the SN must be interpreted with caution when assessing serotype exposure in an area where multiple serotypes are endemic. The PCR assay delineated convalescent antibody titers from more-recent infections, and consequently, was pivotal in distinguishing a different exposure pattern between the bighorn sheep and cattle in an adjacent herd. Based on an increasing seroprevalence (50% to 100%), BTV circulated through this bighorn sheep population between 1989 and 1993. This increase in seroprevalence coincided with a bighorn die-off due to BTV infection in June, 1991. An adjacent cattle herd was sampled in 1995 for comparison. The bighorn sheep and adjacent cattle had different patterns of exposure to BTV between 1994 and 1995. There was no evidence that BTV circulated through the bighorn sheep population from 1994 to 1995. In 1995, seroprevalence to BTV decreased to 72%, none of yearling bighorn was seropositive, and all of the 39 bighorn sheep were PCR-negative. In contrast, all adult cattle were seropositive to BTV by c-ELISA and SN, and 4 of the calves were seropositive; 11 of the 24 cattle were PCR-positive, including all five calves. Overall, the pattern of temporal herd immunity in the bighorn sheep appeared to follow a classic epidemic curve, with the appearance and subsequent disappearance of herd immunity coinciding with the 1991 die-off in this population. As low levels of herd immunity and high proportions of susceptible animals are key factors in the development of epidemics, this population of bighorn sheep may be at increased risk for a BTV epidemic in the future.     

Immunologic response of sheep to inactivated and virulent bluetongue virus

Humoral and cellular immune responses of sheep to inactivated and virulent bluetongue virus (BTV) were studied. All sheep inoculated with inactivated BTV developed BTV group-specific nonneutralizing antibodies, as determined by agar-gel immunodiffusion. The development of group-specific, nonneutralizing, complement-fixing antibodies was variable and appeared to be dependent on immunizing BTV serotype, sheep breed, and individual variation. Virus-neutralizing antibodies were never detected after inoculation with the inactivated BTV. In vitro lymphocyte stimulation to BTV soluble antigen was observed with cells from all inoculated Warhill sheep and with cells from 1 of 3 inoculated Suffolk cross sheep. Complement-fixation titers did not appear to correlate with the degree of protection observed, ie, duration of postchallenge-exposure viremia. The development of postchallenge-exposure neutralizing antibody titer was inversely correlated to protective immunity. The development of a response to BTV antigen in the lymphocyte-stimulation test associated most closely with protection. Warhill sheep were afforded better protection, by inoculation with inactivated BTV, to live virus challenge exposure than were the Suffolk cross sheep. Approximately 30% of the inoculated Suffolk cross sheep responded to challenge exposure with intensified clinical signs of blue-tongue, compared with the challenge-exposed control sheep of the same breed.     

4个传染性囊病野毒株的致病性试验

传染性囊病(infectious brusal disease,IBD)是由传染性囊病病毒(infectious brusal disease virus,IBDV)引起的一种急性、高度接触性、高度传染性的病毒病.自20世纪60年代发现传染性囊病(IBD)以来,给世界养禽业带来了极大的损失.对养禽业影响更严重的是,欧洲国家及我国相继出现了vvIBDV方面的报道,其致死率达到了100%[1-4].     

Pathogenicity of infectious bronchitis virus isolates from Ontario chickens

Infectious bronchitis (IB) is one of the important viral diseases of chickens, and in spite of regular vaccination, IB is a continuous problem in Canadian poultry operations. In an earlier study using sentinel chickens we determined the incidence of infectious bronchitis virus (IBV) in Ontario commercial layer flocks. The objective of this study was to determine the pathogenicity of 5 nonvaccine-related IBV isolates recovered from the sentinel birds. The clinical signs, gross, and histological lesions in specific pathogen-free chickens indicated that all 5 isolates caused mild lesions in the respiratory tract. An important finding of this study was the significantly lower average daily weight gain among virus-inoculated groups of chickens during the acute phase of infection. Based on sequences of part of the S1 gene IBV-ON2, IBV-ON3, and IBV-ON5 formed a cluster and they were closely related to strain CU-82792. IBV-ON4 had 98.7% identity with the strain PA/1220/9, a nephropathogenic variant.