Bluetongue disease in Swiss sheep breeds: clinical signs after experimental infection with bluetongue virus serotype 8

Clinical disease of bluetongue (BT) in sheep may differ depending on breed, age and immunity of infected sheep and may also vary between serotype and strain of BT virus (BTV). Since there are no data available on the susceptibility of Swiss sheep breeds for BT, we performed experimental infection of the 4 most common Swiss sheep breeds and the highly susceptible Poll Dorset sheep with the BTV serotype 8 (BTV-8) circulating in Northern Europe since 2006. Clinical signs were assessed regarding severity, localisation, progression and time point of their appearance. The results clearly show that the Swiss sheep breeds investigated were susceptible to BTV-8 infection. They developed moderate, BT-characteristic symptoms, which were similar to those observed in Poll Dorset sheep. Regardless of breed, the majority of infected animals showed fever, swelling of the head as well as erosions of the mouth and subcutaneous haemorrhages.     

Toggenburg Orbivirus, a new bluetongue virus: Initial detection, first observations in field and experimental infection of goats and sheep

A novel bluetongue virus termed “Toggenburg Orbivirus” (TOV) was detected in two Swiss goat flocks. This orbivirus was characterized by sequencing of 7 of its 10 viral genome segments. The sequencing data revealed that this virus is likely to represent a new serotype of bluetongue virus [Hofmann, M.A., Renzullo, S., Mader, M., Chaignat, V., Worwa, G., Thuer, B., 2008b. Genetic characterization of Toggenburg Orbivirus (TOV) as a tentative 25th serotype of bluetongue virus, detected in goats from Switzerland. Emerg. Infect. Dis. 14, 1855–1861].In the field, no clinical signs were observed in TOV-infected adult goats; however, several stillborn and weak born kids were reported. Although born during a period of extremely low vector activity, one of these kids was found to be antibody and viral genome positive and died 3.5 weeks postpartum.Experimental infection of goats and sheep, using TOV-positive field blood samples, was performed to assess the pathogenicity of this virus.Goats did not show any clinical or pathological signs, whereas in sheep mild bluetongue-like clinical signs were observed. Necropsy of sheep demonstrated bluetongue-typical hemorrhages in the wall of the pulmonary artery. Viral RNA was detected in organs, e.g. spleen, palatine tonsils, lung and several lymph nodes of three experimentally infected animals.Unlike other bluetongue virus serotypes, it was not possible to propagate the virus, either from naturally or experimentally infected animals in any of the tested mammalian or insect cell lines or in embryonated chicken eggs.In small ruminants, TOV leads to mild bluetongue-like symptoms. Further investigations about prevalence of this virus are needed to increase the knowledge on its epidemiology.     

Bluetongue virus serotype 26: infection kinetics and pathogenesis in Dorset Poll sheep

Bluetongue virus serotype 26 (BTV-26) has recently been isolated from sheep in Kuwait. The aim of this study was to assess the pathogenicity and infection kinetics of BTV-26 in Dorset Poll sheep. Six sheep were experimentally infected with BTV-26 and samples taken throughout the study were used to determine the kinetics of infection using a pan specific BTV real time RT-PCR assay and two group specific ELISAs. Five of the six sheep showed mild clinical signs characteristic of bluetongue including conjunctivitis, reddening of the mouth mucosal membranes, slight oedema of the face and nasal discharge. Viral RNA was detected in 5 of the 6 sheep by real time RT-PCR, however the levels of viral RNA detected in the samples were lower and of shorter duration than seen with other field strains of BTV. Virus was isolated from the blood of infected animals at the peak of viraemia at around 9 dpi. Antibodies against BTV were first detected by 7 dpi using the early detection BTV ELISA and a little later (7-14 dpi) using a BTV specific competitive ELISA. Four of the five remaining sheep developed neutralising antibodies to BTV-26, measured by a serum neutralisation test (SNT), with titres (log(10)) ranging from 1.40 to 2.08.     

Bluetongue virus in the French Island of Reunion

This paper records the results of a bluetongue virus (BTV) serological survey and reports the first isolation of BTV on the French Island of Reunion. In January 2003, the French Island of Reunion, located off the coast of Madagascar, reported an outbreak of disease in cattle that resembled clinical bluetongue (BT) in sheep. The suspected causal agent was isolated and identified as epizootic haemorrhagic disease of deer virus (EHDV). However, because of the similarity in the clinical signs to those of BT, a retrospective survey against BTV was carried out using sera collected in 2002. Results revealed the presence of antibody in all sera tested indicating that BTV has been resident on the Island since 2002, and probably earlier. Although up to July 2003 no clinical BT had ever been reported in sheep, BTV viral RNA was amplified by RT-PCR from a single sheep blood collected in February that year, which strongly suggested that BTV was currently circulating on the Island. Following a second outbreak of disease in August 2003, this time involving a flock of Merino sheep, infectious BTV was finally isolated, and identified by both traditional and molecular techniques as serotype 3. The nucleotide and amino-acid sequences of the RT-PCR products amplified for BTV segments 7 and 10 from the sheep blood collected in February and August from different areas of the Island, were sufficiently diverse as to suggest that they were of different origins and/or different BTV serotypes.     

CLINICO-PATHOLOGICAL EFFECT OF BLUETONGUE VIRUS SEROTYPE 20 IN SHEEP

Fifty-four Merino crossbred sheep were inoculated with bluetongue virus serotype 20 (BTV-20) by the intravenous, subcutaneous and intradermal routes. BTV-20 was successfully transmitted by Culicoides (Avaritia) spp. No. 5 to two additional sheep. Clinical and pathological effects were studied. In the artificially infected sheep, clinical signs were observed after an incubation period of 6 to 10 days and consisted of pyrexia, oral and subcutaneous hyperaemia mild oedema of the ears, face and lips, and coronitis. The major internal pathological changes were petechial and ecchymotic haemorrhages in the tunica media of the pulmonary artery near its junction with the heart and mild haemorrhage and mild oedema in the intestines, coronet, lips, cheeks and ears. Viraemia was detected between day 2 and day 14 post inoculation. The two sheep infected by insect transmission were mildly affected and became viraemic between 16 and 19 days after transmission. No deaths occurred and under experimental conditions BTV-20 caused only mild disease in housed sheep. To date there has been no reported outbreak of natural bluetongue infection in Australia. Compared to other serotypes BTV-20 appears to be of low pathogenicity in sheep.     

Bluetongue virus serotypes 20 and 17 infections in sheep: Comparison of clinical and serological responses

The clinical, virological and serological responses of sheep infected with an Australian bluetongue virus (BTV) isolate (serotype 20) were compared to responses in sheep inoculated with an American bluetongue isolate (serotype 17) with which it had shown cross-reactions in serum neutralization tests. In sheep inoculated with BTV 20, clinical signs were very mild and viremia was first detected by day 5; virus was isolated intermittently for a further 2 to 3 days. Neutralizing and precipitating antibodies were first detected in the serum of the sheep between 2 to 3 weeks following inoculation. In contrast, sheep inoculated with BTV 17 showed pyrexia and severe hyperemia of the nasolabial area and oral mucosa from day 7 to 17. Viremia was first detected on day 3 and extended to day 20, while the appearance and titers of serum antibodies was similar in both groups.After challenge with BTV 17 the sheep in both groups remained clinically normal, and virus was not detected in the blood; however, serum neutralizing antibody titers to both viruses increased 2 weeks after challenge and the mean titer of the two groups ranged from 1:250 to 1:640.     

The impact of bluetongue virus on reproduction

Bluetongue virus has been recognized as an important noncontagious, arthropodborne infectious viral disease of ruminants. 24 different serotypes of virus have been recognized world-wide. The most severe clinical disease has been associated with severe clinical disease in sheep and some free ranging wild ruminants. A number of reports have implicated the viruses as causing reproductive disorders in both males and females. The bluetongue related reproductive disorders include early embryonic deaths, abortions, malformed fetal calves or lambs, transient infertility in bulls and rams, and shedding of virus in semen. Recently, bluetongue virus contamination of modified live commercial canine vaccine was associated with abortion and acute death of pregnant bitches. The pathogenesis of these various aspects of reproductive failure are discussed herein.     

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.     

Survey of desert bighorn sheep in California for exposure to selected infectious diseases

From February 1983 to June 1985, 188 desert bighorn sheep (Ovis canadensis nelsoni, = 161 and Oc cremnobates, = 27) from 18 herds in 17 mountain ranges and one captive herd were caught, marked, and had blood, fecal, and nasal mucus samples collected. Nasal swab specimens were cultured bacteriologically and virologically specifically for parainfluenza-3 (PI-3) virus. Bacterial flora differed from herd to herd. Pathogenic pneumophilic bacteria (eg, Pasteurella sp) seldom were found. Parainfluenza-3 virus was isolated from 6 bighorn sheep in 3 herds. Fecal specimens were examined for parasite ova and low numbers of lungworm (Protostrongylus sp) larvae were found in feces from 2 herds. Sera were evaluated for antibodies against respiratory syncytial virus, ovine progressive pneumonia, infectious bovine rhinotracheitis, PI-3, bovine viral diarrhea, brucellosis, leptospirosis, contagious ecthyma, bluetongue, and epizootic hemorrhagic disease. Blood clots were cultured virologically for bluetongue and epizootic hemorrhagic disease. Serologic evidence of bluetongue and/or epizootic hemorrhagic disease was found in 9 herds, and bluetongue virus (serotypes 10,11,13 and 17) was isolated from 3 herds. Antibody titers against PI-3 and respiratory syncytial virus were found in 9 and 13 herds, respectively. Evidence of bovine viral diarrhea infection was found in 6 herds, whereas infectious bovine rhinotracheitis was found in only 1 herd. Antibody titers against contagious ecthyma were found in 9 of 18 herds in California, and active lesions were seen occasionally. Evidence of ovine progressive pneumonia, leptospirosis, or brucellosis was not found.     

Identification of seven serotypes of bluetongue virus from the People's Republic of China

Seven serotypes (1, 2, 3, 4, 12, 15 and 16) of bluetongue virus were isolated from the blood of sheep and cattle in the People's Republic of China between 1986 and 1996. Six of these viruses were isolated in Yunnan province. The sheep from which serotypes 1 and 16 were isolated showed obvious signs of bluetongue disease, whereas the cattle from which serotypes 2, 3, 4, 12 and 15 were isolated were clinically normal. Phylogenetic analyses of these viruses indicate that they are more closely related to one another, and to an Australian strain of serotype 1, than they are to prototype strains of bluetongue virus serotypes 2, 10, 11, 13 and 17 from the USA.     

Recovery of dual serotypes of bluetongue virus from infected sheep and cattle

Dual serotypes of bluetongue virus (BTV) were recovered from field-collected samples of sheep and cattle blood. Two sheep, each infected with both BTV serotypes 10 and 17, were found in a flock with bluetongue disease associated with these two serotypes. One sheep infected with BTV serotypes 11 and 17 was found in a second flock; it was the only viremic sheep detected and was clinically ill. Dual serotype infections of one beef and two dairy cattle were found in three geographically separate herds; mixtures recovered were of BTV serotypes 10 and 17 and serotypes 11 and 17. Clinical signs of illness were absent in the cattle in two herds, but severe conjuctivitis was seen in several cows in a third herd, including the cow with a dual serotype infection (BTV 11 and 17). Two of the cattle with dual infections had no serological evidence of BTV as determined by the agar gel precipitin test; serum was not available from the other cow with a dual serotype infection. The significance of dual infections and immune tolerance are discussed.     

THE CONTROL OF BLUETONGUE IN AN ENZOOTIC SITUATION

On account of the wide host range of bluetongue virus and its biological transmission by insects, control of the disease in an enzootic situation is based primarily on the active immunisation of susceptible animals as well as on the prevention of contact between the insect vectors and the susceptible hosts. In spite of their unquestionable value, the egg attenuated vaccines which are currently employed for prophylactic immunisation, have certain shortcomings. The existence of 16 known serotypes of bluetongue virus makes it difficult to achieve a very wide spectrum of immunity in sheep vaccinated once or twice only. The problems which are experienced with the immunisation of lambs born in spring are indicated. The present vaccine can also present problems when used in breeding animals. Furthermore, the costs involved in the annual vaccination of large numbers of animals are considerable. The need for a vaccine for cattle is indicated. Work is also being conducted at present on the development of an inactivated vaccine for use in sheep. The use of novel virological techniques may aid in the future development of absolutely safe and highly efficient vaccines against bluetongue.     

青海省绵羊品种与引进品种先天性免疫研究

为研究青海本地绵羊品种与引进品种的先天性免疫水平和品种特性,本研究选取青海省不同海拔地区的2个本地品种（欧拉羊、白藏羊）和1个引进品种（无角道赛特羊）共186只绵羊,采集新鲜血样,进行血常规检测（白细胞数（WBC）、红细胞数（RBC）、平均红细胞血红蛋白（HGB）、红细胞压积（HCT）、平均红细胞体积（MCV）、平均红细胞血红蛋白浓度（MCH）、血红蛋白浓度（MCHC）、血小板（PLT）、红细胞分布宽度（RDW-CV）、淋巴细胞百分比（LYM%））;制备血清,用绵羊ELISA试剂盒测定白介素-1（IL-1）、白介素-2（IL-2）、白介素-6（IL-6）、白介素-18（IL-18）、γ-干扰素（IFN-γ）、免疫球蛋白G （IgG）和主要组织相容性复合体（MHC）等免疫指标;分别以品种和品种来源地为因变量对检测结果进行比较分析。结果发现,以品种为因变量,无角道赛特羊的免疫水平最高,白藏羊的抗病性稍高于欧拉羊;以品种来源地为因变量时,本地绵羊品种的先天性免疫水平低于引进绵羊品种,对疾病的抵抗力较弱,除MCH、MCHC和RDW-CV外,无角道赛特羊在血液生化水平上均高于青海本地品种,说明无角道赛特羊是具有高抗病能力的优良品种。本试验为不同绵羊品种机体先天性免疫水平的研究提供了参考数据,对青海藏羊的选育工作和品种改良具有指导意义。     

无角陶赛特羊和特克塞尔羊繁殖性能及生长性能的研究

该研究旨在初步了解无角陶赛特羊和特克塞尔羊对甘肃榆中地区的适应性,以便为该地区引进推广良种肉羊提供依据。以兰州奉特动物科技有限公司榆中肉羊繁育中心的无角陶赛特羊和特克塞尔羊为研究对象,对其2016—2018年的繁殖性能进行了分析,同时对2018年无角陶赛特羔羊和特克塞尔羔羊从出生到2月龄(断奶)的生长发育性能进行了测定。结果表明:从2016年到2018年无角陶赛特羊、特克塞尔羊的繁殖率、产羔率、双羔率均在逐年提高;特克塞尔羔羊初生重、1月龄重以及2月龄重均高于无角陶赛特羔羊,但差异均不显著(P>0.05);特克塞尔羔羊1月龄胸宽、2月龄胸宽和体长均显著高于无角陶赛特羔羊(P<0.05),其他体尺指标差异均不显著(P>0.05)。说明两个肉羊品种在甘肃榆中地区均有良好的繁殖性能以及较高的生长性能,均可在榆中及其周边地区推广养殖。     

Antibodies to bluetongue viruses in animals imported into United States zoological gardens.

Three hundred forty-five serum samples from 30 zoological animal species which had been imported into the United States were examined retrospectively for the presence of antibody to bluetongue viruses. Ninety eight (28.4%) were positive for antibody to bluetongue group antigen by the bluetongue agar gel immunodiffusion test. Bluetongue antibodies, most of which were against serotypes exotic to the United States, were detected in 13 animal species from Africa not previously reported to be infected by bluetongue virus. The lack of virus neutralizing antibody to any of the 20 known bluetongue virus types in four of the 28 positive serums studied may indicate the existence of new bluetongue virus serotypes, cross reactions with other orbiviruses or a more rapid decline of neutralizing than precipitating antibody. The possibility of recrudescence of bluetongue virus infection from some inapparently infected zoological animals and existence of a known bluetongue vector (Culicoides variipennis) in the United States would suggest that further assessment of bluetongue in zoological animals be made.     

Bluetongue and epizootic hemorrhagic disease virus isolation from vertebrate and invertebrate hosts at a common geographic site

One serotype of bluetongue virus (BTV) and two serotypes of epizootic hemorrhagic disease virus (EHDV) were isolated from vertebrate and invertebrate hosts on a farm in Colorado. The isolations were from blood samples collected a week apart from a dairy heifer with stomatitis and laminitis; EHDV serotypes 1 and 2 were isolated from the first blood sample, and BTV serotype 13 and EHDV serotype 1 were isolated from the second. Antibodies to EHDV and BTV were detected in the serum from this heifer. Both EHDV serotypes and BTV serotype 13 were isolated from pools of female biting gnats (Culicoides variipennis) that had not had a recent blood meal. The BTV insect isolate was biologically transmitted by female gnats from an infected donor sheep to a recipient host sheep. Culicoides variipennis was the predominant insect collected during three nights of light trap captures at the farm.     

Serological evidence of the occurrence of bluetongue in Iraq.

Precipitating antibodies against bluetongue were detected in sheep and goat serum samples collected from animals slaughtered in Baghdad abattoir. Out of 294 sheep serum samples and 110 goat serum samples examined, 28 and 18 samples respectively showed precipitating activity. In addition, examination of sheep serum samples collected from localities where clinical cases similar to bluetongue were previously reported revealed the presence of bluetongue precipitating antibodies in 101 sera out of 198 samples examined. This is the first report confirming the occurrence of bluetongue in Iraq.     

Bluetongue in exotic sheep in Cameroon

Bluetongue virus (BTV) was diagnosed in the Animal Research Institute, Mankon, Bamenda from tissue samples collected from five sheep of exotic breeds which had died of suspected bluetongue in a series of outbreaks between June and October 1982. Five serotypes BTV 1, 4, 5, 12 and 14 were isolated during the period mentioned. Similar disease occurred during June of the following year and BTV type 16 was isolated from a spleen sample from a dead sheep.     

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.